Chronicling the Golden Age of Astronomy

The invention of the telescope at the dawning of the 17th century has revolutionized humanity's understanding of the Universe and our place within it. This book traces the development of the telescope over four centuries, as well as the many personalities who used it to uncover brand-new revelations about the Sun, Moon, planets, stars and distant galaxies.Starting with early observers such as Thomas Harriot, Galileo, Johannes Hevelius, Giovanni Domenico Cassini, Robert Hooke and Christian Huygens, the book explores how these early observers arrived at essentially correct ideas concerning the objects they studied. Moving into the 18th and 19th centuries, the author describes the increasing sophistication of telescopes both large and small, and the celebrated figures who used them so productively, including the Herschels, Charles Messier, William Lassell and the Earls of Rosse. Many great discoveries were also made with smaller instruments when placed in the capable hands of the Struve dynasty, F.W. Bessel, Angelo Secchi and S.W Burnham, to name but a few. Nor were all great observers of professional ilk. The book explores the contributions made by the 'clerical astronomers,' William Rutter Dawes, Thomas William Webb, T.E.R Philips and T.H.E.C Espin, as well as the lonely vigils of E.E. Barnard, William F. Denning and Charles Grover. And in the 20th century, the work of Percival Lowell, Leslie Peltier, Eugene M. Antoniadi, Clyde Tombaugh, Walter Scott Houston, David H. Levy and Sir Patrick Moore is fully explored. Generously illustrated throughout, this treasure trove of astronomical history shows how each observer's work led to seminal developments in science, and providing key insights into how we go about exploring the heavens today.


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Historical & Cultural Astronomy Series Editor: Wayne Orchiston

Neil English

Chronicling the Golden Age of Astronomy A History of Visual Observing from Harriot to Moore

Historical & Cultural Astronomy

Series Editor: WAYNE ORCHISTON, Adjunct Professor, Astrophysics Group, University of Southern Queensland, Toowoomba, Queensland, Australia ([email protected]) Editorial Board: JAMES EVANS, University of Puget Sound, USA MILLER GOSS, National Radio Astronomy Observatory, USA DUANE HAMACHER, Monash University, Melbourne, Australia JAMES LEQUEUX, Observatoire de Paris, France SIMON MITTON, St. Edmund’s College Cambridge University, UK MARC ROTHENBERG, AAS Historical Astronomy Division Chair, USA VIRGINIA TRIMBLE, University of California Irvine, USA XIAOCHUN SUN, Institute of History of Natural Science, China GUDRUN WOLFSCHMIDT, Institute for History of Science and Technology, Germany

More information about this series at http://www.springer.com/series/15156

Neil English

Chronicling the Golden Age of Astronomy A History of Visual Observing from Harriot to Moore

Neil English Fintry by Glasgow, UK

ISSN 2509-310X     ISSN 2509-3118 (electronic) Historical & Cultural Astronomy ISBN 978-3-319-97706-5    ISBN 978-3-319-97707-2 (eBook) https://doi.org/10.1007/978-3-319-97707-2 Library of Congress Control Number: 2018954056 © Springer Nature Switzerland AG 2018 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Fig. 1  Tiberius, the author’s 5-in. f/12 classical achromatic refractor. (Image by the author)

Do the words of a poem lose their poignancy once its author departs this world? Can the limp of ‘progress’ outshine the ‘grand procession’ of great accomplishment? Can a culture, basking in the glory of its own achievement, be made mute by a faithless generation of technocrats? Can an optical bench test inspire more than a night spent behind the eyepiece of a grand old telescope? v

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vi Let us venerate that which is deserving of veneration! Whose crown shall we adorn with a laurel wreath? Let us sing again of old dead men And clear the cobwebs from their medals. For they have no equal in the present age No muse to light their way. —Neil English

It has been said that those who are ignorant of history are likely to make the same mistakes over and over again. But it is equally true that the same person is likely to underestimate the achievements of our forebears. This is particularly true of the history of astronomy, where dedicated men and women turned their telescopes skyward in an attempt to make sense of the universe in which they found themselves. The telescope has enjoyed four centuries of development, radiating into a veritable smorgasbord of form and function. For nearly two centuries, the slender tube of the refracting telescope dominated the astronomical world. And yet slowly but surely, adventurous individuals developed entirely novel means of observing the starry heaven using mirrors instead of lenses, and in the twentieth century, clever opticians combined the best properties of both, by bringing to market compound telescopes represented by the Schmidt-Cassegrain, Maksutov-Cassegrain, and other catadioptric forms enjoyed by amateurs today.

Fig. 2  Denis Buczynski, with his dear old Brashear achromatic refractor. (Image by the author)

On our journey through the maze that is the history of amateur and professional astronomy, we shall discover much about the personalities behind the most momentous discoveries made visually at the telescope, what motivated and inspired their

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prolonged study of the starry heaven, often with very modest equipment. On our journey through four centuries of time, we shall explore the discoveries made by countless individuals, many of which have long been forgotten by our c­ ontemporaries. If you have been guided only by discussions on modern forums on the Internet, chances are good that you will be kept completely in the dark about tips and techniques used by lesser known individuals that aided their study of the celestial realm. Who discovered the effects of colored filters? When was resolving power linked to the wavelength of light? Why did the long focus achromatic refractor do so well in the study of double and multiple star systems? Studying the details of past lives dedicated to astronomy can also help dispel some myths perpetuated by some contemporary amateurs. Can modern apochromatic refractors resolve double stars better than the classical refractor? Historical investigation provides the answer  – no. Are refractors better than reflecting telescopes in resolving double stars? Again the answer is: not necessarily. How impor-

Fig. 3  Drawings of Jupiter made in 1908 and 1909 by the Reverend T.E.R Philips using a 12.5-in. Calver reflector. (Image courtesy of the BAA)

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tant is the character of the individual and his or her level of training in seeing telescopically? As we shall discover, the answer is: very important! Many an individual is on record for stating that they hardly ever encounter clear skies. How true is this statement? As we shall discover, the study of history can shed much light on this question. In short, those that ignore the historical literature are prone to drawing erroneous conclusions of what can and cannot be achieved with a given telescope today. A detailed look at what our astronomical forebears believed also has a bearing on what they allegedly saw through their telescopes. The most obvious example is the case of Percival Lowell, who sincerely believed that intelligent beings existed on our planetary neighbor, Mars. The “canals” he drew at the eyepiece of the 24-in. refractor he erected at Flagstaff, Arizona, reflected his mistaken worldview that life was an inevitability on other worlds, even those “next door” to us in space. But for others, the sensationalized findings of astronomers such as Lowell provided the impetus to launch their own delusional careers. One need only look at the dubious work of a one Leo Brenner to see how a colorful imagination can quickly run amok. Perhaps most importantly, it is through the sheer dedication of humble individuals, often from obscure backgrounds, that can most inspire amateur astronomers today. In this capacity, we shall look in detail at individuals such as Edward Emerson Fig. 4  An equatorially mounted Calver reflector dating to 1884 that sported a silver on glass reflector. Such technology revolutionized amateur astronomy. (Image courtesy of Denis Buczynski)

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Barnard, Charles Grover, and William Denning, who rose from obscurity to become some of the most active and productive observers in history. And then there are those observers who displayed almost superhuman visual acuity. One need only look at the extraordinary careers of the Reverend William Rutter Dawes or Sherburne Wesley Burnham to see how exceptional eyesight can set new precedents in resolution and visual perception. Finally, our exploration into the careers of the classical astronomers of old will help to teach us that there really is nothing new under the sun. Despite the drive to acquire telescopes that are more and more optically perfect, nothing of any substance has been discovered that was not seen by our illustrious telescopic ancestors. We still see the same belts and zones and spots and caps they saw on the planets using telescopes that many today would deem inferior. Though the chapters are arranged chronologically as far as possible, the reader can enjoy each one independently of all the others. Of course, with any work of this magnitude, some errors are bound to have crept in and are entirely of my own doing. Feel free to contact me should you notice one. All that remains for me to say is that I hope you will enjoy this whistle-stop tour of our shared astronomical history and come to appreciate, as I do, the enormous contributions our forebears made to both amateur and professional astronomy. Fintry by Glasgow, UK July 2018

Neil English

Acknowledgments

No book of this magnitude and scope could not be done in isolation. The author would like to thank many individuals for providing additional insights and useful images used to illustrate the text. In particular, he would like to extend his appreciation to Martin Mobberley, Denis Buczynski, Mike Oates, I.R.  Poyser, Gerard Gilligan, Kevin Schindler (Lowell Observatory), Dr. Jim Stephens (Mississippi, USA), Robert Katz, and John Nanson. A big thank you to Otto Piechowski for reading some of the earlier chapters of the manuscript and providing excellent feedback on their content. Special thanks are extended to Professor Wayne Orchiston, who kindly read and offered constructive criticisms on an earlier version of the entire manuscript. The author is also very grateful to Maury Solomon, Hannah Kaufman, and John Watson at Springer for believing in the project and granting an extension for the work to be fully completed. Last but certainly not least, he would like to thank his wife, Lorna, and two sons, Oscar and Douglas, for putting up with his long absences away from them in order to complete this project.

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Contents

1 Thomas Harriot, England’s First Telescopist����������������������������������������    1 2 The Legacy of Galileo������������������������������������������������������������������������������   11 3 The Checkered Career of Simon Marius ����������������������������������������������   29 4 The Era of Long Telescopes��������������������������������������������������������������������   35 5 Workers of Speculum������������������������������������������������������������������������������   65 6 Charles Messier, the Ferret of Comets ��������������������������������������������������   83 7 Thomas Jefferson and His Telescopic Forays����������������������������������������   97 8 The Herschel Legacy��������������������������������������������������������������������������������  105 9 Thinking Big: The Pioneers of Parsonstown ����������������������������������������  145 10 The Astronomical Adventures of William Lassell��������������������������������  165 11 Friedrich W. Bessel: The Man Who Dared to Measure������������������������  183 12 W. H. Smyth: The Admirable Admiral��������������������������������������������������  195 13 The Stellar Contributions of Wilhelm von Struve��������������������������������  203 14 The Eagle-Eyed Reverend William Rutter Dawes��������������������������������  209 15 The Telescopes of the Reverend Thomas William Webb����������������������  217 16 The Astronomical Adventures of Artistic Nathaniel Everett Green ������������������������������������������������������������������������������������������  231 17 Edward Emerson Barnard, the Early Years������������������������������������������  237 18 William F. Denning, a Biographical Sketch������������������������������������������  245 19 A Modern Commentary on W. F. Denning’s Telescopic Work for Starlight Evenings (1891) ������������������������������������������������������������������  255 20 The Astronomical Legacy of Asaph Hall ����������������������������������������������  321 xiii

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21 The Life and Work of Charles Grover (1842–1921) ����������������������������  329 22 Angelo Secchi, Father of Modern Astrophysics������������������������������������  347 23 John Birmingham, T. H. E. C. Espin and the Search for  Red Stars��������������������������������������������������������������������������������������������������  361 24 A Historic Clark Telescope Receives a New Lease on Life������������������  375 25 A Short Commentary on Percival Lowell’s “Mars as the Abode of Life” ������������������������������������������������������������������  381 26 The Great Meudon Refractor ����������������������������������������������������������������  401 27 A Short Commentary on R. G. Aitken’s The Binary Stars ������������������  415 28 S. W. Burnham: A Life Behind the Eyepiece����������������������������������������  431 29 Voyage to the Planets: The Astronomical Forays of Arthur Stanley Williams (1861–1938) ����������������������������������������������������������������  445 30 Explorer of the Planets: The Contributions of the Reverend T. E. R. Philips������������������������������������������������������������������������������������������  451 31 Highlights from the Life of Leslie C. Peltier������������������������������������������  457 32 Clyde W. Tombaugh, Discoverer of Pluto����������������������������������������������  479 33 A Short Commentary on Walter Scott Houston’s “Deep Sky Wonders” ������������������������������������������������������������������������������  499 34 A Short Commentary on David H. Levy’s The Quest for Comets��������  569 35 George Alcock and the Historic Ross Refractor ����������������������������������  595 36 Whatever Happened to Robert Burnham Junior? ������������������������������  603 37 The Impact of Mount Wilson’s 60-Inch Reflector��������������������������������  609 38 Seeing Saturnian Spots����������������������������������������������������������������������������  619 39 John Dobson and His Revolution ����������������������������������������������������������  625 40 The Telescopes of Sir Patrick Moore (1923–2012)��������������������������������  635 41 A Gift of a Telescope: The Japan 400 Project���������������������������������������  649 Appendix ����������������������������������������������������������������������������������������������������������  655 Index������������������������������������������������������������������������������������������������������������������  661

Chapter 1

Thomas Harriot, England’s First Telescopist

What is remarkable and possibly says much about Harriot’s personality is that he expressed only admiration for Galileo without the slightest trace of jealousy. –Allan Chapman

The mid-16th century was an era of profound social and political change in Europe; the Protestant Reformation swept across the kingdoms of the north, while in the southern reaches of the continent, Roman Catholicism still prevailed. The Renaissance juggernaut had introduced radical new ideas in the spheres of science, architecture, politics, art and literature, inspired by a palpable sense of nostalgia for the triumphs of classical antiquity. Knowledge, for so long the mainstay of the rich and powerful, was now being disseminated at a hitherto unprecedented rate to the ‘lower’ strata of European society, doubtless stoked by the invention of the printing press, which had empowered a new generation of scholars. And it was not just in Latin, the traditional language of the educated, but in the lingua franca of the various kingdoms, principalities and nation states of a new and self-confident Europe. This was the world that Thomas Harriot was hurled into, born sometime in the year 1560, in the county of Oxfordshire, England. Though he likely had a sister, his ancestry remains somewhat of a mystery to modern historians, and the first we hear of Harriot comes from his matriculation on December 20, 1577, from St. Mary’s Hall, a daughter house of Oriel College at the University of Oxford. In order to graduate, Harriot would have had to demonstrate a mastery of classical Latin and Greek, both spoken and written, as well as the Bible, the pillars of knowledge upon which all prospective Tudor scholars were required to assimilate. The contemporary reader can infer from this that Harriot’s family placed great value in education for its own sake and that they had sufficient wealth to prepare their bookish son for such a career, a circumstance still quite beyond the means of the vast majority of children. At St. Mary’s College Harriot absorbed himself in what we might now be called a classical education, with its strict adherence to Latinity, supplemented by rhetoric © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_1

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1  Thomas Harriot, England’s First Telescopist

Fig. 1.1  Thomas Harriot (1560–1621), England’s first telescopic astronomer. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:ThomasHarriot.jpg)

and structured debate, as well as the elements of Protestant theology and civil law. Any graduate worth his salt would have been expected to be able to discuss the pros and cons of complex ideas, in order to excel in the three principal career options open to him – jurisprudence, the Church and Parliament. But quite unlike the education of the ancient Romans, this educational program would also have included a thorough grounding in mathematics, geometry and Ptolemaic cosmology. And it was in these latter studies that Thomas Harriot would excel. It was very likely at St. Mary’s College that Harriot first came to the attention of Walter Raleigh (1552–1618), 8  years his senior and himself a graduate of Oriel College. By his late twenties, Raleigh had established a name for himself, both at home and abroad, as a naval commander, scholar and public showman, having the ear of the Virgin Queen herself. In this age, England had become a formidable maritime power with a decidedly imperious outlook, and Raleigh had high ambitions for the English Crown, to colonize the eastern Atlantic seaboard of North America. To make this a reality, though, Raleigh was always on the lookout for young and enterprising officers with a mathematical penchant, to conduct the surveys, the proper execution of various censuses, as well as the creation of maps of the new colonial territories. It was in this capacity that Harriot entered the employ of Raleigh, who bequeathed him an opulent apartment annexed to his own mansion at Durham House, on the banks of the River Thames (Fig. 1.1). Harriot’s first overseas expedition was to accompany Sir Richard Greenville to Virginia in the New World on board the Tiger, which departed from England in the spring of 1585. Greenville himself was under the auspices of Raleigh. Harriot’s duties included the thorough survey of the hinterland of the small, white settlements that had sprung up around the territory of the native Roanoke people, to learn the

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Fig. 1.2  Dancing Secotan Indians in North Carolina, very much like those encountered by Thomas Harriot. Watercolor painted by John White in 1585. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/Thomas_Harriot#/media/File:North_carolina_algonkin-rituale02.jpg)

language and customs of these native Americans and, if possible, to purchase land from them. This was not to be a bloody enterprise, however, with the usual spate of rapine pillaging. The land would be honorably acquired with a spirit of honesty and fair treatment, a circumstance that was aided substantially by the vastness of the New World and its sparse indigenous population. Raleigh had already brought two young men from the Algonquin nation, Wanchese and Manteo, back to England to immerse them in the cultural nuances of Elizabethan London, and, while there, they were given the freedom of Durham House before being repatriated under the aegis of Harriot, in their native Virginia. By all accounts, Harriot carried out his duties with great diligence and enthusiasm, learning the ‘queer’ tongue of the Algonquin and immersing himself in their rich culture and religious beliefs. Although one of the goals of such a mission was to take the Christian faith to the native Americans, it was not to be imposed on them. That said, Harriot found no shortage of Algonquins who embraced the new religion, finding that their beliefs were seamlessly assimilated into Christian doctrine (Fig. 1.2). Harriot produced a famous treatise, A Briefe and True Report of the New Found Land in Virginia, published in 1588, chronicling his dealings with the peoples of this new territory, and marking him out as arguably the father of modern ethnology.

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According to Dr. Allan Chapman, a renowned historian of science at the University of Oxford, Harriot could also be said to be the founding father of scientific education in North America. In his True Report, Harriot gave a lecture, presumably in the Algonquin language, to a native American audience, who were dumbstruck by the cleverness of the scientific instruments he brought with him from England: Mathematicall Instruments, Sea Compasses, the virtue of the Loadstone in drawing yron, a Perspective Glasse which shewd manie strange sightes. Burning Glasses, wide fire woorkes, Gunnes…Spring Clocks that seem to goe of themselves, and many other things that we had.

Some historians have used the accounts of the various optical devices described in his True Report as evidence that there may have been a ‘Tudor telescope,’ significantly predating those eventually acquired by Harriot (see below for more on this). Yet, as Chapman points out in his book, Stargazers, Copernicus, Galileo, the Telescope and the Church, this may be a classic case of reading too much into the literature: The strange sights and images which seemed to perplex and even alarm the Roanoke locals, I suspect, were probably no more than the facial and other distortions that anyone can see in a convex or concave mirror.

Thomas Harriot was an accomplished mathematician, one of the finest in England by all accounts. Most notably, perhaps, he introduced the symbols for less than (), which are used to solve equations. Harriot also did original work on the binomial theorem, which is an eminently useful technique for the expansion of algebraic expressions raised to any power. When Raleigh asked Harriot to investigate the science of gunnery in the 1590s, he applied a vector-based technique to resolve the projectile’s velocity into horizontal and vertical components and was able to deduce that its path fitted that of a parabola, an essentially modern analysis. He did however retain some outdated (and completely incorrect) ideas on motion, adhering to the ancient Aristotelian idea that heavier objects fall to Earth faster than lighter objects, for example. Having a lifelong interest in optics, Harriot formulated a theory of refraction in 1601, noting that when a ray of light passes from a thinner to a denser medium, the angle to which it is refracted from the point at which it enters the glass is always in the same proportion to the angle at which the ray first strikes the glass. This result, known more generally as Snell’s law, was independently discovered by the Dutch scientist Willebrord Snellus (1580–1626) in 1621. After Queen Elizabeth I died in March 1603, ending the line of the Tudors, James VI of Scotland ascended to the throne as James I, uniting the crowns of England and Scotland in the process. The new king, unlike Elizabeth before him, strongly disliked Sir Walter Raleigh. Indeed, just a few short months after the passing of Elizabeth, James I had Raleigh put on trial for treason. Though many scholars now consider the evidence against him to be specious at best, he was found guilty, sentenced to death, inexplicably reprieved from the gallows and condemned to ­spending the rest of his days under arrest in the Tower of London. Despite this change of

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events, Harriot visited Raleigh at the Tower on many occasions, remaining loyal to his friend and patron. It is important to remember that though Raleigh was imprisoned in the Tower, he still enjoyed considerable liberties, uncannily similar to Galileo’s ‘house arrest.’ A far cry from the dark, dank and rat-infested dungeons used for commoners, they were given comfortable lodgings, enjoying fine food and drink and freedom to roam within its walls, attend Church and carry out day to day investigations and studies. Even their families were permitted to live there. So, despite his ‘imprisonment,’ it was still possible for Raleigh to live out a reasonably fulfilled life from day to day. Harriot himself was not immune to the suspicions of the new regime, having been imprisoned in the Tower himself for 3 weeks, but after cross examination was summarily released in November 1605. Harriot’s loyalty was rewarded when Raleigh recommended him to Henry Percy, the Ninth Earl of Northumberland (1564–1632), who was also imprisoned for 17  years in the Tower for being a Catholic sympathizer and for his alleged involvement in the plot to destroy the Houses of Parliament in 1605. Fabulously wealthy, the ‘exotic’ Percy was rumored to have spent an unprecedented £50 a year on books (an enormous sum by today’s standards) and employed Harriot to carry on his scientific investigations. For this he was given a very generous stipend and access to Percy’s stately southern residence at Syon Park, Brentford, London, as well as a comfortable residence at Threadneedle Street in the city. Overnight, Harriot not only became financially independent but was now the richest mathematician in Europe, commanding a salary estimated to be ten times greater than the best paid university dons of the age! According to his 17th century biographer, John Aubrey, Harriot waded into all of the pressing astronomical questions of his day. “He had seen nine Cometes,” wrote Aubrey, “and had predicted Seaven of them, but did not tell how.” Intriguingly, according to Dr. Chapman, Harriot may have co-discovered the elliptical nature of the planetary orbits traditionally ascribed to the work of the German astronomer and mathematician Johannes Kepler. According to his friend and protégé, Sir William Lower, while pressing his master to compile a list of notable scientific achievements later in his life, left this tantalizing snippet: “…long since you told me as much [of Kepler], that the motions of the planets were not perfect circles,” and that the planets made their “revolutions in Ellipses.” What is certain, however, is that Harriot, being a geometer of some reputation and so intimately acquainted with the mathematics of orbits, would have had extensive correspondence with the other great intellectuals on the European continent, Johannes Kepler included. Furthermore, there is no evidence that Harriot promulgated the notion that he had arrived at the formula of the ellipse to explain the orbit of Mars. Indeed, in striking contrast to the vast majority of scientists of his time, Harriot never published anything after his True Report of 1588, which came as a source of considerable irritation to his patrons, who wished only to advance their own prestige on the back of his accomplishments, as well as to his friends, who watched in anguish as others trumpeted their ‘discoveries,’ many of which were probably best attributed to Harriot himself. This was a characteristic that was to set

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him apart from his contemporaries, who almost invariably conflated knowledge with power. Despite vigorous research efforts over many decades and centuries, historians of science cannot unequivocally attribute the invention of the first refracting telescope to any one individual. And though rumors abounded that there were telescopic devices significantly earlier than those that came on the scene in the early 17th century, it is undoubtedly the case that the enterprising spectacle maker, Hans Lippershey, based in the Dutch town of Middleburg, tried but ultimately failed to secure what would have been a lucrative patent in 1608 from the Dutch States General for the simple telescopes he constructed. As a result, the device, which consisted of a matched pair of convex and concave lenses arranged in a long, slender tube, could be fashioned and sold by anyone once the proverbial cat was let out of the bag. It is likely that Harriot acquired an early “dutch trunke” or “cylinder” from one commercial source in Holland early in the year 1609.

A Curious Aside: The Telescope of Leonard Digges Rumors have been circulated since the mid-16th century that the telescope was not invented in early 17th century Holland but in Elizabethan England, some half a century before. A telescopic device appears to have been constructed by the noted English polymath Leonard Digges (1515–c. 1559) as early as the first half of the 1500s and later reiterated by his son, Thomas Digges, in a communication dated to 1571: [H]is divine mind aided with this science of Geometrical mensurations, found out the quantities, distances, courses, and strange intricate miraculous motions of these resplendent heavenly Globes of Sun, Moon, Planets and Stares fixed, leaving the rules and precepts thereof to his posterity. Archimedes also (as some suppose) with a glass framed by revolution of a section Parabolicall, fired the Roman navy in the sea coming to the siege of Syracuse. But to leave these celestial causes and things done of antiquity long ago, my father by his continual painful [painstaking] practices, assisted with demonstrations Mathematical, was able, and sundry times hath by proportional Glasses duly situate in convenient angles, not only discovered things far off, read letters, numbered pieces of money with the very coin and superscription thereof, cast by some of his friends of purpose upon downs in open fields, but also seven miles off declared what hath been done at that instant in private places.

This intriguing tract, which appears on page 5 of the preface to his posthumously published book Pantometria (1571), provides the modern reader with an intriguing glimpse of a telescopic device made with lenses and mirrors. In a lively debate that took place in March 1993 organized by the Scientific Instrument Society (SIS) and held at Burlington House, London, Colin Ronan spoke in favor of the existence of such an early telescope, while the late Professor Gerard Turner, based at the Museum for the History of Science, Oxford, UK, provided a robust counterpoint. During the debate, a replica of the alleged Digges telescope was presented to all in attendance.

A Curious Aside: The Telescope of Leonard Digges

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Fig. 1.3  The author’s 6× achromatic spyglass used to corroborate Harriot’s observations. (Image by the author)

The device consisted of a simple biconvex objective lens, the light of which was incident to a focusing mirror that relayed the image to the eye. Mounted inside a wooden tube, the device magnified 11 times and did produce an enlarged image, but with a very narrow field of view, and was additionally plagued by chromatic aberration  – a consequence of using a singlet lens as an objective. There is, as yet, no consensus on whether such a telescope ever saw the light of day. Harriot and his assistant, Christopher Tooke, set up a telescope magnifying 6 times on the grounds of Syon Park, and on the clement evening of July 26, 1609, turned it on a five-day-old crescent Moon, immediately sketching what he saw. Various lunar ‘seas’ are included in these lunar portraits, including the Mare Crisium, Tranquilitatis and Fecunditatis, as well as some rugged lunar features situated along the terminator, which modern scholars have identified as Theophilus and Cyrillus. Curiously, this first sketch does not record any craters, although 6× is certainly large enough to resolve several of the more prominent ones. Out of sheer curiosity, in a separate investigation, this author used a modern spyglass with an uncoated, 1-inch diameter object glass, also having a magnification of 6×, in the wee small hours (01:30 h UT) of January 1, 2016, to record observations of the last quarter Moon and Jupiter, as they cleared the treetops in the eastern sky. Like Harriot’s telescope, the spyglass gave an erect, correctly orientated image but enjoyed a much larger field of view (approximately 4 angular degrees). Nonetheless, this author could confirm that many lunar craters can indeed be observed with a steady hand, as well as clearly showing various maria. Turning to Jupiter, then just a few degrees above the Moon, the telescope could clearly reveal four Galilean satellites all to one side of the planet (Fig. 1.3). It will come as somewhat of a surprise to the contemporary reader not acquainted with a Galilean telescope that, despite its very low magnifying power, its field of view was very restrictive – typically just over half the diameter of the full Moon! As a result, Harriot could not have seen the entire countenance of the lunar crescent even at the low magnifications his telescopes delivered. Incredibly, though, Harriot

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made many more drawings of the Moon, some of which display finer cartographic details than Galileo’s later drawings, but they were frustratingly left undated. When we take into account the radically different personalities of both Galileo (explored in the next chapter) and Harriot, we can see that both men had entirely different modi operandi. Harriot, having spent time in Virginia, was a draughtsman and well acquainted with mapmaking. His methods were slow and methodical. Harriot was categorically not seeking fame and fortune in the same way that Galileo was, and, according to Dr. Chapman, because Harriot had two high profile friends on ‘death row’ in the Tower, he had little desire to make himself conspicuous. By the closing weeks of 1609, Harriot dispatched Tooke, his able technician, to the residence of Sir William Lower at Trefenti, Carmarthenshire, South Wales, instructing him to fashion several other Galilean cylinders in order that he and his philosophical chums, a one Mr. Vaughan and Mr. Protheroe (and possibly a few others), could begin their own telescopic investigations of the Moon and other celestial bodies. The surviving exchanges between Harrriot and the ‘Carmartenshire philosophers,’ clearly unveil their avowed acceptance of the Copernican system, as well as Kepler’s elliptical theory of planetary orbits. This meeting may well be first known record of an astronomical society, the members of which were to confirm Galileo’s monumental telescopic work by observing the large Jovian satellites and the erstwhile “invisible” stars in the Pleiades. Over the next few years, Harriot was to complete his now famous Moon maps, as well as embarking on a detailed study of the Sun. His method involved observing the intensely bright solar disk, when it was near the horizon and veiled behind mist and thin cloud (the reader should, under no circumstances, attempt such an observation!). Harriot is credited as the co-discover of sunspots, recording them at or about the same time as Galileo, and possibly earlier than Christopher Scheiner (1573– 1650) and Johannes Fabricius (1587–1616), who themselves yielded additional evidence against the time-honored cosmology of Ptolemy (Fig. 1.4). Over the next 2 years, Harriot was to carry out some 450 observations of the Sun and its dark spots, never once claiming their discovery for himself, studying how they moved across its otherwise brilliant face, breaking up and sometimes even disappearing. Indeed, modern scholars were able to establish a solar rotation period of 27.154 days from Harriot’s drawings – uncannily close to the modern accepted value of 27.2753 days. This affirms the accuracy and attention to detail so central to Harriot’s methodology. According to Dr. Chapman, Tooke may have made improvements to the basic Dutch trunke, and referring to a study conducted by the distinguished historian of astronomy and cosmology, the late Professor John North (1934–2008) identified no less than six telescopes associated with Harriot and the ‘Trefentine’ philosophers, which ranged in power from 6× up to 50×. Tooke is likely to be among the first bona fide telescope makers in Britain, a tradition that was to be continued over the following centuries. Although Harriot embraced the Christian message from his youth, even writing the Lord’s Prayer in the Algonquin language, some scholars have suggested that he may have experienced a brief religious hiatus as he approached middle age.

A Curious Aside: The Telescope of Leonard Digges

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Fig. 1.4 Christoph Scheiner (1573–1650), the Jesuit priest and astronomer, with his telescope shown on his left. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ Christoph_Scheiner#/ media/File:Scheiner_ christoph.gif)

Doubtless, the revolution heralded by the application of the telescope to the celestial realm had raised new questions in the minds of his learned contemporaries. Why were the astronomical bodies puckered and imperfect? How did God create everything from nothing? Was His divine hand needed at every stage, from the formation of atoms to the completion of worlds? Was the allegory of the universe even attributed to a personal God or was it merely blind chance? These questions weighed heavily in the mind of Thomas Harriot. Dr. Chapman acknowledges that nothing firm can be adduced from Harriot’s surviving notes and correspondences, but he is inclined to the view that the world’s first telescopic astronomer re-embraced his Christian heritage in the final decade of his life, as evidenced by his 1615 correspondence with the king’s physician, Sir Theodore Mayerne, who assured Harriot of the certainty of the existence of one all-­ powerful God. From his days in Virginia, Harriot had taken to ‘drinking’ tobacco smoke, as his contemporaries had referred to it. Earlier physicians had hailed the new wonder drug as an effective remedy to counter the “dangerous moist humors of the body.” But three decades of heavy inhalation of tobacco smoke was to take its toll on Harriot’s health, and he developed a cancerous lesion on his nose. Because many tumors of this sort have a tendency to metastasize, spreading to other organs of the body via the lymph nodes, Harriot was arguably history’s first clearly attested tobacco-induced cancer victim, dying on July 2, 1621. He was laid to rest at his local Parish Church of St. Christopher-le-Stocks, located in the heart of the city of London. And while the church was razed to the ground by the Great Fire of 1666 and another resurrected on the original site by none other than Sir Christopher Wren (1632–1723), this too was eventually demolished in 1781  in order to make way for a grand new building that would became the headquarters of

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the Bank of England. In the 1970s, however, the gravestone dedicated to Thomas Harriot was recovered, and, in his honor, a new plaque carrying his gravestone inscription was unveiled inside the bank. It is difficult to crystallize the legacy of Thomas Harriot, being so far removed from him in time, but these words come to mind; learned, diligent, enterprising, kind, loyal, uncompetitive, humble and God-fearing. Despite not marrying and raising children, he lived a fulfilled life without a bad word to say about his fellow men, rendered all the more remarkable owing to his great wealth and lifelong connection with the rich and powerful.

Sources Chapman, A.: Stargazers: Copernicus, Galileo, the Telescope and the Church. Lion Books, Oxford (2014) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) North, J.: The Fontana History of Astronomy and Cosmology. Fontana Press, London (1994) Ringwood, S.: The Mystery of the Digges Telescope. Astronomy Now, pp. 53–57 (March 2018) Stevens, H.N.: Thomas Harriot: the Mathematician, the Philosopher and the Scholar: Developed Chiefly from Dormant Materials, with Notices of His Associates, Including Biographical and Bibliographical Dispositions Upon the Dispositions of ‘Ould Virgina’, Privately Printed. Chiswick Press, London (1900)

Chapter 2

The Legacy of Galileo

It is undoubtedly true that while there may have been a number of observers who had employed the telescope before Galileo, it is to him that we habitually turn to as the great pioneer of early telescopic astronomy. Galileo Galilei was born in the city of Pisa to his parents, father Vincenzo and mother Giulia Galilei, on February 15, 1564. A once independent city-state, Pisa had by now come under the administration of the so-called Florentine Diaspora of Tuscany and flourished throughout the Renaissance. The city enjoyed great wealth as a magnate for some of the richest merchants and bankers of the day. And as a university town, Pisa had also attracted some of the finest minds in Europe from the realms of art, architecture, theology, medicine and the natural sciences. Indeed, the other northern Italian cities, including Milan, Florence, Bologna, Venice and Genoa, enjoyed more or less equal status as self-governing city-states – much like the classical period of ancient Greece, but ruled by a curious assortment of dukes, kings, and prince bishoprics (Fig. 2.1). Galileo’s ancestors and surviving relatives were accomplished intellectuals, and the young man grew up to be a self-confident individual, receiving an excellent grounding in mathematics, musical theory and astronomy at the nearby monastery of Vollombroso. Although Galileo appears to have had an early calling to the religious life, intending at one time to be dedicated as a priest of the Roman Catholic Church, his father seemed to have other ideas about his eldest son’s future and removed him from the monastery so that he could prepare him for a career in medicine. But it was not at all to the tastes of this young son, who found the writings of the classical scholar of the Roman physician Galen to be strange and substantially outdated, seeing as 1,400 years had passed since the works of this revered scholar of classical antiquity were penned. Neither was Galileo’s argumentative nature much use to him in an intellectual environment that went out of its way to resist the march of progress. Truth be told, medical knowledge at that time was a hodgepodge of good science and quackery, and all the dissecting and overuse of flowery language probably bored the young Galileo senseless, whose mind was more cut out for precise calculation and mathematical certainty than any of his medical peers.

© Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_2

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Fig. 2.1  Galileo Galilei holding his telescope, portrait by Justus Sustermans (1636). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File%3AJustus_ Sustermans_-_Portrait_of_ Galileo_Galilei%2C_1636. jpg)

But medicine was a lucrative career and Vincenzo was quite displeased when he learned that his son had expressed a distaste for it. Instead, Galileo, now in his early twenties, longed to carve out an uncertain career as a mathematician. But in the end, Vincenzo, an accomplished musician in his own right, respected his son’s wishes and supported his retraining for a career in the ‘exact’ sciences. His progress was rapid, however, with him quickly distinguishing himself as the best mathematician in his class and being awarded a professorship at the University of Pisa in 1589 at only 25 years old! Being such a towering figure, it is easy to see why so many stories were cultivated about him, such as the famous tale where he became mesmerized by a swinging lamp in Pisa Cathedral that led him to deduce that the period of its swing was independent of the mass of the pendulum but only depended on the length of the string. Another story recounts how Galileo dropped cannon balls of different weights off the Leaning Tower of Pisa, discovering that they hit the ground at the same time, in sharp contradiction to the tenets of the time-honored Aristotelian physics. We have no idea about the veracity of these claims, since it was his devoted student, a one Vincenzo Viviani, who later became his biographer, and who first brought our attention to them. What is certain, though, is that Galileo was one of the greatest experimental physicists of his era, making valuable contributions to our knowledge of motion. Indeed, it was this experimental approach that distinguished

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Galileo from the medieval physicists who tended to analyze physical problems using Aristotelian ‘thought experiments.’ In this way, Galileo could rightly be called the father of the modern experimental method. Though of professorial rank, Galileo’s academic stipend was meager, and he resorted to supplementing his income by extending his tutelage to fee-paying private students. One of his patrons, a one Marchese Guido Ubaldo del Monte, used his influence to recommend Galileo to the vacant chair of mathematics at the more prestigious University of Padua, a post he enthusiastically took up in 1592, remaining there for the next 18 years. Here, in the Most Serene Republic of Venice, he enjoyed new freedoms that were not available to him at Pisa, as well as acquiring a circle of new and powerful friends. He also had access to the steady stream of new technological devices constantly streaming in from the nearby port of Venice, located only 24 miles from Padua. After studying their construction, he would often improve on the designs and sell them to interested parties, including the navy and military, which were always on the lookout for new gadgetry. A minor crisis precipitated in Galileo’s life in 1591, with the death of his father Vincenzo. Overnight he became the major breadwinner for his family, with a dependent mother, two unmarried sisters each requiring dowries, as well as funding the musical education of his younger brother, Michelangelo. But he made ends meet with his various technical enterprises as well as his role as a consultant to many private ventures. It was in Padua that Galileo met the love of his life, an attractive redhead from Venice, Marina Gamba. Although he never married her, she did bear him three children – two girls, Virginia and Livia, born in 1600 and 1601, respectively, and a younger son, Vincenzo (born 1606), named after his paternal grandfather. By the time he reached his fortieth birthday in 1604, it was becoming clear that Galileo was somewhat discontented. He had an uncanny knack of annoying and insulting people who didn’t see eye to eye with him, and as a consequence burned more than a few bridges. And despite having some very influential friends in high places, he could never rise above his station because of his seemingly endless financial difficulties. What’s more, he began to tire of his university teachings and having to deal with mostly mediocre students. What he truly longed for was financial independence so that he could get on with more ‘elevated’ themes allied to his eclectic research interests. This middle age discontentment with life was probably exacerbated by his first brush with the Holy Office in 1604, when he was accused of practicing a dangerous type of astrology. The debacle probably had its origin in his relationship with a Signor Silvestro Pagnoni, who had at one time been employed by Galileo as his secretary. For reasons that remain obscure, Pagnoni reported him to the Inquisition for casting so-called fatalistic horoscopes. Normal horoscopes were perfectly acceptable and indeed part of the cultural tradition of his times, but Galileo used his astrological knowledge to predict the death date of certain individuals. Such an activity was viewed as a type of divination in the eyes of the Inquisition and a distraction from worshiping the ‘true’ God. From that time on, Galileo’s work was never far from the scrutinizing eyes of the ecclesiastical authorities, as we shall see later.

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Galileo’s fortunes changed utterly and forever after the summer of 1609, when he heard of a curious new invention from Holland, an optical novelty that made distant objects appear closer. As we have seen earlier with the telescopic work of the English astronomer, Thomas Harriot, a great deal of mystery surrounded the invention of the telescope, and no one individual can legitimately lay claim to its discovery. Though the technology to contrive a telescopic device was available since ancient times, it was probably not conceived from any consideration of optical theory and most likely discovered serendipitously, perhaps during the idle investigations of childhood curiosity. When Galileo received news of the new optical marvel, he at once set to work reproducing his own. His first attempts yielded a device consisting of two lenses mounted at either end of a lead pipe, a device he called a cannocciale (little tube) but thereafter sought to make the instrument more powerful. The objective consisted of a convex lens, thicker in the middle and thinner at its edges, while the eye lens was concave in shape, thinner in the middle than at its edges and working in a similar way to modern opera glasses. The convex lens, with an aperture of slightly more than an inch, needed to have a focal length of 2 or 3 feet. Galileo used simple methods to arrive at this focal length by measuring how far from the eye the lens needed to be positioned in order to give a sharp image of a distant object. Galileo soon set about engineering and making improved versions of his telescopes. His earliest instruments only magnified eight times, but over time they became progressively more powerful. Soon he began grinding his own lenses and changing his arrays, extending their magnifying powers up to about 30 times more than normal vision, but, as we saw in the previous chapter, they all had a very narrow field of view. Fortunately for later scholars, Galileo had the presence of mind to leave a very detailed description of his telescopes in the opening pages of his first great work, the Sidereus Nuncius (Starry Messenger) in 1610, as he would again in his later work, Il Saggiatore (The Assayer), which was first published in 1623. In August 1609, Galileo ventured to Venice to show off one of his better telescopes to the dignitaries of the city, arranging for them to view the cityscape from the elevated vantage of the roof of St. Mark’s Cathedral and other high towers, where it apparently caused untold wonder among the viewers. The distinguished guests observed ships that were far out to sea a full 2 h before they became visible to the unaided eye. As a gesture of good will, he presented his cannocciale to the Venezia Serenissima as a gift. It was a clever move, for soon his professorship was confirmed for life and his salary increased to 1,000 florins. But others, more aware of day to day matters in the city, were rather dismayed at Galileo’s promotion, especially since a similar device was sold in Venice by a Frenchman for just a few lire (Fig. 2.2). Sometime in the late autumn of 1609, Galileo turned his cannocciale on a fouror five-day-old Moon. Though a precise date was never recorded, most modern scholars think this occurred around November 30. What Galileo observed shocked him; the Moon was not smooth as was believed since time immemorial but was jagged, broken and spotted with craters, mountains and deep valleys. His drawings

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Fig. 2.2  Galileo shows the Doge of Venice how to use the telescope. Fresco by Giuseppe Bertini (1858). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/File%3ABertini_ fresco_of_Galileo_Galilei_and_Doge_of_Venice.jpg)

were made as sepia wash paintings or as a printed woodcuts, the accuracy and attention to detail of which clearly revealing his advanced skills as an artist. The physical nature of the Moon as revealed by Galileo’s telescope flew in the face of the classical position of the lunar orb, which was believed to be a smooth, though tarnished, silvery ball. Galileo was not slow to make noise about this incongruity, later claiming in his Sidereus Nuncius that these lunar features were “never seen by anyone before me” and that a “great number of philosophers” had been flatly wrong in their belief that the Moon was “smooth, uniform and precisely spherical.” It is a curious historical fact that Galileo never made a comprehensive mapping of the Moon, a task he left to others. He was only concerned with revealing the salient features of the orb as it progressed through its phases. Perhaps he was too pressed with examining other objects to get pinned down on details. What we do know is that during the Christmas period of 1609 through January of 1610 he began

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systematic observations of the planet Jupiter, which was bright and well placed in the skies over northern Italy. Using his finest instrument delivering a power of about 30 diameters, what he saw was truly remarkable and, as he put it himself, was “never before seen since the creation of the world to our own time.” On his first night of observation he found Jupiter to be an oblate sphere, slightly stouter at the equator than at its poles, with three stars close to it, two to the east and one to the west. Enjoying a spell of clear winter nights, he watched in amazement as these stars appeared to change their positions with respect to the planet. He quickly deduced that they were circling Jupiter at various distances. Then on January 13, 1610, he observed a fourth ‘star.’ As the weeks went by, Galileo noted that the star nearest Jupiter appeared to be circling the planet faster than the others, with those located further out moving more slowly. What’s more, the satellites appeared to be moving in a plane that aligned itself with the planet’s equator. Galileo quickly grasped the astronomical and philosophical implications of such a discovery and how it was destined to change our perceptions of the nature of the planetary bodies forever after (Fig. 2.3). Firstly, no one had ever imagined that the planets might present themselves as sharp globes. The disk-like appearance of Jupiter as seen through Galileo’s telescope showed that Jupiter was a bona fide world in its own right. Secondly, and perhaps much more importantly, philosophers from classical antiquity until now had assumed, based on the best naked-eye evidence, that either Earth or the Sun (if you were a follower of Copernicus) was the sole center of rotation in the universe. Doubtless, the Copernicans had already accepted that the Moon had a rotation independent of the Sun-orbiting Earth, but the idea that the planets had satellites of their own seemed patently absurd to them, and yet anyone with a telescope curious enough to take the time to look would have been convinced of the truth of Galileo’s discovery. After the publication of Sidereus Nuncius in March 1610, Galileo returned to the telescope, but this time his attention shifted to a variety of other astronomical bodies. He recorded spots on the face of Sun and watched them slowly move across its face over time. In his Letter on Sunspots, dated to 1613, he reported his observations of Venus and how it underwent phases much in the same way as the Moon. It appeared largest as a thin crescent, gradually diminishing in angular diameter as it went through its phases and presented itself as a perfectly circular disk when it was at its smallest. To Galileo the changing angular size of Venus was related to its varying distance from Earth and, as such, provided powerful evidence in support of the Copernican theory that the planets orbit the Sun and not Earth. He also reported the curious appearance of Saturn. Unlike Jupiter and Venus, which did show a sharp disk, his telescope sometimes revealed to him a strange, elongated oval. At other times, Galileo saw a sphere with ansae (handles or ‘ears’) at either side of the planet. And occasionally, these Saturnian appendages completely disappeared! Writing to his friend Marcus Wesler at Augsburg, a high-ranking Roman Catholic intellectual, Galileo expressed concern that what he was seeing couldn’t possibly be true. Indeed, he wryly commented that it was as if Saturn had indeed consumed his

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Fig. 2.3  An excerpt of Galileo’s early notes on the wandering moons of Jupiter. This observation upset the notion that all celestial bodies must revolve around Earth. Galileo published a full description in Sidereus Nuncius in March 1610. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/File%3AGalileo_manuscript.png)

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own children, just as the ancient Roman myths recounted. What is more, the whole affair with Saturn raised the thorny question of whether the telescope could be a superior tool to pure deduction in the establishment of truths about the workings of the universe. Indeed, it was one of the issues used as ammunition against him in his later clash with officials of the Roman See. For now, though, the mystery surrounding Saturn had to wait until more powerful telescopes (Huygens, 1675) were able to resolve the issue. The ancient Greek astronomer Hipparchus (b. c. 190–120) had divided the stars in the firmament into six divisions of glory – what we now know as the magnitude scale. The brightest stellar luminaries were placed in the first magnitude, while those on the precipice of visibility were assigned to the sixth magnitude. But when Galileo turned his primitive telescope on the heavens, vast new shoals of stars came into view, far more than anyone had even thought possible. In particular, when he examined the Milky Way, or the Via Lactica as the ancient Romans had come to call it, he reported that it resolved into a “tight mass of stars.” Furthermore, his 6× telescope revealed less stars than one of 30×. Although it was true that some medieval theologian astronomers had openly speculated that the Milky Way was made up of innumerable stars, it could only remain a speculation until the advent of the telescope. In one fell swoop, the universe known to humankind was extended beyond measure. Galileo also visited a few well-known star clusters visible to the naked eye. When he examined the region known to us as the Sword Handle of Orion, he estimated that his telescope picked up about 600 new stars that were invisible to the naked eye, and when he scanned the belt stars in the Celestial Hunter he added a further 200 stars to the naked eye tally. Next he examined the Pleiades Cluster in Taurus, of which six or seven members can be clearly seen by the naked eye from a typical town. But his spyglass showed him about 40 new members. These he recorded in a sketch published in his Sidereus Nuncius. The same was true when he examined the Beehive Cluster (Praesepe) in Cancer. The philosophic and theological implications of Galileo’s telescopic adventures proved to be very unsettling for the Aristotelian academics, but not for Christians in the strictest sense. The trouble from the Church arose from those men within its ranks who had borrowed too heavily from the ancient Greek tradition, using it to inform their theological beliefs. Moreover, it must be stressed that none of what Galileo saw with his telescopes in any way contradicted Holy Scripture. What Galileo’s discoveries openly questioned was the perfection of the astronomical bodies themselves. Galileo was a keen observer of the solar surface, though he was almost certainly not the first telescopic observer to record dark spots on the Sun. That honor probably should go to the German astronomer, Johann Fabricius (1587–1616), who recorded them as early as the summer of 1611. An elaborate myth has been cultivated over the years that Galileo went blind from looking at the Sun through his telescope, but his own records of sunspot observations conducted over many years show that this was not so. His sight failed in his seventies after he had conducted several decades of solar observations. And unlike

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Thomas Harriot, who observed the rising Sun directly through clouds and mist, Galileo actually employed a projection method in his solar studies. This enabled him to accurately mark the position of sunspots and deduce their motion across the solar disk over many days and weeks. Seeing spots on the solar surface further contradicted the immutability of the heavenly bodies, in sharp contradiction to the strict adherents of Aristotelian dogma. Father Scheiner believed that the spots were not actually physically associated with the Sun but rather were ‘planetoids’ crossing in front of it. Others boldly proclaimed them to be mere optical illusions. Galileo believed otherwise and carefully prepared an argument that favored their physical association with a rotating Sun. He noted, for example, how the spots seemed quite two dimensional when they appeared at the center of the disk, but as they moved toward the limb, they became more linear, before disappearing altogether. A detached object, such as a ‘planetoid,’ on the other hand, would maintain its morphology irrespective of where it was projected onto the solar disk. This was powerful deductive reasoning, something Galileo was characteristically brilliant in expressing, and it was sound evidence upholding the idea that the spots were indeed physically associated with the Sun. By the end of 1610, Galileo was, without a shadow of a doubt, the most famous astronomer in Europe, and though officials at the University of Padua had made his lot more comfortable by granting him a substantial pay rise, he began to attract the attention of super-rich tycoons who were eager to share in the prestige of the Renaissance man who had transformed the science of astronomy forever. Thus, he was invited to the residence of the Grand Duke Cosimo II at Florence, where he was wined, dined and offered a very lucrative position as Court Astronomer to the Medicis. However, Galileo apparently didn’t like this title, suggested by the Grand Duke, since he had no ambitions to get involved in the drudgery of routine work. Instead, he brokered his own title, Grand Duke’s Philosopher, as it conveyed a more magisterial connotation more befitting of his substantial ego. He resigned his position as professor at Padua and took up residence in the opulent Villa delle Selve at Florence. Here, having the patronage of the Grand Duke of Tuscany, Galileo lived the life of a king, donning fine robes, golden rings and chains. Clearly, he had arrived. His newly elevated status allowed Galileo to converse with the rich and powerful across Europe, as well as senior dignitaries of the Roman Catholic Church. At first, things couldn’t have gone better for Galileo, for by Christmas 1610 his friend and admirer, Father Christopher Clavius, had informed him that astronomers at the papal observatory in the Vatican had confirmed the facts of his telescopic observations, but events in his private life began to catch up with him. Though having illegitimate children was all too common among princes and popes alike, their powers enabled them to hide them away, as it were, in the background, and be passed off as nephews or nieces and the like. But now that Galileo was Court Philosopher to the Medicis, he became increasingly aware that his familial circumstance could prove a source of embarrassment. Accordingly, he had his mistress, Marina Gamba, now in her middle age, packed off to Venice to look after the children. Her fate is still obscure, though. Official records from the period show that a woman by the same name died on August 12,

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1612, yet we know that a lady named Marina continued to look after his son Vincenzo, until he was old enough (probably at age eight or nine) to come and join his father at Florence. His two daughters were enrolled in a convent, where they took their future religious names, Sister Maria Celeste and Sister Arcangela. And in 1619, the Grand Duke legitimized Vincenzo, who became his father’s heir. The Collegium Romanum, the members of which included some of the greatest minds in Italy, invited Galileo to come to Rome in 1611 to discuss the telescope and the discoveries he had made with it. Here he found many admirers, including the distinguished astronomer Father Christopher Clavius, who listened carefully to what Galileo had to say but all the while refusing to believe that the surface of the Moon was truly battered and rough, as Galileo had disseminated. But others flatly refused to look through the telescope, and some even claimed to see nothing at all! The latter point might seem odd to us today but we must remember that looking through a crude Galilean telescope is not as easy as it may sound. As we saw in the previous chapter, the field of view in such an instrument is woefully narrow and requires some training in the placement of one’s eye. Before discussing the ‘Galileo Affair,’ as it has come to be known, it is important to state that the mythologized view of Galileo standing for truth and reason versus religion and superstition of the Roman Catholic Church is not at all accurate. Europe at the beginning of the 17th century was a rapidly changing and divided continent. Protestants fought Protestants, Catholics fought Catholics, and they fought each other. Neither was the Roman Catholic Church the seamless, monolithic body it was sometimes portrayed as. Truth be told, there were many within its ranks who longed for reform. Neither was it an Aristotelian boot camp, but had members who supported both sides of the intellectual divide. And while some minds could not be changed, many others remained open to the evidence as it became available. This is the environment that Galileo found himself, and much of the trouble he got into was self-inflicted. After all, he had an uncanny genius for falling out with people. Familial scandals and questionable astrology aside, Galileo had always enjoyed a good relationship with the Roman Catholic Church, and though never known for his piety, there is nothing in his writings that suggest that he held any unorthodox views. The controversy regarding heliocentrism erupted in 1613, when the poet and philosopher, Cosimo Boscaglia, argued that the idea that the Earth moved through space was contrary to the teachings of Holy Scripture. And while he accepted Galileo’s telescopic discoveries, he differed only in their interpretation. But things escalated in 1614 and 1615, when the Dominican friar, Tommaso Caccini, gave a sermon to his congregation in which he openly attacked the notion that our world moved through space, quoting passages from the Book of Joshua and Acts as ‘evidence’ to the contrary. This was followed not long after by an attack from an active member of the Catholic Counter Reformation, Niccolo Lorini, who used an article from the Council of Trent to uphold the plain interpretation of Scripture. Things came to a head on March 19, 1615, when Caccini denounced Galileo as a heretic to the Roman Inquisition. Truth be told, scientific matters were somewhat beyond the remit of this committee, set up back in 1232 to counter heresies of various kinds. Cross-examining sci-

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entists was not something it entered into lightly, but as the dissenting voices grew louder, something had to be done. Tensions moved up a gear when the Neopolitan Carmelite, Father Paolo Foscarini, published a pamphlet in 1615 entitled, Epistle Concerning the Pythagorean and Copernican Opinion on the Mobility of the Earth, in which he argued that the heliocentric hypothesis was not merely an intellectual construct or a calculating device but simply reflected the truth that Earth really does go around the Sun. Foscarini even used his own passages from the Bible to back up his claims. Going further than Galileo, Foscarini dispatched a copy of his epistle to Cardinal Roberto Bellarmine, a man of great intellectual standing and influence within the Vatican and far beyond. Bellarmine wrote a lengthy reply to Foscarini on April 12, 1615, in which he firmly set out his position on the matter. In essence, he expressed caution at re-interpreting a position that was upheld by the traditions of the Church Fathers, as well as the rich body of Greek philosophy dating back 1,500 years. Was it wise to throw the baby out with the bathwater, as it were, all because of one man’s sightings through a tube with two glass lenses? Bellarmine had no problem with folk discussing the Copernican system as a hypothesis, but the Council of Trent did take issue with anyone who interpreted scriptural passages that were contrary to the teachings of the Holy See. But Bellarmine also raised a third point in his correspondence with Foscarini (Fig. 2.4):

Fig. 2.4  Cardinal Robert Bellarmine (1542–1621), later beatified by the Roman Catholic Church. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File%3ASaint_Robert_ Bellarmine.png)

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2  The Legacy of Galileo If there were a real proof that the sun is the center of the universe, that the earth is in the third sphere (or third planet out after Mercury and Venus) and that the Sun does not go around the earth but the earth round the sun, then we would have to proceed with great circumspection in explaining passages of Scripture, which appear to teach the contrary, and rather admit that we did not understand them than declare false which is proved to be true.

Here Cardinal Bellarmine seems to have suggested that as of 1615 there was no absolute proof that Earth moves through space around the Sun and that he could not see a way that it would likely be proven true in the future. Galileo’s discovery of the lunar mountains, Jupiter’s satellite system and the phases of Venus might well be remarkable new natural phenomena, but they could not tip the balance in favor of a moving Earth. After all, the great pre-telescopic Danish astronomer, Tycho Brahe, openly declared in favor of a fixed, immovable Earth, and that was good enough for Bellarmine. What we do see in Bellarmine’s response to Foscarini, however, is a cool-headed approach that was neither fundamentalist in its outlook nor insensitive to the possibility of new insights being garnered that added to what had already been established. It had a certain degree of flexibility that was at once respectful of the cumulative wisdom of the ages and to the sacredness of scripture. The next development in the ‘Galileo Affair’ originated from a private dinner held at the Grand Duke of Tuscany’s residence in Florence, also attended by Galileo’s friend, a monk of the Benedictine Order, Benedetto Castelli. There they discussed Galileo’s recent discoveries and presumably also the debate about the moving Earth. Brother Castelli later (December 1614) set about summarizing the points that were raised in his discussion with the Grand Duke and sent a letter to Galileo for his feedback. This time, Galileo was not shy in coming forward, composing a response to the letter where he categorically came out in favor of the Copernican theory, emphatically stating that it was a statement of fact and not merely a hypothesis. He also raised the point that when Copernicus’ great work, De Revolutionibus, was first published back in 1543, he himself dedicated it to Pope Paul III and that it had not received any official condemnation from the Holy See. But here Galileo had taken things a bit too far in ascribing the lack of official condemnation of the Copernican theory by the Church as an argument for its acceptance. He was no theologian, and his knowledge of the Vulgate Bible was sketchy at best. Still, Galileo openly questioned the wisdom of reading too much into scripture when it came to addressing purely scientific questions. In this capacity, Galileo aligned himself with the comments of Cardinal Cesare Baronio (1538–1607), “The Bible teaches us how to go to heaven, not how the heavens go.” Circumstances had escalated enough that by the end of 1615, Galileo took it upon himself to go to Rome and convince Vatican officials of the truth of the Copernican system of cosmology, but also to get back at his perceived enemies, including Father Caccini and Niccolo Lorini, who had very publicly denounced him. This resulted in the establishment of a Holy Inquisition on February 19, 1616, to look into the matter and deliver its verdict. After due consideration of Galileo’s

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work, the Inquisition issued a report on February 24, concluding that heliocentrism was “foolish and absurd in philosophy,” because it contradicted the plain meaning of scriptural text. The next day, Pope Paul V ordered Cardinal Bellarmine to recommend to Galileo that he abandon the idea. It is important to stress that there was no bullying going on here. It was all conducted with the greatest respect for Galileo, who by now enjoyed great personal prestige as one of the towering scientific intellects of his age. He was even invited back to the Vatican to enjoy a private 45-min audience with Pope Paul V on March 11, 1616, where he was assured that no harm would come to him. Indeed, Galileo requested that Cardinal Bellarmine summarize the position of the Church in regard to heliocentrism and accordingly was issued a certificate indicating that Galileo had done nothing wrong in advancing the case for a moving Earth but that, based on the best evidence available at that time, it was not wise to promulgate this notion of cosmology. So, with hindsight, we could say that the Church was wrong for the right reasons, since, at that time, it was not proven beyond all reasonable doubt that Earth was orbiting the Sun. In saying this, the Church was merely defending scholasticism. Galileo clearly respected the verdict of the Church but did not accept its conclusions and set about finding more evidence to bolster the Copernican system. In 1616 he may have been told to keep quiet on Copernicanism, but in the years that followed, a web of new events was to raise the stakes for Galileo. In 1618, three bright comets appeared in the sky eerily coinciding with the outbreak of the 30 Years’ War. Father Orazio Grassi of the Jesuit College wrote up a paper about them, describing them as bodies that were burning, moving in curved paths, and located beyond the Moon. To Grassi, the dynamics of cometary motion best fitted Tycho Brahe’s geo-­ heliocentric system. This is essentially a geocentric model; Earth is at the center of the universe. That is, the Sun, Moon and stars revolve around Earth, and the other five planets revolve around the Sun. Nonetheless, as the American philosopher of science, Thomas Kuhn (1922–96) remarked back in 1957, it could be shown that the motions of the planets and the Sun relative to Earth in Brahe’s system were mathematically equivalent to the Copernican heliocentric system and could be achieved simply by holding the Sun fixed instead of Earth. In 1623 Galileo’s supporter and friend, Cardinal Maffeo Barberini, ascended to the papacy, becoming Pope Urban VIII. Barberini was a completely different personality to Paul V, however, being very familiar with the astronomical issues of his age, and he was also a great admirer of Galileo besides being his friend. The election of Barberini to the papacy seemed to assure Galileo of support at the highest level in the Church. Indeed, Galileo dedicated his new work, Il Saggitore, or The Assayer, to his old friend. The title page of The Assayer is adorned in the crest of the Barberini family, featuring three busy bees. In The Assayer, Galileo weighs the astronomical views of Grassi and finds that they lack a certain rigor. Galileo’s polemical tone was common at the time. However, the book was read with delight at the dinner table by Urban VIII. Indeed, in 1620, Barberini dedicated a Latin poem entitled Adulatio Perniciosa in Galileo’s honor. Furthermore, a Vatican official, Giovanni di Guevara, declared that the contents of The Assayer were free from any unorthodoxy.

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Galileo insisted that physics should be mathematical and not descriptive in the case of the traditional Aristotelian tenets. According to the title page of the work, he was the philosopher or physicist of the Grand Duke of Tuscany, not merely a mathematician. Physics, or natural philosophy, spans the gamut from processes of generation and growth (represented by a plant) to the physical structure of the universe, represented by the cosmic cross-section. Mathematics, on the other hand, is symbolized by telescopes and an astrolabe. This is the book containing Galileo’s famous statement that mathematics is the language of science. Only through mathematics can one achieve lasting truth in physics. Those who neglect mathematics are fated to wandering endlessly in a ‘dark labyrinth’: Philosophy is written in this grand book – I mean the universe – which stands continually open to our gaze, but it cannot be understood unless one first learns to comprehend the language and interpret the characters in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometrical figures, without which it is humanly impossible to understand a single word of it; without these, one is wandering around in a dark labyrinth.

Although The Assayer contains a magnificent polemic for mathematical physics, ironically its main point was to ridicule Father Grassi’s paper on comets. In The Assayer, Galileo mistakenly countered that comets were an optical illusion. Grassi was correct about comets after all. But while the contents of The Assayer were a source of delight for many within the Church, it was considered incendiary to others, particularly some powerful individuals within the Jesuit order. It was around the mid-1620s that Galileo, now in his sixties, began thinking about a new literary work that would hammer home his deep conviction that the heliocentric ideas of Copernicus were correct. These ideas crystallized around a new form of argument – dialogue, or more specifically, Dialogue Concerning the Two Chief Systems of the World, Ptolemaic and Copernican. To enact this, Galileo decided to stage a fictitious conversation, set in Venice, between two philosophers and a layman, taking place over 4 days of discussion. The first philosopher, Salviati, argues for the Copernican position and presents some of Galileo’s views directly. He is called the “Academician” in honor of Galileo’s membership in the Accademia dei Lincei and named after a real figure, Galileo’s friend, Filippo Salviati (1582–1614). The other philosopher, Simplicio, is a dedicated student of the ancients, Ptolemy and Aristotle, in particular, and accordingly presents the traditional views and the arguments against the Copernican position. He, too, is supposedly named after a real person, Simplicius of Cilicia, a 6th century commentator on Aristotle, but it was suspected that the name was a double entendre, as the Italian for “simple” is semplice. The character of Simplicio seems to have been modeled on two contemporary but conservative philosophers, Lodovico delle Colombe (1565–1616?), by now one of Galileo’s fiercest detractors, and Cesare Cremonini (1550–1631), an erstwhile academic colleague of Galileo at Padua, who had flatly refused to look through his telescope. Indeed, Colombe became the ringleader of a group of Florentine opponents of Galileo (Fig. 2.5). It is important to remember that there was nothing especially new in the Dialogue, but the arguments he presented were put together in a novel and masterful way, writ-

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Fig. 2.5  Frontispiece of Galileo’s 1632 master work, Dialogue Concerning the Two World Systems, Ptolemaic and Copernican. (Image courtesy of Wiki Commons. https://en.wikipedia.org/ wiki/File%3AGalileos_Dialogue_Title_Page.png)

ten in Italian, the lingua franca of the man on the street and not Latin, which made it intelligible to as wide an audience as possible. What we see in the Dialogue is Galileo’s blatant bias against Sagredo, who was meant to be completely impartial, and Simplicio, who is ridiculed time and time again. Armed with his new treatise, Galileo set out for the Eternal City, having the full backing of the new Grand Duke of Tuscany, Ferdinand II, and was even allowed access to his personal litter and its bearers. What he sought was the imprimatur of the Catholic Church. Completed in 1630 the Dialogue, in its opening pages, urges the discerning reader to weigh the evidence carefully for and against the two cosmological systems, but it is rather obvious that Galileo holds a candle for the Copernican model from the outset and leads the reader in this direction. It was a work of brilliant scientific propaganda. Urban VIII assigned Niccolo Riccardi, of the Order of Preachers, to the task of examining the work. An easygoing and gentle character by all accounts, Riccardi was not however especially well trained in astronomy, and records show that Galileo harried him to give into his request. By July 1631, Riccardi finally gave his imprimatur and the book was allowed to go to press in Florence, where it first appeared in printed form in February 1632. Within weeks of the book appearing, a cacophony of dissenting voices was heard across Europe, and as a result, the publisher was ordered to cease the sales of the manuscript on October 1, 1632. Galileo was once again summoned to the Vatican for questioning, but made excuses on

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account of his advancing age (he was now in his 68th year) and failing health. The Vatican, however, was having none of this. Once again, the Grand Duke lent Galileo his comfortable litter to travel the 200-mile road trip to Rome in early 1633, and he was placed on trial in April of the same year. By this time, Galileo’s old friend, Urban VIII, with whom he had enjoyed many personal conversations over the years, was now visibly angry with him for refusing to let his views on the Copernican system of the world lie. A jury was assembled to hear Galileo’s defense of the ideas promulgated in his Dialogue, convening on a number of occasions between April and June of 1633. In the end, it pronounced Galileo to be a heretic for continuing to advance the heliocentric hypothesis and was sentenced to imprisonment on June 22. However, on the following day, he was commuted to house arrest at Arcetri, near Florence. Finally, the Dialogue was banned. In retrospect, had Galileo embraced Tycho Brahe’s geo-heliocentric model, it would have calmed the Jesuit opponents in the jury because it could accommodate the Copernican theory. However, Galileo, for inexplicable reasons, never entertained Tycho’s earlier conclusions. In 1616, Galileo was ordered in a precept by the Church to cease defending heliocentrism in any way, and Galileo, who was supposed to be a devout Catholic, promised to obey. And as we have seen, 15 years later, he sought an audience with the newly appointed pope to publish a review of the heliocentric and geocentric views and was granted permission. However, he never mentioned the precept during his request, and this omission led to Galileo’s conviction and house arrest. Rather than being a monumental clash between science and religion, Galileo’s conviction was actually a legal matter he handled poorly. We should thus refrain from portraying Galileo in an exalted light, as some kind of martyr for the scientific cause and more of an intellectual rebel – who was eventually proved right – who fought a political battle with the Church and came out the worse for wear as a consequence. In short, any lawyer worth his salt would have advised Galileo not to push the matter. Despite his encounter with the Catholic Church, there were many within its ranks that still held him in high esteem. For example, on his way to Arceti, a long-time admirer of his work, Ascanio Piccolominni, then Archbishop of Sienna, with the express permission from the Pope, invited Galileo to stay with him for a short holiday at his residence before moving on to Arcetri. This is evidence of the goodwill within the Church and a strike against any over-zealous scholar who might have claimed that the Roman See was an inhumane, monolithic organization. Arcetri was also very near to the monastery in which Galileo’s daughters lived and worked, and it came as some delight to them to hear that their world-famous father would live out his last days in close proximity to them. His son, Vincenzo, also joined him there, as well as his pupil and later biographer, Senior Vincenzo Viviani. Here Galileo would resume his scientific work freely and unhindered, discovering new phenomenon with his telescopes, including the libration of the Moon (resulting from an incomplete tidal locking with Earth, allowing up to 59 percent of its surface to be seen), among other things (he is also reported as having seen Uranus but did not see its significance). But the old man’s eyes rapidly failed in his seventies, and so he was forced to give up his telescopic observations of the heavens.

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Revered by many, Galileo was visited by many learned men at Arcetri, including the English philosopher, Thomas Hobbes, and the poet John Milton (who later immortalized him in his Paradise Lost). Galileo continued to receive visitors until 1642 when, after suffering fever and heart palpitations, he gave up the ghost on January 8, 1642, aged 77, the same year that Isaac Newton entered the world. The Grand Duke of Tuscany, Ferdinando II, made active plans to have him buried in the main body of the Basilica of Santa Croce, next to the tombs of his father and other ancestors, and to erect a marble mausoleum in his honor. But these plans were abandoned after Pope Urban VIII and his nephew, Cardinal Francesco Barberini, protested, because Galileo had been condemned by the Catholic Church for “vehement suspicion of heresy.” He was instead buried in a small room annexed to the novices’ chapel at the end of a corridor from the southern transept of the basilica to the sacristy. Galileo was reburied in the main body of the basilica in 1737 after a monument had been erected there in his honor. Sometime during this move, three fingers and a tooth were removed from his remains. One of these fingers, the middle digit from his right hand, is currently on exhibition at the Museo Galileo in Florence, Italy. As one of the earliest telescopic observers, Galileo will be remembered for opening the window on the universe that has not shut since. In many ways also, he was the father of modern physics by insisting that nature’s laws were inherently mathematical in nature and could best be couched in those terms. Soon, everyone who was anyone in Europe wanted a telescope to see what Galileo saw. And the Jesuits, to their credit, helped spread the message of the telescope to the far-flung corners of the Earth. In some way, this author cannot help but think that every time we point our telescopes toward the heavens, we honor the great Italian scientist who started the fire with such passion and vehemence. Seen in this light, Galileo Galilei ushered in a revolution that has yet to set on the modern world.

Sources Chapman, A.: Stargazers; Copernicus, Galileo and the Telescope. Lion Hudson, Oxford (2014) Drake, S.: Galileo. Oxford University Press, Oxford (1992) Ferngren, G.B.: Science and Religion. Johns Hopkins University Press, Baltimore (2002) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Hoskin, M. (ed.): The Cambridge Concise History of Astronomy. Cambridge University Press, Cambridge (1999) Kuhn, T.S.: The Copernican Revolution. Harvard University Press, Cambridge (1957) Mayer, T.F.: The Roman Inquisition’s Precept to Galileo 1616. http://journals.cambridge.org/ action/displayAbstract?fromPage=online&aid=7892276&fileId=S0007087409990069 North, J.: The Fontana History of Astronomy and Cosmology. Fontana Press, London (1994) A Contemporary Look at the Galileo Affair. https://evolutionnews.org/2017/09/the-galileoaffair-a-durable-myth/

Chapter 3

The Checkered Career of Simon Marius

The phenomenal success of Galileo Galilei with the telescope spread like wildfire across the nation-states of Europe, with the result that nearly every astronomer was keen to get his or her hands on such an instrument to make new discoveries in the starry heavens. One of the earliest “wannabees” was the German astronomer Simon Marius. Born Simon Mayr (later Latinized to Marius) on January 10, 1573, in Gunzenhausen in the region of the Markgrafschaft of Ansbach (Bavaria, south Germany), where his father served as mayor of the city in 1576. From 1586 to 1601, he studied on and off at the Markgrafschaft’s Lutheran academy at Heilsbronn. And it was during his studies here, beginning around 1594, that he became interested in embarking on a career in astronomy and meteorology (Fig. 3.1). In 1596 Marius wrote a tract on the comet that appeared in the sky that year, and in 1599 he published a set of astronomical tables. The quality of his researches resulted in his appointment as court mathematician of the Markgrafschaft of Ansbach in 1601. In this opulent milieu Marius continued to publish annual prognostications until his death. One of his first acts as the Markgrafschaft’s mathematician was to travel to Prague to learn of Tycho Brahe’s observational techniques and to gain familiarity with his instruments. Unfortunately, Brahe died that same year, and Marius’ stay in Prague lasted only 4 months. But he did meet David Fabricius there, who helped consolidate his interest in the science of the heavens. After this, he sojourned to Padua to study at the university there, where he quickly became politically active in the student association calling itself the “German Nation,” acting as its chairman from 1604 to 1605. In 1602 Marius extended his tutelage to Baldessar Capra, a wealthy student from Milan, in mathematics and astronomy, but there is also evidence that he supplemented his income by practicing medicine. Capra and Marius both observed the nova of 1604 together, and with Marius’s help Capra published a book on the new ‘guest’ star. In 1607 Capra published under his own name Galileo’s instruction manual on the sector, which was circulated in the form of a manuscript, and which led to Capra’s expulsion from the university. It appears that Marius played an important

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Fig. 3.1  Engraved image of Simon Marius (1573–1624), from his book Mundus Iovialis, 1614. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ Simon_Marius#/media/ File:Houghton_GC6_ M4552_614m_-_Simon_ Marius_-_cropped.jpg)

role in this plagiarism, but he had returned to his native land in 1605 and so temporarily escaped vilification. In Italy, however, Marius’s reputation was tarnished by this fraud, and by certain other questionable practices as head of the German Nation. Upon his return from Italy, Marius settled in the city of Ansbach and accepted the post of court mathematician, marrying Felicitas Lauer, the daughter of his publisher. In 1609 he published the first German translation (from the original Greek) of the first six books of Euclid’s Elements. But Marius’ most memorable (and controversial) research involved the telescope. In the fall of 1608, at the Frankfurt Fair, Marius met an artillery officer who tried to sell him a spyglass. Intrigued, the two set about reproducing the device by using spectacle lenses, but it was not until at least a year later that Marius obtained instruments good enough for astronomical observations. Marius’s oldest surviving observation of Jupiter’s satellites dates from the end of December 1610. In his prognostications for 1612, which was completed in March 1611, Marius stated that he had observed Jupiter’s moons beginning in December 1609 and was busy determining the periods of the satellites. In 1614 Marius published the fruits of his research on Jupiter in a book entitled Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici (“The Jovian World, discovered in 1609 by means of the Dutch Telescope”), in which he claimed that he had observed Jupiter’s moons beginning as early as the end of November 1609 and furthermore had begun recording his observations on December 29. That said, Marius had adopted the Julian calendar and so the date corresponded to January 8, 1610, on the Gregorian calendar.

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Since Marius did not publish any observations, as Galileo had done in his Sidereus Nuncius, it is impossible to verify Marius’s claim. His reputation was, however, not the highest. Galileo responded to Marius’s claim in his Assayer of 1623, beginning with a complaint about those who had tried to pass off his discoveries and then took aim at Marius: Of such usurpers I might name not a few, but I shall pass them over now in silence, as it is customary for first offenses to receive less severe punishment than subsequent ones. But I shall not remain silent any longer about a second offender who has tried too audaciously to do me the very same thing which he did many years ago by appropriating the invention of my geometric compass, despite the fact that I had many years previously shown it and discussed it before a large number of gentlemen and had finally made it public in print. May I be pardoned this if, against my nature, my habit, and my present intentions – I show resentment and cry out, perhaps with too much bitterness, about a thing which I have kept to myself these many years. I speak of Simon Marius of Gunzenhausen; he it was in Padua, where I resided at the time, who set forth in Latin the use of the said compass of mine and, appropriating it to himself, had one of his pupils print this under his name. Forthwith, perhaps to escape punishment, he departed immediately for his native land, leaving his pupil in the lurch as the saying goes; and against the latter, in the absence of Simon Marius, I was obliged to proceed in the manner which is set forth in the Defense which I then wrote and published. Four years after the publication of my Sidereal Messenger, this same fellow, desiring as usual to ornament himself with the labors of others) did not blush to make himself the author of the things I had discovered and printed in that work. Publishing under the title of The Jovian World, he had the temerity to claim that he had observed the Medicean planets which revolve about Jupiter before I had done so. But because it rarely happens that truth allows herself to be suppressed by falsehood, you may see how he himself, through his carelessness and lack of understanding, gives me in that very work of his the means of convicting him by irrefutable testimony and revealing unmistakably his error, showing not only that he did not observe the said stars before me but even that he did not certainly see them until two years afterwards; and I say moreover that it may be affirmed very probably that he never observed them at all.

After making an argument about the inclinations of the orbits of the satellites to the ecliptic, Galileo turned his attention to the date on which Marius claimed to have discovered the satellites: Next, notice the craft with which he tries to show himself prior to me. I wrote in my Sidereal Messenger of making my first observation on the seventh of January, 1610, continuing then with others on the succeeding nights. Along comes Marius, and, appropriating my very observations, he prints in the title page of his book and again in the opening part of his work that he had already made his observations in the year 1609, trying to give people the idea that he was first. Now the earliest observation that he produces as made by him is the second one made by me; yet he announces it as made in the year 1609. What he neglects to mention to the reader is that since he is outside our church and has not accepted the Gregorian calendar, the seventh day of January of 1610 for us Catholics is the same as the twenty-eighth day of December of 1609 for those heretics. So much for the priority of his pretended observations.

Nevertheless, at the behest of Johannes Kepler, Marius named the moons after the lovers of Zeus (the Greek equivalent of Jupiter): Io, Europa, Ganymede, and Callisto. Galileo, predictably enough, steadfastly refused to accept Marius’ names and instead invented the numbering scheme that is still used today, alongside proper moon names. In accordance with this scheme, the Galilean satellites were assigned

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numbers based on their proximity to their parent planet and increase with distance. Hence, the moons of Io, Europa, Ganymede and Callisto were designated as Jupiter I, II, III and IV, respectively. In his Mundus Jovialis, Marius also noted that the satellites varied in speed, the faster ones orbiting nearer the giant planet, a clue to the nature of the underlying gravitational forces at work. Marius’ telescope showed that even the distant stars appeared as disks, and he interpreted them as such; a notion that persisted for much of the 17th century. Indeed, it was only after a proper theory of diffraction was formulated that these ideas were firmly put to rest. Nonetheless, Marius used this as evidence that the stars were not as far away as would have been required to bolster the Copernican worldview. In retrospect, Galileo probably went a bit overboard in these accusations, in much the same way as he had countered his critics within the Catholic Church, for it appears certain that Marius was independently observing Jupiter’s moons by December 1610. It is probably true that had Marius not delayed publishing his telescopic findings until 1614, many of the aspersions cast by Galileo might not have been expressed. Mundus Lovialis does, however, contain a telescopic discovery the priority of which has never been disputed: On December 15, 1612, Marius was the first to observe the Andromeda Nebula, which could not be resolved into stars, describing it as a “flame seen through horn.” Apparently, Marius was not aware that this object had been seen previously by medieval Persian astronomers and described by Al Sufi as early as 964 a. d. From several remarks in his works, it appears that Marius was a militant Lutheran. He kept up his correspondence with David Fabricius and Kepler’s former teacher, Michael Maestlin, both of whom were self-proclaimed Lutherans. Furthermore, Marius even defended Tycho Brahe’s Lutheran world system on scriptural as well as astronomical and physical grounds. Besides his annual prognostications, Marius published in his later years a book on the comets of 1618 and, posthumously, a work on Ptolemy’s position circle. In a letter written in summer 1611 Marius gave mention to his observations of Venus, and from  August of the same year, he had been observing sunspots. By November, he noticed that the movement of the sunspots and therefore the equatorial plane of the Sun is tilted relative to the ecliptic. Maintaining active observation of the Sun via projection, in 1619 Marius first suggested that the appearance of sunspots was periodical. It is interesting to note that while Marius was undoubtedly an observer of the most important astronomical discoveries of the early 17th century, he opposed the heliocentric view of the cosmos and favored the Tychonic system. Perhaps it was Marius’ staunch belief in this system over that of the Copernican counterpoint that gave him pause to accept the reality of the eclipsing satellite phenomenon with Jupiter. Indeed Marius claimed to have arrived at the Tychonian mechanism independently of Brahe after reading the work of Copernicus during the winter of 1595– 1596. One can only surmise that had Marius lived a longer life, he might have vindicated himself from the slurs Galileo aimed at him. Alas, it was not to be. He died in Ansbach after a brief illness on January 5, 1625, less than a week before his 52nd birthday.

Sources

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To this day, Marius’ work is overshadowed by the accusation of plagiarism, even though it was demonstrated by a jury convened in the Netherlands in the early 1900s that he had, in fact, conducted much of his research entirely independently of others. In more recent times, Simon Marius was honored by the astronomical community by the naming of a lunar crater after him in 1935, the 41-km-diameter Marius Crater. And in 1979 a region on Jupiter’s moon, Ganymede, was named Marius Regio. In 2014, asteroid (7984) Marius was named in his honor, discovered on September 29, 1980, by Czech astronomer Zdenka Vavrova at the Kiel Observatory, and provisionally designated 1980 SM.

Sources Simon Marius: Mathematician: Medical Practictioner: Astronomer. http://www.simon-marius.net/ index.php?lang=en&menu=2 The Mundus Jovialis of Simon Marius. http://articles.adsabs.harvard.edu/full/1916Obs....39..403 Drake, S.: Galileo. Oxford University Press, Oxford (1992) Hockey, T. (ed.): The Biographical Encyclopedia of Astronomers. Springer, New York (2009)

Chapter 4

The Era of Long Telescopes

The telescopes used by Galileo and his contemporaries were not very powerful, more suited in fact to terrestrial viewing than astronomical observation. The design could only be used to give a rather limited magnification (of the order of 30×). The images were also plagued with optical imperfections owing to the rather crude design of the earliest lenses. Perhaps the greatest issue to overcome was the unequal refraction of the different colors of visible light by glass. Blue light was refracted more strongly than red rays, with the result that the position of focus was different for different colors of light. The consequence of this phenomenon is that bright objects were surrounded by a veritable kaleidoscope of color – chromatic aberration – that reduced image sharpness and contrast. Moreover, the field of view was woefully small, making aiming difficult to achieve. Small wonder, therefore, that astronomers began to search for ways of improving the design of their telescopes, and the immediate solution was to configure better lenses with longer focal lengths. Although plane glass several inches in diameter was available for luxury window panes from the beginning of the 17th century, its optical quality was only so-so, owing to the presence of air bubbles, striae and other artifacts. But by the 1650s onward, glass makers were able to craft mirror plate glass blanks of up to 1 foot across with sizable regions that were relatively free of such artifacts. A diamond could be used to cut out a decent-sized section of say 3 or 4 inches in diameter, and because the glass was up to 1-inch thick, it was easier to figure into the geometric shape of a lens without fear of shattering. By changing the curvature of the lens, focal lengths of any size could be made, from 10 feet to 200 feet or more; the gentler the curvature the longer the focal length. And because the image scale increases with focal length, higher magnifications could be coaxed out of them. Suddenly powers of 100× or even 200× could be achieved with the standard eyepieces of the day. In addition, by extending the focal length of these lenses, the effects of chromatic and other aberrations could be greatly reduced. One of the earliest telescopists to go beyond Galileo was his compatriot, lawyer and amateur astronomer Francesco Fontana (1580–1656). Using an improved © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_4

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Fig. 4.1  Engraving of Francesco Fontana (ca. 1580–1656). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Francesco_Fontana#/ media/File:Francesco_ Fontana.png)

t­elescope at his home in Naples, with an object glass of longer focal length to that of the Galilean telescope, he was able to make out the first detail on the planet Jupiter – just two bands hugging the equator. It wasn’t much, but at least it showed that the planets were not bland and featureless, as Galileo had opined. In 1636, Fontana reported that Mercury also goes through phases, like Venus and the Moon. And in August 1638, he observed Mars and recorded a bizarre egg-shaped world with a dark central spot! Clearly, whatever he saw, it was not a clear image of Mars and must have been derived from aberrations in his telescope, perhaps as a consequence of over magnifying the image. In 1645 his imagination got the better of him, when he claimed to have observed a satellite of Venus. He would not be the first to make such a claim, but no Cytherean moons have ever been confirmed (Fig. 4.1). Although the optical principles of light grasp and resolution were not yet formulated, bigger lenses gave brighter and more detailed images, allowing astronomers to see finer and finer detail. By the mid-17th century, opticians from across Europe were refining such techniques, driven by the growing demand of astronomers to peer ever farther into the mysteries of the firmament. And many astronomers simply made their own lenses. One of the earliest pioneers in this brave new world was Jan Hewelke, who Latinized his name to Johann Hevelius. Born in Dantzig (then part of Poland) on January 28, 1611, Hevelius grew up in a wealthy family of merchant-­ brewers that flourished throughout the Renaissance. His family, of which there were at least ten known children, were the producers of the famed Jopen beer sought after (and still brewed today) all over Europe.

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Fig. 4.2 Johannes Hevelius (1615–1683), one of the earliest observers to make use of very long focal length non achromatic refractors. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Johannes_Hevelius#/ media/File:Johannes_ Hevelius (close-up).jpg)

Hevelius’ family were a cultured lot, and the boy received the best education money could buy. He was introduced to astronomy by his German schoolmaster, Peter Kruger, who was also an avid observer and instrument maker, and after completing his education in some of the finest institutions in Europe, including a degree in jurisprudence from the University of Leiden, he settled down in the city of his birth and lavished considerable sums of money in acquiring the finest optics available at the time. His observatory would have its own workshops, observing platforms, library and even his very own printing press! Hevelius also had the distinction of arguably being the first astronomer to live out his entire life in the telescopic age! (Fig. 4.2) After his mentor, Peter Kruger, passed away in 1639, Hevelius vowed to dedicate himself full-time to astronomy, handing over the day to day business affairs to his wife, Katharine Rebeschke, whom he married in March 1635. The first task he set himself was to re-chart the heavens and improve on Tycho Brahe’s 1602 catalog of 777 stars. He proceeded to build a lavish observatory spread over the rooftops of several of his own houses at Danzig, and installed standard wooden instruments such as sextants and quadrants, but to his chagrin, he found that they were not accurate enough. He thus replaced them with higher quality metallic instruments and also went about buying a telescope. But after a period of research he found that he

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Fig. 4.3  Map of the Moon by Johannes Hevelius from his Selenographia (1647), clearly showing the lunar libration. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/ Selenography#/media/File:Hevelius_Map_of_the_Moon_1647.jpg)

could not purchase one of sufficiently high quality and so was compelled to build his own. Being a skilled artisan in his own right, Hevelius set about grinding and polishing his own lenses. Everything was done in situ. His first instrument had an objective aperture of just 1.5 inches, with a focal length of 12 feet and delivering a magnification of about 50 diameters. This is the telescope Hevelius employed to make his celebrated map of the Moon, conducted during the period in which his great observatory was being built and equipped, and which is now immortalized in his celebrated work, Selenographia, which appeared in 1647. As a punctilious self-publicist, Hevelius lavishly illustrated the work on the highest quality paper then available. Selenographia is two inches thick and consists of 43 one-foot diameter drawings of the lunar surface along with a number of full Moon maps. Analogous to Robert Hooke’s Micrographia, Selenographia also provides excellent illustrated details of the equipment used by Hevelius in his observatory, including details of their construction and manufacture. The various lunar features – craters, mountains and seas (maria) – are given classical Greek and Roman names. Selenographia became the standard lunar reference for astronomers for the next century (Fig. 4.3).

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Of particular interest to the reader is that Selenographia was not produced with a view to selling it to a mass readership. Instead, he dispatched copies of the highest quality to distinguished astronomers and patrons of science across Christendom. And even though a devout Lutheran, Hevelius even gifted a copy to the new Pope Innocent X in Rome, who came to appreciate its scientific and artistic significance. Rarely have we seen such a splendid example of munificence in the annals of science. Hevelius’ observatory was finally completed in 1657, at which time he resumed work on stellar positional measurements. But in 1663, disaster struck, when his wife died suddenly, which forced him to take hold of the reins of his family business and domestic duties that she had carried out so well. But in 1664, Hevelius was to remarry. His new bride, though 36 years his junior, was a match made in heaven. Not only did Catherina Elisabetha (1647–93), look after his children and assist him in running the business, she also expressed an unusual interest in astronomy and came to assist her husband as he made his nightly vigils of the heavens. She also became a very accomplished observer in her own right. In this capacity, Catherina Elisabetha (with the possible exception of Hypatia of Alexandria) is arguably the first woman in history for which there is a visual record of her engaging in active astronomical research. Historians of science now ascertain that Hevelius acquired at least eight telescopes of steadily increasing power during his long career. The first, as we have seen, had a small aperture of only 1.5 inches and a working focal length of 12 feet. But these were followed by instruments of gradually increasing focal length – 30, 40, 50, 60, 70 feet and finally, an instrument with a 150-foot focus, which was so large that it had to be set up outside the city proper. He significantly reduced the weight of his monstrous telescopes by leaving them in an open structure of narrow wooden spars, with circular rings at intervals acting as spacers, which were individually blackened to serve as bona fide optical stops. The objective lenses he employed also grew commensurately in size, with the largest having an aperture of 8 inches! The objective was mounted in a tube at the top of a large pole, elevated by notches carved into it, and adjusted by a group of assistants using an elaborate system of ropes and pulleys (Fig. 4.4). It is difficult to imagine how any observations of value could be made with such unwieldy telescopes. Some astronomers, such as Sir Edmond Halley (1656–1742), even went so far as to pronounce such instruments useless. The slightest breeze could set its various parts swinging wildly in mid-air, and even though the optical quality of such ‘aerial’ telescopes were, at best, mediocre, a dedicated observer could make out details on the Moon and planets that would have had Galileo jumping for joy! Hevelius carried out numerous lunar, planetary and solar observations. Intriguingly, his drawings of Saturn do not show any significant advances on Galileo’s records, depicting it as a globe with two crescent-like handles. Hevelius carefully recorded movements of the satellites of Jupiter, their configurations, eclipses, latitudes and periods of revolution. On November 22, 1644, he succeeded in observing the phases of Mercury, confirming Fontana’s earlier observations. His many solar records were also published as appendices to his 1647 Selenographia, his 1668 Cometographia, as well as his 1679 Machinae Coelistis.

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Fig. 4.4  Woodcut of Hevelius’ 46-m (150-ft) focal length telescope. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Johannes_Hevelius#/media/File:Houghton_Typ_ 620.73.451_-_Johannes_Hevelius,_Machinae_coelestis,_1673.jpg)

Hevelius devoted the first book of the Cometographia to the great comet of 1652, showing, for example, that its parallax was not great enough for it to be sublunary. Later Hevelius wrote on the physical constitution of comets, but without much insight, favoring, for instance, a disk-like (as opposed to a spherical) structure for the head. In books VI, VII and XII of the Cometographia Hevelius collected a considerable body of information, especially concerning the comets of the two preceding centuries. Hevelius understood comets to be condensed ‘planetary exhalations,’ supposing them to be linked with the material responsible for sunspots. When he questioned the physical causes of cometary motions he was barely able to pass beyond a vague and qualitative explanation in terms of impulses provided by interacting exhalations. Hevelius did study sunspots in great detail, though, using his observations to determine the solar rotation period to a much greater accuracy than any of his predecessors. He also coined the name “faculae” for the bright regions surrounding sunspots, a term that survives to this day. His sunspot observations, covering the time period 1642–1679, are of particular importance as they span the first part of the “Maunder minimum” of solar activity, as well as the time period immediately preceding it.

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Optical science, as we understand it today, was still in its infancy in the mid-17th century, and we witness in the practices of Hevelius, activities that would raise more than a few eyebrows today. For instance, he spent much time with a micrometer measuring the diameters of spurious stellar disks, believing them to be the true angular sizes of the stellar bodies (modern optical theory predicts that the size of the Airy disk gets smaller and not larger as the resolving power of the telescope increases). Still, he put the micrometer (modified from an original design by Huygens) to good and appropriate use to obtain better measures of the angular diameters of the bright planets. For his devotion to astronomy and his diligent observational work, Hevelius was elected to the Royal Society in 1664, and in 1666 was offered the directorship of the newly erected Paris Observatory, an offer he respectfully declined. But at the zenith of his career, another disaster was to beset Hevelius. A terrible fire razed his beloved rooftop observatory to the ground on September 26, 1679, completely destroying a further 40 houses in the surrounding area. Though no one was officially blamed for the debacle, it was rumored that a disgruntled servant of Hevelius deliberately started it. Many of the invaluable records he had stored at the observatory were lost, save a manuscript of his new star catalog, which was allegedly recovered by his eldest daughter. But all was not in vain. Many came to his rescue, including King Louis XIV of France and King Jan III Sobieski of Poland, who awarded Hevelius a generous lifelong stipend and much financial support for him to build a new observatory in order that he might continue his astronomical work. Though very grateful and moved by the kind gestures of these great monarchs, he was now 68 years old, and he could not help but feel that times would never be the same again. And yet, remarkably, Hevelius’ most important and lasting contribution to astronomy was still in his future. In mapping the brightest stars of the heavens, Hevelius felt compelled to add new constellations to those already recognized and celebrated since antiquity. Living in an age where classical mythology was still an important part of the educational system, Hevelius grew discontented with the many obvious gaps between the then accepted constellations and new patterns that his mind’s eye painted. So Hevelius went about inventing a dozen new ones. These novel constellations were as follows: Asterion: one of the hunting dogs Cerebrus: the three-headed hound of Hades Chara: the second hunting dog Lacerta sive Stellio: the spotted lizard Leo Minor: the little lion Lynx: the lynx Mons Maenalus; Mount Maenalus Scutum Sobieski: Sobieski’s shield Sextans Uraniae: the astronomical sextant Triangulum Minus: the small triangle Vulpecula cum Anser: the fox with the goose These constellations were presented in a new work, published posthumously by his wife in 1690, some 3 years after he died (at age 76). This new work, which has

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come to be known as Prodromus Astronomiae, consisted of a catalog containing a total of 1,564 stars divided up among 54 constellations, and arranged alphabetically under their names and by stellar magnitude within constellations. These were listed with their latitude, longitude, right ascension and declination, some of which were miscalculated. The same work outlined a list of discrepancies between the positional measurements of Tycho Brahe and his own, as well as a short treatise on spherical trigonometry. In the years that followed, some of these constellations were merged together, such as Chara and Asterion, which became known as Canes Venatici (the hunting dogs). King Sobieski’s name was also dropped and simply became known as Scutum, the celestial shield. Lacerta sive Stellio was shortened to Lacerta, and Sextans Uraniae whittled down to Sextans. Others were dropped entirely, such as Cerebrus, Triangulum Minus and Mons Maenalus. Although Hevelius does not belong to the highest ranks of theoretical astronomers, he could well be described as the doyen of mid-17th-century telescopic observers. He was the last great astronomer to derive new data using old-fashioned instruments designed for the naked eye. Indeed Hevelius’ character might well be judged from the sentiments expressed on the engraved title pages of his posthumously published Prodromus Astronomiae, two of which stand out: “Not by words but by deeds” and “I prefer the unaided eye.” The non-achromatic telescope found new expression in Holland, with the work of the brothers Huygens – Christiaan (1629–1695) and his elder sibling, Constantijn (1628–97). As young lads, they were already well versed in the experimental sciences, having enjoyed a comfortable upbringing in the opulent estates of their father, Sir Constantijn (1596–1687), at Zuilichem in The Hague. Constantijn senior was a distinguished scholar, musician, and diplomat for the Dutch Republic, and was knighted by King James I of England. He even discovered a promising new artist named Rembrandt von Rijn. Constantijn was also a keen amateur astronomer, but it was his younger son, Christiaan, who would go down in history as an astronomer, mathematician and a physicist of great repute (Fig. 4.5). Christiaan’s first brush with telescopes came when he was 24  years old. He wanted an instrument that would show something of the wonders he had read about in the popular astronomy books of the day, which, by now were already casting Galileo in a somewhat revered light. Huygens was particularly drawn to optics and became fascinated with the lens grinding techniques of the distinguished German optician, Johann Wiesel, based at Augsburg, and who had established a solid reputation supplying objective lenses to clients across Europe. Wiesel advised Huygens that he could purchase a ready-made telescope with one of his lenses from a dealer in Arnhem, Holland. His time with that telescope must have been a success, for within a year of its purchase the Huygens brothers began fashioning their own lenses. It was important to get the highest quality optical glass for their projects, and there is some evidence that they sourced it, at least initially, from London and Amsterdam, but also from a local glass house in Hertogenbosch. They took basic instruction in lens making from well-established opticians such as Jan van der Wyck from Delft and Caspar Calthoff (who later moved to England) in Dordrecht as well

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Fig. 4.5 Christiaan Huygens (1629–1695), pioneer of physics and astronomy. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Christiaan_Huygens#/ media/File:Christiaanhuygens4.jpg)

as Nicholaas Hartsoeker. However they found that there was a limit to the information these lens makers were willing to divulge, as they had an overriding instinct to protect their trade secrets, even taking them to the grave! Nonetheless, the Huygens brothers had learned enough to begin working their own optical glass. Their first task was to construct metal molds with perfect spherical shapes into which they would pour the molten glass in such a way as to avoid air bubbles and other artifacts that would reduce their optical quality. Next, they transferred these glass spheres to a lathe and slowly ground them into the right shape (plano-convex). Soon, they were churning out high quality lenses that could be mounted in suitably designed tubes. Success came early for Christiaan when he mounted a 2-inch diameter objective with a focal length of 23 feet and delivering a power of about 50 diameters. With this instrument he was able to discern that the surface of Mars was not of a uniform color but instead possessed some darker markings. His careful drawings showed that he had seen one of the most prominent surface features on the planet, the Syrtis Major. By following these dark markings as the planet turned on its axis, Huygens estimated that its day was 24.5 h long – very close to the modern accepted value. He also used the same telescope to examine the mysterious glowing nebula in the Sword handle of Orion (M42). After viewing the featureless planet Venus, he correctly surmised that it was a world permanently shrouded in cloud (Fig. 4.6). On the evening of March 25, 1655, using a telescope with a focal length of just over 11 feet and with an eyepiece of 3.1 inches, delivering a power of about 43×, Huygens began examining the planet Saturn. His keen eyes immediately picked up a fairly bright ‘star’ near to the planet, but over a series of good clear nights, he was

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Fig. 4.6  Huygens’ telescope without tube. Picture from his 1684 Astroscopia Compendiaria tubi optici molimine liberata (compound telescopes without a tube). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Christiaan_Huygens#/media/File:Aerialtelescope.jpg)

able to deduce that this star was in fact a Saturnian satellite  – Titan. Huygens announced his discovery of Titan in the form of a letter written on June 13, 1655, addressed to Professor J. Wallis at the University of Oxford. In this letter Huygens disclosed to him that he had made ‘a discovery’ with his new 11-foot telescope. However, he didn’t disclose the nature of that discovery but, as was the rather odd

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custom in those years, he concealed it in the form of an anagram. Indeed, Huygens waited until March 15, 1666, to reveal his new discovery to the world! The elucidation of Titan fanned the flames of Huygens’ curiosity. Continuing his study of Saturn over the next couple of years and using more powerful telescopes of his own design, he was able to finally deduce what no one had ever done before; Saturn, he stated, was surrounded by a “ring, thin, plane, nowhere attached and inclined to the ecliptic.” Huygens had uncovered the salient physical features of Saturn’s glorious ring system and solved the riddle that had eluded both Galileo and Hevelius, owing to the inferior quality of their telescopes. It would, however, be wrong to think that Huygens unraveled this mystery merely from observations alone. We now know that he had carefully studied the drawings of the planet made by many of his contemporaries and predecessors and, together with his own observations of Saturn, used his formidable skills of intuition to hit on the correct answer (Fig. 4.7). All of this work was summarized in Huygens’ Systema Saturnium, first published in 1659. In this publication, he provided a perfectly logical explanation for the apparent disparity in the visual appearance of Saturn as recorded by a number of astronomers over the decades. The axis of Earth and Saturn are tilted with respect to each other, he insisted, and, as it orbits the Sun, the degree of tilt varies. At its maximum tilt, the open ring could be seen, but when the tilt was minimized, the rings would be observed almost edge-on and thus would be almost imperceptible to an Earth-bound observer. Systema Saturnium also described the discovery of the planet’s giant moon, Titan, adding further evidence in support of the Copernican system (Fig. 4.8). In the same volume, Huygens also openly speculated on the plurality of worlds and the possibility that the Creator might have made them to be inhabited also. This he saw as a natural extension of the Copernican principle and closely allied to it, the principle of plenitude. Indeed, Huygens considerably expands on these ideas in his Cosmotheoros (1695). He argued that extraterrestrial life is neither confirmed nor denied by the Bible, and questioned why God would create the other planets if they were not to serve a greater purpose than merely being admired from Earth. Huygens postulated that the great distance between the planets signified that God had not intended for putative beings on one body to know about the beings on the others, and had not foreseen how much humans would advance in scientific knowledge. This was intellectual dynamite embracing the new spirit of the age. Small wonder, therefore, that Holland was seen as the new Mecca, where free thinkers could fully explore scientific and theological questions without any hindrances from the princes of the Church. “The world is my Fatherland,” Huygens boldly declared, “and science my religion.” After these distinguished publications hit the printing press, the Huygens brothers appear to have ceased making telescope lenses for the best part of 20 years. The reason for this was Christiaan’s invitation by King Louis XIV to join a team of prestigious astronomers in the newly established Paris Observatory. It was an offer he couldn’t refuse, seeing as he would get a chance to work with the finest visual observers of his day, including the Italian, Giovanni Domenico Cassini, and the

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Fig. 4.7  Huygens’ explanation for the aspects of Saturn, Systema Saturnium, 1659. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Christiaan_Huygens#/media/File:Huygens_ Systema_Saturnium.jpg)

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Fig. 4.8 Huyghens’ drawing of the Syrtis Major, Nov. 28, 1659. (Image courtesy of the New York Public Library/ Science Source. https:// www.sciencesource.com/ archive/ChristiaanHuygens-Mars-Map– 1659-SS2576879.html)

Dane, Ole Rømer, about whom we shall have much more to say later in the chapter. So, in taking up his position in Paris in 1666, Huygens was elected into the prestigious French Académie des Sciences and remained there for the next 15  years, where his genius would blossom beyond all measure. Indeed, there was hardly an area of natural sciences where he did not leave his mark. It was during his stay in Paris, that Huygens greatly improved a special eyepiece for telescopes, which is now commonly known as the Huygenian. This eyepiece consists of two positive lenses with different focal lengths, separated from each other by a small distance. The new ocular rendered an improved and wider field of view than any eyepiece conceived of before this time, and it fully removed lateral color aberration. Here also did Huygens undergo fundamental work in physics, developing the wave theory of light, deriving the formula for the period of a pendulum and formulating a working equation for centripetal force. He also wrote a new treatise on probability theory (Fig. 4.9). In one curious investigation, Huygens began to wonder how far away the stars really were, as their parallaxes had been far too small to measure with even the best instruments of the age. Noting the brightness of the Dog Star, Sirius, Huygens had several holes of differing diameter bored into a thin, brass plate. Holding such a device up to the noonday Sun, he asked himself which hole best matched his brightness estimate for Sirius. The hole he chose was 1/28,000th the apparent size of the Sun, so he reasoned that Sirius must lie at least 28,000 times farther away from the Sun. That comes to about half a light year. The real value, as we now know today, is 8.8 light years. Indeed, had Huygens known that Sirius was intrinsically brighter than our Sun – something he had not considered – he would have come up with almost the right answer!

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Fig. 4.9  The design of the Huygenian eyepiece. (Image courtesy of Tamasflex)

Huygens was also the first astronomer in history to call our attention to atmospheric seeing. He noted that when the air was turbulent, stars would coruscate more wildly than on calmer nights. Furthermore, he noticed that bad seeing caused the images to ‘boil’ in the telescope, while on the best nights the images would be cleaner and steadier. He even cautioned beginning telescopists to refrain from condemning their instrument too hastily until they had thoroughly investigated their local seeing conditions. Sadly, as we shall discover later in the book, many amateurs today display shocking ignorance of their local seeing conditions, leading to sometimes wildly exaggerated reports on the performance of their instruments! Huygens was also the inventor of the pendulum clock and suggested ways of determining longitude during long sea voyages. Although not fully successful, Huygens had shown in principle that an accurate shipboard clock would be able to tell the time in your home port, while the rising and setting of the Sun and the distant stars would specify the local shipboard time. The difference between the two would provide your longitude. Huygens could not however fashion a chronometer stable enough to keep accurate time on board ship, but later innovations by the English inventor and horologist John Harrison in the 1760s made this possible. It was in 1681 that Huygens returned to Holland after suffering a bout of depressive illness while in Paris, and once again took up the task of making new lenses along with his brother, Constantijn. By this time, Christiaan had gained far more experience in practical optics, having used the telescopes at the Paris Observatory, including some high quality aerial telescopes with lenses fashioned by the famous Italian optician Guissepe Campani (1635–1715). Born into a peasant family in 1635, Campani was an Umbrian from Castel San Felice near Spoleto. He soon went to Rome to seek his fortune with his two brothers, one of whom was a cleric, the other a clockmaker, and probably studied optics at the Collegio Romano, becoming supremely skillful in grinding lenses. His optical wares, all made in Rome, found customers all over the emerging nations of Europe. Indeed, Campani was known as the best maker of optical instruments of his age. The pope and his nephew, Cardinal Flavio Chigi, remained among Campani’s most important patrons, but he also won considerable favor with Ferdinand II, Grand Duke of Tuscany. On his return to The Hague, Huygens had learned quite a bit about Campani’s lenses, and together with his brother, would only select the best glass substrates and leave the figuring to well-trained technicians. They insisted on doing the final ­polishing of the lenses themselves, however, and this was done using a special kind of paper. Together, they fashioned some monster lenses up to 8 inches in diameter and with focal lengths of up to 123 feet.

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The exceptionally long focal length of these objects necessitated mounting them aerially, that is, the objective was mounted inside a small tube fixed to a mast. The eyepiece end was connected to the objective via a rope that could be yanked into position, allowing the optics to come into alignment. But this was easier said than done, especially in the dark. One solution hit upon by Huygens was to employ a lantern to illuminate the object glass. The glass would reflect some of that lantern light, and he would look through the eyepiece to search for this reflection, which brought the lenses into line. How ingenious! With a bit of practice, Huygens became adept at aligning the optics quickly so that he could get on with observing. Remarkably, though they fashioned many objectives, a fine collection of which are on display at the Museum Boerhaave in Leiden, only a single complete telescope by Huygens has survived until the present day. Known as the Campinine telescope, it had a focal length of 5 meters and delivered an upright image (using a novel multi-element eyepiece of his own design) with a magnification of 43×. The tube could be collapsed into a smaller unit, and five drawtubes were pulled out when in use. Huygens built it to amuse curious passersby. It is also known that Huygens did not normally employ the full aperture of his objectives but often stopped them down around the edges. He had apparently concluded from careful testing that the quality of the image improved by masking off the outer part of the lens. In one known example, a 63-mm lens was only used at 35 mm! Huygens was arguably the first astronomer to try to minimize the chromatic aberration inherent to the non-­ achromatic refractor design by having the eyepiece lenses gently smoked, thereby acting as a kind of color filter. It is difficult to overestimate Christiaan Huygens’ contribution to astronomy and the natural sciences, and his legacy lives on into the 21st century. A crater on Mars, a mountain on the Moon and an asteroid are all named in his honor. In 2005, ESA’s Cassini mission to Saturn launched the Huygens probe, which entered the smoggy atmosphere of Titan before landing successfully on its frozen, rocky surface and beaming back images of this alien world – itself larger than the planet Mercury. The non-achromatic telescope was also used most successfully by the Italian-­ born astronomer Giovanni Domenico Cassini (1625–1712), who himself worked with Huygens for many years. The son of Jacopo Cassini, a Tuscan, and Julia Crovesi, he showed an early interest in studying the heavens, and soon dabbled in astrology. As a boy, Cassini read widely on this subject, soon becoming proficient in the dark art. But it was this extensive knowledge of astrology that eventually led to his calling to become an astronomer. In 1645 the Marquis Cornelio Malvasia, a senator of Bologna with a great interest in astrology, invited Cassini to Bologna and offered him a position in the Panzano Observatory, which was then under construction. Most of their time was spent calculating newer, better and more accurate ephemerides for astrological purposes using the rapidly advancing astronomical methods and tools of the day (Fig. 4.10). In 1648 Cassini began his employment at Panzano, working with Cornelio Malvasia (1603–1664), inaugurating the maiden part of his astronomical career. Here Cassini was able to complete his education under the scientists, Giovanni Battista Riccioli and Francesco Maria Grimaldi. In 1650 the senate of Bologna

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Fig. 4.10 Giovanni D. Cassini (1625–1712). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Giovanni_Domenico_ Cassini#/media/ File:Giovanni_Cassini.jpg)

appointed Cassini to the chair of astronomy at the University of Bologna. Here he had access to a few of Campani’s non-achromatic telescopes, and he immediately put them to good use, refining the length of the Martian day to 24 h and 40 min – just 1 min off the modern accepted value! He was also the first to record a significant amount of detail in Jupiter’s atmosphere, identifying the main bands and zones on the planet. By studying the kinematics of a small spot on the planet, Cassini was able to provide the first estimate of the length of a Jovian day: 9 h and 56 min, essentially the accepted modern value. Cassini remained in Bologna for 20 years until the Sun King’s influential minister, J. B. Colbert, ‘headhunted’ him to come to Paris to help establish the prestigious Observatory there. Cassini departed from Bologna on February 25, 1669, to become its first Director. In his first few years at the Paris Observatory Cassini set to work advancing planetary science. In September 1671, he used a 17-foot focus non-achromatic telescope with an objective lens by Campani to discover a second satellite of Saturn, a body later named Iapetus. This was followed by the discovery of a third, Rhea, using the same instrument. In 1672, using observational data collated by his colleague, Jean Richer (1630–96), he accurately determined the distance to Mars via triangulation, thereby refining the dimensions of the Solar System and the value of the astronomical unit (the Earth-Sun distance). He also created improved ephemerides for Jupiter’s Galilean moons, and discovered the so-called light-time effect, which his co-worker, Ole Rømer, used to calculate the velocity of light in 1675.

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Fig. 4.11  Ole Rømer (1644–1710) at work at the Paris Observatory. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Ole_R%C3%B8mer#/media/File:Ole_R%C3%B8mer_ at_work.jpg)

Specifically, a discrepancy was observed for the time between the eclipses of the innermost large satellite, Io, increasing when Earth was moving away from Jupiter and decreasing when Earth was approaching it. Over 6 months, there were a total of 102 eclipses of Io, giving a maximum delay of 16.5 min. In a stroke of genius, Rømer interpreted this as the difference in the times needed for the light to travel between Jupiter and Earth. He obtained a value of 214,000 km/s compared to the current value 299,792 km/s. That said, the diameter of Earth’s orbit was not accurately known at this time, and there was also an error in the measurement of the delay. Nevertheless, Rømer had employed the non-achromatic refractor to establish a far-reaching fact: that the speed of light is finite! Light takes time to travel through space! (Fig. 4.11)

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In March 1684, Cassini utilized more powerful Campani telescopes of 100 and 136 feet focus to uncover two further satellites of Saturn, Tethys and Dione. The long focal lengths of these lenses necessitated that they be mounted aerially. But while these instruments sound monstrous to us today, they were dwarfed by the efforts of other lens makers. Constantijn Huygens, for example, fashioned a lens with a 210-foot focal length and the French physicist, Adrien Azout, possessed objective lenses of unimaginably long focal lengths – 300 and 600 feet. Azout even proposed employing a magnification of 1,000 or more diameters in the hope of seeing animals on the Moon! Most of the time, however, Cassini found that Campani’s smaller telescopes were more convenient to use, the optics of which were usually mounted in a long, lightweight wooden tube suspended on a high mast on the observatory terrace. In 1673 Cassini became a naturalized Frenchman, changing his name to Jean Dominic Cassini. In the same year, he married a French woman and she bore him a son, Jacques, who would succeed his father to become the next director of the Paris Observatory. In 1675, Cassini was observing Saturn under good seeing conditions when he discovered that its rings had a gap in them. On some occasions he could even see the planet’s globe while looking through the gap, and at other times, background stars could be seen to wink on and off as they moved through the opening. This famous gap in the rings is known as Cassini’s Division, one of many subsequently found with larger and more powerful telescopes. In 1683, Cassini independently discovered the zodiacal light, and correctly assumed that it was, in effect, a cloud or ‘aura’ of small particles surrounding the Sun. After 1683, he participated in geographic measurements, led by Jean Picard, and in 1692 he published a more detailed Moon map than that presented by his predecessor, Johann Hevelius. Over the last decade of his life, Cassini’s eyesight slowly faded, and by 1711, he was completely blind. After a short illness, he died on September 14, 1712. Cassini founded a dynasty of astronomers that continued to distinguish themselves well into the 19th century. As we have seen his son Jacques (1677–1756) succeeded him as director of the Paris Observatory. And Cassini’s grandson, César François Cassini (1714–84), as well as his great-grandson, Jean Dominique Cassini (1748–1845), followed in his footsteps by becoming future directors of the same. The reach of the long focus non-achromatic telescope also extended across the channel into England. Indeed, at least three of Huygens’ object glasses found their way there, including the 123-foot focus glass of 7.5-inch aperture, together with the aerial apparatus supporting it. This lens was presented by Constantijn Huygens junior to the Royal Society in 1692. However, the earliest use of the long focus singlet refracting telescope in England actually dates back several decades before this. Indeed, an excerpt from Samuel Hartlib’s Ephemerides, dating from August 1655, gave mention to the efforts of the Reverend Dr. John Wilkins of Wadham College, Oxford, who, with the help of some scientific friends, built an 80-foot focal length aerial telescope to conduct lunar research. Another of Wilkin’s friends, the wealthy lawyer, Sir Paul Neile, commissioned the construction of a long focus refractor in the late 1650s. In addition, we now know that around the same time, the

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Fig. 4.12  Sir Robert Hooke (1635–1703), one of England’s preeminent scientific polymaths. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Robert_Hooke#/media/ File:13_Portrait_of_ Robert_Hooke.JPG)

brothers Paul and William Ball had erected a 38-foot focus refractor on their large estate in South Devon in order to study the bright planets. It was Dr. Wilkin’s student and protégé, Sir Robert Hooke (1635–1703), who would become one of the most prolific users of long focus refractors in England, particularly in the decade between 1660 and 1670. As curator of instruments of the early Royal Society, Hooke had access to a number of large telescopes, of 6- to 60-foot focus. The objective lenses for many of these telescopes were fashioned by fellow Englishmen, Richard Reeves and Christopher Cox. Through experience, Hooke found that the telescopes with the best defining power were necessarily confined to apertures of between 2 and 2.5 inches and, like Huygens, he stopped down lenses of larger aperture. Observing from the quadrangle of Gresham College, Oxford, Hooke carried out original observations of the Moon and planets. Using his favorite instrument of 36-foot focus, Hooke published drawings of the main belts of Jupiter. He also recorded a large spot on the planet, which many scholars have traditionally identified as the famous Great Red Spot, an enormous anti-cyclonic storm moving through Jupiter’s atmosphere. But in recent years, some historians have cast doubt on this, pointing out that the spot seen by Hooke was too large and situated in the wrong place to be a good match (Fig. 4.12). Hooke’s skill as an observer is manifest in his extraordinary drawing of a single lunar feature – the crater Hipparchus – reproduced in his famous work, Micrographia, in 1665. Indeed, the detail he recorded using this primitive telescope is all the more

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Fig. 4.13  Drawings of the Moon and the Pleiades from Hooke’s Micrographia. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Robert_Hooke#/media/File:Moon_Micrographia_ Hooke.png)

remarkable in that it still stands up to modern images captured by telescopes of much superior quality to anything Hooke employed. He also observed a number of comets, detailed in his published work, Cometa (1678) with his long focal length refractors, particularly those of 1664 and 1677, identifying the key morphological features, such as the nucleus, coma and tail, terminology that astronomers still employ today (Fig. 4.13).

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Hooke noted that comet tails always pointed away from the Sun and thus necessitated some kind of force to propel them backwards. But what was the nature of such a force? Hooke took his questions to the laboratory, noticing how comet tail-­ like streams of bubbles were given off when an iron-coated wax ball was suspended in a long upright cylinder of acid. He deduced from this that the Sun’s force must have a corrosive effect on the head of the comet. And yet the same force did not seem to affect Earth! Incorrect as these ideas may have been; this kind of applied science was unheard of prior to the 1660s and 1670s and would set the scene for experimental space science after that. Hooke also pondered on the battered lunar surface with its myriad craters, asking himself what forces might have created them. Why had they formed on the Moon and not Earth? He decided to experiment by dropping a series of lead pistol balls from a height onto a tub of viscous, white clay. He found he could reproduce many of the morphological features of the lunar craters he had observed through his telescope, lending strong support for the impact theory of crater formation. Still others had claimed that the craters were caused by vulcanism, so Hooke set up experiments to blow air into a clay pipe and found that the bursting bubbles could indeed reproduce some features of craters, such as their steep walls, but not all. Both these theories were entertained for centuries, and although it is now acknowledged that impacts created the majority of lunar craters, vulcanism can best explain the origin of a few. Like Huygens and Descartes, Hooke was confident that as more powerful telescopes were brought to the fore, they would eventually allow mankind to see living creatures going about their business on the lunar surface. In this capacity, he envisaged the construction of a telescope of 1,000- or 10,000-foot focal length with a lens of 21 inches aperture! Many astronomers remained skeptical, however. Indeed, Adrien Azout, whom we briefly discussed in relation to the work of Huygens, wrote to the Royal Society claiming that Hooke’s fanciful telescope was just a pipe dream! After Hooke’s passing, the English astronomer James Pound resurrected the longest glass used by the Huygens brothers – of 123 feet focus – and mounted it at Wanstead Park on top of a maypole that had just been removed from Wanstead Strand. Many astronomers living in the vicinity paid Pound a visit to assess the quality of the views it served up. A one J. Crosswaite, assistant to the astronomer, John Flamsteed, looked at Jupiter through the optical monstrosity, declaring that he was not overly impressed with its performance; [It] showed me Jupiter, which I could perceive very distinctly, so that I believe the glass is good; but then the motion of the air, the shaking of the pole, etc., renders it very difficult to trace the object, and makes me conclude that not many good observations could be made with a glass of 123 feet long in the open air.

It was clear that the great aerial telescopes of the latter half of the 17th century had reached their limits. Their problems lay with the images formed by a single convex objective lens, which always produced a rainbow of colors around bright objects, robbing the image of much needed contrast (‘defining power’). Huygens, as we have seen, had attempted to reduce this effect by smoking his ocular lenses to

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Fig. 4.14  James Bradley (1693–1762), the astronomer who discovered the aberration of star light. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ James_Bradley#/media/ File:James_Bradley_by_ Thomas_Hudson.jpg)

block some of the unfocused light, but with limited results. Others, such as Sir Robert Hooke, conceived of ways of folding the light path using flat mirrors, but never brought his designs to working fruition. Necessity is the mother of invention, however, and it became increasingly clear that the telescope had to evolve in a different way to anything that had come before. Although falling into swift decline in the 1700s, the giant aerial telescopes of old were still being used by some astronomers well into the 18th century. On December 27, 1722, for example, Dr. James Bradley measured the diameter of Venus with an aerial telescope, the objective lens of which had a focal length of 212 feet, and in Italy, Francesco Bianchini tried to map the surface of that same planet and deduced its rotational period (unsuccessfully) in Rome in 1726–27 using a 2.6-inch aperture, 100-foot focal length aerial telescope. Perhaps the most astounding discovery attributed to the non-achromatic refractor is the aberration of starlight owing to Earth’s motion through space. It was discovered through the efforts of the English astronomer, James Bradley (1693–1762). As a protégé of both Sir Isaac Newton and Sir Edmond Halley, Bradley was well versed in the key scientific arguments of his day. By the 1720s, a huge body of indirect evidence amassed in support of the Copernican system, which included various planetary observations, geometry, probability and even some laboratory experiments, but still nothing that could provide clinching evidence that Earth moves through space. But a year after Sir Isaac Newton’s death, advances in technology and meticulous mathematical analysis finally provided that crucial evidence (Fig. 4.14).

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Measuring stellar parallax, that is, tiny angular changes in the position of the star, Gamma Draconis (which passed directly overhead at a pre-calculated time each day), as seen from opposite sides of its ‘presumed’ orbit about the Sun, wouldn’t be an easy task. Bradley had his friend and instrument maker, George Graham, construct a vertical telescope of 25-foot focus, set up at the home of his friend, Samuel Molyneux at Kew, London, so that when observers lay on their backs immediately under the eyepiece, they would see Gamma Draconis slowly drifting into the field of view at the allotted time. Then, with a highly accurate micrometer, Bradley would measure the star’s precise position with reference to the zenith point. Beginning in December 1725, Bradley began to make measurements every clear night. After just a few nights of observation, Bradley noticed that the star was culminating a little bit more to the south every 24  h. By March 1726, observations showed the star had ceased moving south and began to move back northwards, reaching its original (December) position again by June, after which it was observed to move northwards again until September 1726. It would then be seen to move southwards again to its December position. In other words, the star was shown to move in a tiny ellipse some 40 arc seconds wide against the sky. Using an improved vertical telescope (also designed by Graham) with a shorter focal length of 12.5 feet and possessing a wider field of view, set up at his uncle’s (the Reverend Dr. James Pound) rectory in Wanstead, Essex, the new telescope offered Bradley the chance to observe more stars in the field. Beginning in August 1727, this new telescope showed Bradley that all the stars exhibited the same behavior, that is, tracing out tiny ellipses on the sky with the same 40 arc second deviance. But what could be causing this effect? Most certainly, this could not be stellar parallax, as one would expect a larger parallax for nearby stars and a smaller value for stars situated farther away. It is claimed that the answer to this puzzling stellar motion came to Bradley as he sojourned 6 miles by boat down the River Thames from London to the residence of Dr. Halley at Greenwich, during which time the boat twisted and turned around many bends. Bradley had the presence of mind to note that a flag on board the boat always pointed in the same direction throughout the journey. This experience apparently gave him the inspirational solution to the conundrum. Let’s assume that the constant wind direction can be modeled as a constant stream of light emanating from the star Gamma Draconis. If we are orbiting the Sun, then for 6 months of the year – from March to September – we are moving into this stream of light. From September through to the following March, we would move in the opposite direction, that is, away from the stream of light. This would cause Gamma Draconis to be slightly displaced relative to the frame of reference of a terrestrial observer, depending on whether we move into or away from the stream of light (Fig. 4.15). A more detailed analysis of the apparent motion of the stars showed that as well as a shifting due to the aberration of starlight, there appeared to be a periodic shifting due to something else as well. Bradley suspected that this was due to the gravitational pull of the Moon upon Earth, causing our planet to wobble on its axis, in a phenomenon we now call nutation. To confirm this required a series of observations conducted over one complete revolution of the Moon’s nodes, and this entailed

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Fig. 4.15  The apparent position of a star viewed from Earth depends on Earth’s velocity. The effect is typically much smaller than illustrated. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Aberration_of_light#/ media/File:Simple_stellar_ aberration_diagram.svg)

nearly 19 years’ worth of further observations! Bradley’s announcement of his discovery was finally published by the Royal Society in 1748. Following their discovery, both aberration and nutation were corrected for in the reductions of the Greenwich Observations. The phenomena associated with Gamma Draconis were later described by Sir George Biddell Airy as the ‘birth-star of modern astronomy.’ Bradley’s discovery of the aberration of starlight proved fatal for those who still held out for a stationary Earth. Over the next century, even more compelling evidence for Earth’s motion was discovered, when the first stellar parallaxes were measured (discussed later in the book). The old ideas remained the same, but it was improving technology that provided the evidence to finally push the geocentric model of the universe over the edge. So, just how good were these non-achromatic refractors of old? We know of one reference dating from 1871 when a 10-foot (3.0-m) telescope by Campani was tested and was found to provide good definition and a flat field, with a magnification of about 20 times. In recent years, there have been some valiant attempts made by curious individuals to assess the efficacy of these early telescopes. In this capacity, amateur astronomer and planetary scientist Dr. Alan Binder, based at the Lunar Research Institute in Tucson, Arizona, made a systematic investigation of double stars brighter than magnitude 5.5 using an entirely homemade instrument – including the object glass and eyepieces! Calling it the Hevelius, Binder’s telescope consisted of an uncoated, plano-convex objective of 17-foot focus, having a clear aperture of just 2.8 inches. The object glass was placed inside a long wooden tube

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Fig. 4.16  The Hevelius, a modern non-achromatic telescope with a 17-foot focus. (Image courtesy of Alan Binder. Used with permission)

that was itself mounted on a pole. Three Huygenian eyepieces were employed, yielding powers of 50×, 100× and 150× (Fig. 4.16). Binder investigated its performance on a number of double star targets, acknowledging that only two such systems were discovered during this era using these telescopes – Mizar, discovered by Benedetto Castelli (a former student of Galileo) in 1617 and re-discovered by Riccioli in 1643, and γ Arietis, discovered by Hooke in 1664. Binder showed that about 175 double stars down to magnitude 5.5 could be resolved with this typical 17th century telescope and that it resolved pairs as close as 2.3 inches, just 50 percent poorer than the Dawes limit (the traditional resolution limit for equally bright components used by double star observers)! Why then the discrepancy between the tally of double stars discovered by astronomers from the 17th century and Binder’s very encouraging results? One explanation is mechanical convenience (Fig. 4.17). The Hevelius was small enough and mounted well enough to allow Binder to accurately point it at many stars in the sky, while those constructed by historical astronomers were often longer and more unwieldy than Binder’s experimental setup. In their zeal to make their telescopes bigger and better, these astronomers of old made their telescopes too cumbersome to use systematically! (Fig. 4.18) Either way, Dr. Binder’s independent research indicated that a considerable amount of useful work could be done with a modest non-achromatic telescope and

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Fig. 4.17 Showing Binder’s micrometer used to measure a suiet of double stars with the Hevelius. (Image courtesy of Alan Binder. Used with permission)

Fig. 4.18  The 2.8-inch singlet object glass and Huygenian oculars. (Image courtesy of Alan Binder. Used with permission)

that the images were not as bad as is commonly expressed in the literature. Still another possibility is that the astronomers of the day were not overly concerned with double stars, being more preoccupied with Solar System objects, and so were less likely to seek them out, unlike in later centuries, when double star astrometry formed the lion’s share of astronomical investigation (Fig. 4.19). It is clear that though the non-achromatic refractor was far from perfection in the modern sense of the word, it was nonetheless used to great effect by a number of astronomers to substantially increase our knowledge of the cosmos (Fig. 4.20). Through their painstaking observations and the genius of the trained human eye, they extended the frontiers of knowledge and inspired new generations of sky gazers to take up the gauntlet. By the latter part of the 17th century, the stage was set

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Fig. 4.19  Drawings of Jupiter made with the Hevelius. (Image courtesy of Alan Binder. Used with permission)

for an entirely new kind of telescope that would transcend the traditional limits of the long focus non-achromatic, and it would be achieved not by refraction through a lens but by reflection. In the next chapter, we shall explore the work of these early pioneers and the extraordinary results they achieved (Fig. 4.21).

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Fig. 4.20  Drawings of Mars made using the Hevelius. (Image courtesy of Alan Binder. Used with permission)

Fig. 4.21  Sketch of the Orion Nebula made with the Hevelius. (Image courtesy of Alan Binder. Used with permission)

Sources

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Sources Chapman, A.: Stargazers; Copernicus, Galileo and the Telescope. Lion Hudson, Oxford (2014) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) King, H.C.: The History of the Telescope. Dover, New York (1955) Manly, R.: Unusual Telescopes. Cambridge University Press, Cambridge (1991) Price, F.W.: The Planet Observer’s Handbook. Cambridge University Press, Cambridge (2000) Sagan, C.: Cosmos. Macdonald Futura Publishers, London (1980) Simpson, P.: Guidebook to the Constellations. Springer, New York (2012) Watson, F.: Stargazer: The Life and Times of the Telescope. Da Capo Press, Cambridge, MA (2004) Christian Huygens and His Telescopes. http://www.esa.int/esapub/sp/sp1278/sp1278p1.pdf Double Star Observations with a 17th century Achromatic Telescope. http://www.jdso.org/volume6/number4/binder47.pdf

Chapter 5

Workers of Speculum

In the last chapter, we explored the rise of the long focal length, non-achromatic refractors, containing a singlet objective lens and how, though unwieldy and difficult to use, skilled observers were able to use them to push back the frontiers of knowledge, showing humankind that the universe was vastly more complicated and interesting than anyone had dared imagine before. But even in these early days of telescopic astronomy, there were many who already felt that there must be better ways to bring the universe closer, more convenient contrivances to explore the heavens. This quest led some to consider the properties of mirrors rather than lenses. The ability of mirrors to focus light has been known since antiquity. In his Natural History, the 1st century Roman aristocrat and naturalist, Pliny the Elder (23–79 a. d.), hearkening back to the hallowed age of the Roman republic, gave mention to their destructive power when used in warfare: “It surpasses all wonder that a day goes by wherein the whole world is not consumed in flame. For concave mirrors turned toward the Sun ignite more easily by its rays than does any other fire.” Pliny was probably referring to the wonders produced by the Greek scientist and mathematician Archimedes of Syracuse (b. c. c.287–212), who fashioned a large bronze concave mirror to set ships from the invading Roman fleet ablaze during the siege of the Greek city of Syracuse between b. c. 215 and 212. Less sensational but more edifying from the point of view of the history of scientific progression are the works of Diocles who, in the 3rd century b. c., studied the physics of burning mirrors, as well as later studies on reflection by concave mirrors conducted by Anthemius in the 6th century a. d. Although many more works have been lost in the mists of time, the power of the mirror to produce images was never far from the minds of innovators. Indeed, it was only a few years after Galileo entered onto the world’s stage with his homemade refracting telescopes that some of his admirers took up the gauntlet to make telescopes using mirrors, including a number of mathematicians of repute, such as Rene Descartes, Bonaventura Francesco Cavalieri and Marin Mersenne. Invariably, though, their work was more theoretical than practical, and none of them put their designs into practice.

© Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_5

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The earliest known reference to a reflecting telescope comes from the Italian Jesuit priest Niccolò Zucchi (1586–1670), who is reputed to have fashioned a telescope using a concave mirror instead of a lens as early as 1616. The fourth child in a family of eight siblings, Zucchi studied rhetoric in Piacenza and philosophy and theology in Parma. After the completion of his studies at the age of 16, Zucchi entered the Jesuit order in Padua on October 28, 1602, remaining there for much of his life. Zucchi taught mathematics, rhetoric and theology as a professor at the Collegio Romano and then was appointed as rector by Cardinal Alessandro Orsini, In 1623, Zucchi was sent as a papal legate to the court of Ferdinand II, duke of Tuscany. There he met the famous German astronomer and mathematician Johannes Kepler, who encouraged Zucchi’s interest in astronomy and optics and maintained correspondence with him after returning to Rome. At one point when Kepler was in financial difficulties, Zucchi, at the urging of the Jesuit scientist Father Paul Guldin, gifted a telescope of his own design to Kepler, who mentioned it in his book Somnium (1608). Zucchi, together with fellow Jesuit, Daniello Bartoli, were among the earliest observers to see the belts on the planet Jupiter on May 17, 1630, and he also reported spots on Mars in 1640. For his contributions to astronomical knowledge, the lunar crater Zucchius was named in his honor (Fig. 5.1). Zucchi described his reflecting telescope in his work, Optica philosophia experimentis et ratione a fundamentis constituta, published sometime in the early 1650s. And while he did claim to have used such an instrument to view objects, both “celestial and terrestrial,” he must not have been overly impressed with his own

Fig. 5.1  Niccolò Zucchi (Dec. 6, 1586 to May 21, 1670), an Italian Jesuit, astronomer and physicist. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Niccol%C3%B2_ Zucchi.png)

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efforts, for we learn that he went right back to building and using long focal length singlet refractors. It was the Scottish mathematician and astronomer, James Gregory (1638–75), who first proposed a viable reflecting telescope in a work entitled Optica Promota, dating from 1663. In this work, Gregory made mention of the unique properties of a parabolic mirror in eliminating an optical defect known as spherical aberration. Gregory pointed out that a reflecting telescope with a parabolic mirror would correct spherical aberration as well as the chromatic aberration (since a mirror can reflect all wavelengths of visible light equally well) seen in refracting telescopes. In this ground-breaking design, he suggested placing an elliptical secondary mirror surface past the focal point of a parabolic primary mirror, reflecting the image back through a hole in the primary mirror, where it could be conveniently viewed (Fig. 5.2). By his own admission, though, Gregory had no practical skill and could not enlist a local optician capable of actually constructing a working instrument. He decided instead to go to London in 1664 to discuss the design of the new reflecting telescope with England’s best opticians. Gregory ordered up a 6 foot focus mirror from Richard Reeves and John Cox, but their efforts proved shoddy, to put it mildly. Disillusioned, Gregory took himself off to Italy, spending the next 4 years in Padua, where he had linked up with his compatriot, John Caddenhead, who was a professor of philosophy at the local university. Here he stayed and studied for 4  years (Fig. 5.3).

Fig. 5.2  James Gregory (1638–1675). (Image courtesy of Wiki Commons. https://en.wikipedia. org/wiki/James_Gregory_%28mathematician%29#/media/File:James_Gregory.jpeg)

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Fig. 5.3  Design of a Gregorian reflecting telescope. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/File:Gregorian_telescope.svg)

Meanwhile, back in England, another young man set his sights on devising a reflecting telescope, and his ruminations on optics were to change the world utterly and forever. His name was Isaac Newton (1642–1727). Having thrown himself into optical experiments, Newton came to the conclusion that it was not possible for white light to be refracted without undergoing dispersion (producing a rainbow of colors). Although this proved to be an erroneous conclusion, it impelled him to create his own rendition of the reflecting telescope in 1668. The Gregorian design was very elegant, but it was much more difficult to create in comparison to the sheer simplicity of Newton’s solution. Intimately acquainted with ‘chimistry,’ he first cast a special alloy, which he called bell metal, consisting of about six parts copper and two parts tin. To this mixture, Newton also included one part of arsenic, believing it to give the metal a whiter reflection. Add more copper and the image would be yellowed, mix in too much tin, and the cast would be overly blue (Fig. 5.4). Newton’s chosen combination was found to give good reflectivity in a natural color. The mirror blank was a cylinder 2 inches in diameter and a third of an inch thick. Newton recounts some details of the design of the telescope in his Opticks (1704) (Fig. 5.5): The diameter of the sphere to which the Metal was ground concave was about 25 English Inches, and by consequence the length of the Instrument about six Inches and a quarter. The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times. By another way of measuring I found it magnified 35 times. The concave Metal bore an Aperture of an Inch and a third part, but the Aperture was limited not by an opake Circle, covering the limb of the Metal round about, but by an opake Circle, placed between the Eyeglass and the Eye, and perforated in the middle with a little round hole for the Rays to pass through to the Eye. For this Circle being placed here, stopp’d much of the erroneous Light, which otherwise would have disturbed the Vision. By comparing it with a pretty good Perspective of four Feet in length, made with a concave Eye-glass, I could read at a greater distance with my own Instrument than with the Glass. Yet Objects appeared much darker in it than in the Glass, and that was partly because more Light was lost by Reflexion in the Metal, than by Refraction in the Glass, and partly because my Instrument was overcharged. Had it magnified but 30 or 25 times, it would have made the Object appear more brisk and pleasant.

Newton found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus with his new little telescope. To Newton, the construction of this telescope was child’s play, a mere curious aside. But what a toy

5  Workers of Speculum Fig. 5.4  Sir Isaac Newton (1642–1727). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Isaac_Newton#/media/ File:Bolton-newton.jpg)

Fig. 5.5  The dispersive properties of a glass prism, which produces the familiar rainbow of colors when white light passes through it. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ Isaac_Newton#/media/ File:Dispersive_Prism_ Illustration.jpg)

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Fig. 5.6  A replica of Newton’s second reflecting telescope. (Image courtesy of Andrew Dunn. Used with permission)

nonetheless! In the autumn of 1671, Newton constructed a second ‘speculum’ telescope, which wound up at a meeting of the Royal Society on January 11, 1672, where it is safe to say that it caused a sensation. Among the distinguished guests were King Charles II and Sirs Robert Hooke and Christopher Wren, who pronounced it an optical marvel. Small wonder that Newton got elected to the Royal Society the very same evening! To the great lens makers of the day, news of Newton’s reflecting telescope must have caused fear and wonder in equal measure. On the one hand, the intimidating size of the instrument – just half a foot long – that could be picked up and used at a moment’s notice, yielding well defined images free of chromatic aberration, was worlds’ apart from the unwieldiness of the long lens. On the other hand, Newton demonstrated the power of a reflective surface, a property that would presage a future era when astronomers would build truly monstrous reflecting telescopes greatly exceeding anything built with a lens (Fig. 5.6). However, as good as Newton’s telescopes were, they were not without their faults. For instance, in learning more about the mirror polishing techniques employed by Newton, reconstructive historians have concluded that it would have imparted a so-called turned edge to it. This occurs when the curvature of the peripheral parts of the mirror is slightly less than at the center. In addition to this, because Newton didn’t bother to parabolize his mirror, keeping instead the simpler, spherical shape, the telescope exhibited some spherical aberration – an optical defect arising from rays being focused at different loci from the edges and central parts of the mirror. Newton partially remedied this by inserting a small hole between the eyepiece and the eye, effectively blocking off rays derived from the edge of the mirror. Later in 1672, shortly after the sensationalism surrounding Newton’s telescope reached the ears of astronomers across Europe, news came that a French Catholic

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Fig. 5.7  Schematic of the Cassegrain telescope. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/Cassegrain_reflector#/media/File:Cassegrain_Telescope.svg)

priest, Laurent Cassegrain (1629–93) had invented an altogether different type of reflecting telescope. Although his early life is still shrouded in mystery, we do know that Cassegrain was ordained into the priesthood and became a high school teacher in the town of Chartres, France. We also know that there were a few Cassegrains living in the same town, including a one Siuer Guillaume Cassegrain, who happened to be a skilled metal worker. Cassegrain’s association with the telescope is still the subject of controversy, however, with some historians claiming that he had made the instrument several weeks before Newton’s reflector was presented to the Royal Society. Cassegrain’s design first appeared in the eighth edition of the 17th century French science journal Recueil des mémoires et conférences concernant les arts et les sciences, published by Jean-Baptiste Denys in April 25, 1672, but is unclear when or if the instrument was completed. What is certain, however, is that the Cassegrain reflector differed significantly from that devised by Newton, where a curved secondary mirror was suspended above a primary concave mirror. On June 13, 1672, Christiaan Huygens wrote about the Cassegrain design, critiquing it harshly, perhaps out of loyalty to his revered English friend or because he felt Newton’s design was being sabotaged by this alternative. Cassegrain’s design actually held several distinct advantages over both Newton’s and Gregory’s designs, but alas these advantages were completely overlooked at the time. Indeed, a much later analysis performed by the English telescope maker Jesse Ramsden showed that the combination of a concave primary and convex secondary tended to cancel out the aberrations of each component, as opposed to being additive in the case of Gregory’s design. In addition, the Cassegrain optics could accommodate a shorter, and therefore more conveniently sized tube than that proposed by the Gregorian counterpart (Fig. 5.7). Newton himself waded into the debate on the relative merits of his own design and the newly arrived Cassegrain, clearly finding fault with the latter: The advantages of this design are none, but the disadvantages so great and unavoidable, that I fear it will never be put into practice with good effect…..I could wish, therefore, Mr. Cassegrain had tried his design before he divulged it. But if, for further satisfaction, he please hereafter to try it, I believe the success will inform him, that such projects are of little moment till they be put in practice.

In what can only be viewed as a case of flagrant prejudice, the Royal Society dispatched a description of Newton’s telescope to Christaan Huygens, who in turn,

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used his clout with the French Academy to endorse its superiority over the Cassegrain design. Huygens sycophantically stated that in the case of Newton’s telescope, far less light was lost by reflection than refraction, a statement shown to be patently false upon later historical inspection by reconstructive historians. Indeed, compared with later alloys, the reflectivity of Newton’s mirrors were quite poor; bringing to focus just 16 percent of the gathered light! Whatever the motives, the storm of controversy that attended the work of Father Cassegrain had one lasting effect: his name was all but forgotten for a very long time. But it wasn’t really the reflectivity of Newton’s mirrors that was holding back their general introduction to the astronomical community so much as the difficulty of figuring them to the required shape for them to work well; that took another three decades! The game-changing instrument came from the mind and hands of the English telescope maker John Hadley (1682–1744). Born in London, the second son of six children of well-to-do estate owners, George and Katherine Hadley, little is known about his early years and education, save for the inference that he must have received a sound schooling in mechanics, for at the age of 35, he was made a Fellow of the Royal Society on March 21, 1717, where he was apparently held in high esteem. Indeed, he went on to serve as its vice president in 1728. Starting around 1719, Hadley tried his hand at figuring speculum mirrors and, with the assistance of his brothers George and Henry, succeeded in fashioning a 6-inch primary mirror with a focus of 62 inches (with a f/10 focal ratio). Moreover, the shape of the primary mirror was that of a parabola, which can bring all rays of light incident upon the mirror surface to the same focus, thereby greatly improving the defining power of the images it served up by reducing spherical aberration (Fig. 5.8). Fig. 5.8  John Hadley (1682–1744). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ John_Hadley#/media/ File:John_Hadley.jpg)

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The instrument made its first public appearance at a meeting of the Royal Society that convened on January 12, 1721. The records from this meeting state: Mr. Hadley was pleased to show the society his reflecting telescope, made according to our President’s [Newton] directions in his Optics, but curiously executed by his own hand, the force of which was such, as to enlarge an object near two hundred times, though the length thereof scarce exceeds six feet, and, having shewn it, he made a present thereof to the Society, who ordered their hearty thanks to be recorded for so valuable a gift.

Hadley’s instrument understandably attracted a lot of attention, and it was soon put to the test against the best telescopes in England at that time. Accordingly, the instrument was brought to Wanstead Park, where it was set up against Huygens’ 123-foot focus refractor by Dr. James Bradley and James Pound, and comparisons were made ‘on the bodies and satellites of the superior planets.’ The definition of both instruments was found to be about the same, with the brighter image going to the refractor. This was understandable, given that the Huygenian lens had a larger aperture (7.5 inches), but it was the ease with which the instrument could be moved from object to object that most impressed all those gathered. Hadley had also submitted an account of his own observations he made with his 6-inch Newtonian on the satellites of Jupiter and Saturn, in the company of two other gentleman: “Mr. Folkes and Dr. Jurin being present…he had seen the shadows of first and third satellites on the body of Jupiter, and, in May, 1722, the dark Line in the Ring of Saturn.” (Fig. 5.9) Hadley did not leave any details on how he constructed his reflecting telescope but was gracious to others who wished to make their own instruments. Dr. James Bradley, now a professor of astronomy at Oxford University, together with Samuel Molyneux, instructed two London opticians, Scarlett and Hearne, to cast and figure new specula, but their results were not encouraging, finding it exceedingly difficult to polish. These failures impelled Molyneux to experiment with a wide range of speculum mirrors – 150 varieties in all, with differing amounts of copper, tin and arsenic. First, the copper (which has a much greater melting point than tin) was melted, and then the other constituents were added – ingots of tin and a pinch of arsenic. The melt was then poured into an iron mold lined with clay or sand, so that it took on the rough curvature of the desired mirror. Once cast, the mirror was ground more finely with either sand or emery, the curvature controlled by varying the stroke. Hadley had found that circular strokes increased the curvature, while horizontal strokes tended to decrease it. The mirror then had to be polished, but in many ways this was the most challenging part, for the very act of imparting a brilliant and even sheen to the speculum metal caused its curvature to change. To make the polishing tool, a brass tool first had to be constructed. The tool was turned on a lathe and roughly ground into a concave form by shaping it on a marble slab of opposite (convex) curvature. Next, a convex glass disk was ground using emery. Finally, the convex glass was covered with pitch-impregnated silk, which formed the polishing tool proper. Hadley had also learned to convert a spherical mirror into the shape of a parabola by deepening the curvature by a tiny amount at its center. This, he discovered, could be done by imparting a spiral stroke to the mirror for about 30 seconds. As one can

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Fig. 5.9  Hadley’s reflecting telescope with a parabolic mirror. (Image courtesy of the Royal Astronomical Society)

imagine, this work was painstaking, and at every stage its curvature had to be tested. Accordingly, Hadley had devised rather sophisticated ‘bench’ tests that served as the forerunner of even better methods introduced by Leon Foucault 160 years later. Placing an illuminated pinhole at the center of curvature of the mirror, he used an eyepiece to inspect the reflected cone of light. Indeed, we have an account of such testing in Robert Smith’s 1738 work, A Compleat System of Opticks: If the area of the light, just as it comes to or parts from the point, appears not round but oval, squarish or triangular etc., it is a sign that the sections of the specular surface, through several diameters of it, have not the same curvature. If the light, just before it comes to a point, have a brighter circle round the circumference, and a greater darkness near the centre, than after it is crossed and is parting again; the surface is more curved towards its circumference and flatter about its centre, like that of a prolate spheroid round the extremities of its axis; and the ill effects of this figure will be more sensible when it comes to be used in the telescope. But if the light appears more hazy and undefined near the edges, and brighter in the middle before its meeting than afterwards, the metal is then more curved at its centre and less towards the circumference; and if be in a proper degree, may probably come near the true parabolick figure. But the skill to judge well of this, must be acquired by observation.

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Although a parabolic surface was recognized as the ideal figure for a Newtonian primary mirror, it was not strictly necessary, as long as the focal length be kept adequately long. More precisely, the mirror could be made perfectly spherical if its focal length be equal to or greater than 4.46 × (aperture)^4/3. So, for Hadley’s 6-inch mirror its focal length need only have been 4.46 × (6)^4/3, that is, 48.6 inches, to perform well while utilizing a spherical curve. Since the real focal length of Hadley’s primary mirror was 62 inches, it exceeded this minimum by 13 inches. Hadley also constructed a variety of Cassegrain and Gregorian reflectors, devising new methods and guidelines for their fabrication. Having good working models to study, it wasn’t long before other opticians took up the gauntlet to craft their own renditions of the reflecting telescope, some good, but many not so good. That said, they were all eclipsed by the extraordinary efforts of a Scotsman, who greatly advanced the cause of the reflecting telescope and elevated it to the status of an art form. His name was James Short (1710–1768). Born in Edinburgh in 1710, Short received a good education, progressing to Edinburgh University in 1726. There, he attended lectures by Colin Maclaurin, Professor of Mathematics, and became intensely interested in the science of optics. MacLaurin was a friend of James Douglas, Lord Aberdour, later Earl of Morton, an Edinburgh natural philosopher who had himself become a Fellow of the Royal Society (Fig. 5.10). Douglas also became an early patron of Short’s, appointing him tutor his children. Short accompanied Morton to the island of Orkney, off the northeastern coast of Scotland in 1739, surveying Morton’s lands, but also working on refining the length of a degree of latitude. Impressed by his knowledge of optics, Maclaurin encouraged Short to experiment on various telescopic designs, offering him a room at Edinburgh University to carry on his researches. And set to work he did, first trying his hand at figuring glass surfaces before backing them with quicksilver (Mercury). But Short soon found that the glass had too many veins, and obtaining a truly uniform mercury film proved almost impossible. He thus returned to casting and figuring speculum metal mirrors, and their quality was rumored to be superior to anything that had been produced hitherto. Short worked mostly on Gregorians and, when MacLaurin wrote to Robert Smith in 1734 of his success, Smith published the account of Short’s progress in his Opticks. Short could hardly have had a more propitious introduction to the world of practical optics. He became a Fellow of the Royal Society on a visit to England in 1737 and established a successful business by the time he moved his operations permanently to London in 1738, though he would always maintain his links with his homeland and Edinburgh, which he continued to visit regularly. Maclaurin personally tested a few of Short’s telescopes and had this to say about them: I have compared some of these with such as have been brought from London; and find one of Mr. Short’s of six inches focal distance, compared with one of the best I have seen from London of nine inches and three tenths focal distance, to exceed it in brightness, distinctness and magnifying power; and when I called an indifferent person, who knew not who made the instruments, to give his opinion, he very readily preferr’d that of six inches focal distance. It also manifestly exceeded another I had from London of eleven inches and a half focal distance. The same was the result of some other comparisons.

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Fig. 5.10  A schematic drawing of James Short’s tabletop reflector. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/James_Short_%28mathematician%29#/media/File: Equatorial_telescope.png)

Short operated a private observatory at his business premises in Surrey Street, Strand. His commercial interests, as other important makers would find, did not prevent him from reaching a respected position in the London scientific world, serving on the Council of the Royal Society. The Newtonian basis of his craft was helpful in cultivating his position and he adopted the moniker of ‘optician solely for reflecting telescopes’. One of Short’s telescopes was purchased by Queen Caroline of Ansbach, wife to the then British monarch, George II, who also invited Short to tutor her youngest son, Prince William, Duke of Cumberland (Fig. 5.11). Short constructed over 1,360 telescopes in his lifetime, not only for customers in Britain but also for export. One such instrument is still preserved in Leningrad, Russia, another in Uppsala, Sweden, and several others found their way across the Atlantic to the American colonies. The majority of Short’s telescopes were small, ornate Gregorian reflectors of 2–6 inches of aperture, which were equally applied to

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Fig. 5.11  One of Short’s tabletop Cassegrain reflectors on display at Bamburgh Castle, England. (Image by the author)

terrestrial as well as astronomical observing. The tubes were constructed from high quality brass and mounted on elegant altazimuth mounts, which much endeared them to future preservation by collectors and antiquarians. But he had also made some monsters, including 18-inch instruments of 12  feet effective focal length, which were purchased (at great expense) by aristocratic dilettantes (in this case, the King of Spain) who, it must be admitted, never used them to make any astronomical discoveries. In this capacity, they were more works of art than scientific instruments. There are also records of a few Newtonian reflectors made by Short, the largest of which was 9.5 inches in aperture, delivered to the Royal Observatory in Greenwich, London (Fig. 5.12). Accompanying each telescope, Short supplied an erect image ocular, together with several higher power eyepieces for astronomical viewing. Short cunningly perceived that the majority of his customers came to conflate the quality of the telescope with the level of magnification it could withstand, and, a result, he often overstated the true magnifying power of his eyepieces in order to maximize sales. This was an unfortunate advertising strategy, as other opticians followed suit, thus cultivating the notion that instruments offering high magnifications were n­ ecessarily superior to those offering lower powers. For example, Short offered two instruments, both of 3-inch aperture and a focal length of 1 foot. The first instrument had a high magnification eyepiece of 85 diameters and the second, 110 diameters, with prices of 10 and 14 guineas, respectively.

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Fig. 5.12  Another view of one of Short’s 18th century telescopes. Note the single stalked secondary pickoff mirror. (Image by the author)

Worse still, the magnifications of many of his eyepieces were greatly overstated, a fact that was overlooked by the majority of his customers but subsequently uncovered by more inquisitive astronomers. William Herschel once had the opportunity of examining a variety of Short’s telescopes, from 2 to 12 feet focus, set up at Edinburgh Observatory, and recounted the following: I viewed several land objects thro’ them. The large one which has the reputation of being a very bad instrument appeared to me not to be very defective, but the presumption seems to be in favour of its being good. I could only see the top of a steeple, and even there a great part of the light was lost by being confined in the opening of the roof…. I saw again the large reflector at the observatory and measured its power, which was said to be 800; I found it 130, the aperture is 12 inches.

In retrospect, it appears as though Short was deliberately under powering his telescopes to suppress the optical defects he assumed they exhibited. An aperture of 12 inches, the optical surface having been properly formed to a diffraction limitation of c. 1/4 wavefront error, should allow a magnification of approximately 360× in steady atmospheric seeing (i.e., 30× times the aperture in inches). Clearly 130× is a veritable country mile away from 800× and significantly less than 360×! Like many instrument makers of his era, Short was reticent about the methods he employed in the production of his speculum telescopes, and indeed left no records for historians to examine. It was reported that, out of professional jealously of other makers, he had all his tools destroyed before his death, but is still doubtful whether

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any of his optical contemporaries would have been able to create anything quite as good as Short himself anyway. Short was also an accomplished telescopist, authoring numerous communications addressed to the Royal Society between 1736 and 1763. Several were related to his observations of aurorae, eclipses and occultations, but others were of greater historical interest. For example, near sunrise on the morning of October 23, 1740, Short viewed Venus and believed he uncovered a satellite of the planet showing an identical phase. This was likely to be a ghost image caused by a reflection in the uncoated Huygenian eyepieces he employed in his instruments. He also observed the transit of Mercury on 6 May 1753, as well as the transit of Venus on 6 June 1761 from Savile House, a residence of the Duke of York. By examining records of observations of the same phenomenon made in various parts of Europe, as well as at the Cape of Good Hope in South Africa, Short was able to deduce a solar parallax of 8″.65, very close to the modern value of 8.80″. Some of his instruments travelled on The Endeavour with Captain James Cook (1728–79) to observe the next transit of Venus due to occur on June 3 1769, but Short died a year before this event took place. With his passing, Short took with him the accumulated experience of 35  years of telescope manufacture. He also left behind a fortune amounting to £20,000, as well as 64 unmounted telescope mirrors, and a fully completed 12 foot Gregorian reflector, which were bequeathed in Short’s will to his brother, Thomas, who by this time had set up his own optics workshop in Leith, Scotland. Thomas arranged for the 12 foot Gregorian to be set up at Calton Hill, the site of Edinburgh Observatory, but it soon fell into disuse and was dismantled for scrap a few short years later. It was not long before other telescope makers came to fore to fill the vacuum created by Short’s passing, and one of the most successful was the English physician and amateur astronomer named John Mudge (1721–93). The fourth and youngest son of the Reverend Zachariah Mudge, by his first wife, Mary Fox, Mudge was born at Bideford, Devon, and educated at Bideford and Plympton grammar schools, before going on to study medicine at Plymouth Hospital. Mudge established himself as a well-to-do surgeon, and in his spare time he took up the hobby of casting and figuring speculum mirrors, a skill which he apparently excelled at, for in 1777 he was awarded the prestigious Copley Medal of the Royal Society. Mudge experimented with various alloys, including some composed of silver, brass and arsenic. He soon changed back to traditional metals, though, creating his unique speculum of copper and tin in the ratio 2.2 to 1, respectively (Fig. 5.13). Unlike Short, though, Mudge was willing to communicate his techniques to a wider audience, and in his 1777 publication in the Transactions of the Royal Society, he divulges something of his methodology: Four tools are all that are necessary; viz. the rough grinder to work off the rough face of the metal; a brass convex grinder, on which the metal is to receive its spherical figure; a bed of hones which is to perfect that figure and to give the metal a fine smooth face; and a concave tool or bruiser, with which both the brass grinder, and the hones are to be formed. A polisher may be considered as an additional tool; but as the brass grinder is used for this

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Fig. 5.13  John Mudge (1721–1793). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/John_ Mudge#/media/File:J. Mudge.jpg)

purpose, and its pithy surface is expeditiously, and without difficulty formed by the bruiser, the apparatus is therefore not enlarged.

Polishing the metal proved, as Short had no doubt found, to be the most challenging part of mirror production. Using a polishing lap similar to his predecessors, he used circular strokes, beginning at the center of the mirror and gradually moving outwards. More vigorous polishing at the center turned the spherical surface of the speculum into that of a paraboloid. Mudge used a different method of testing his newly completed mirrors, however; he employed a pair of diaphragms that occluded the center and then the edges of the mirror. This was followed up with high power tests conducted in daylight to compare and contrast the images. The closer they corresponded the better the figure. In so doing, Mudge’s tests formed the basis of more sophisticated ‘zonal analysis’ performed by modern opticians. Though he undoubtedly made many telescope mirrors, historians have only been able to trace two instruments to his hand: one for the Anglo-German diplomat and astronomer John Maurice, Count of Brühl, which eventually ended up at Gotha Observatory, Thuringia, Germany. The other was bequeathed to his son, the artillery officer and surveyor, William Mudge. In retrospect, the real significance of Mudge’s work is that, in communicating his methodologies to a wider audience, many more individuals could finally try their hand at casting, grinding and polishing good quality speculum metal mirrors. In 1787, the Reverend John Edwards of Ludlow, Shropshire, an inveterate tinkerer in mirror making, published a treatise on the composition and casting of spec-

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ula in the Nautical Almanac, in which he described experiments with various combinations of metal and other minor ingredients. He found that an alloy consisting of 32 parts copper, 15 parts tin, and one part each of brass, silver and arsenic, produced the hardest, whitest metal. Edwards became adept at constructing small Gregorian and Newtonian telescopes, and though there is little in the literature to testify to their quality, we do have one account by the distinguished astronomer, Nevil Maskelyne (1732–1811): Mr. Edwards telescopes shew a white object perfectly white, and all objects of their natural colours; very different from common reflecting telescopes which give a dingy copperish appearance to objects. I found, by careful experiment that they saw objects as bright as a treble object glass achromatic telescope, both being put under equal circumstances as areas of the aperture of the object metal and object glass, and equal magnifying powers; whereas the aperture of a common reflecting telescope must be that of an achromatic as 8 to 5, to produce an equal effect.

Thus, by the end of the 18th century reflecting telescopes were beginning to rival those of the refracting telescope. The figuring of speculum metal had advanced to such a degree that small reflecting telescopes of high quality could be routinely produced by the opticians of the day, but larger instruments of the same genre were still of questionable quality. Indeed, while many telescope makers tried their hand at constructing large instruments, some up to 29 inches in aperture, they invariably were better suited to ornamental display than advancing the cause of astronomical science. This is supported by the fact that little new was discovered using these instruments compared with what had been uncovered with the great aerial telescopes of old. And yet one man was to buck this trend, using a variety of modest instruments  – both reflectors and refractors  – to carve out an immortal name for himself among the stars – the French amateur astronomer Charles Messier (1730– 1816), whose legacy will be explored in the next chapter.

Sources Bell, L.: The Telescope. Dover, New York (1981) English, N.: Choosing and Using a Dobsonian Telescope. Springer, New York (2011) Hall, R.: Isaac Newton: Adventurer in Thought. Cambridge University Press, Cambridge (1999) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) King, H.C.: The History of the Telescope. Dover, New York (1955) Newton’s Reflecting Telescope as presented by Professor Martyn Poliakoff at the Royal Society, London. https://www.youtube.com/watch?v=4ESW_NTIhBM North, J.: The Fontana History of Astronomy and Cosmology. Fontana Press, London (1994) Pliny the Elder: Natural History: A Selection. Penguin Classics, New York (1991) A Gregorian Telescope. http://adsabs.harvard.edu/full/1958JRASC..52..255B

Chapter 6

Charles Messier, the Ferret of Comets

The year 1729 was an auspicious one for telescope optics. The English jurist and mathematician, Chester Moor Hall (1703–77), combined two different types of glass lenses to create the first achromatic doublet, thereby solving (or nearly so) a long-standing defect of refracting telescopes, chromatic aberration. We have learned in previous chapters that a single lens cannot bring all the rays present in white light to a single focus, owing to the differing refractive indices for different wavelengths of light as they pass through the glass. This led to dispersion, an effect that Newton himself thought impossible to ameliorate (Fig. 6.1). Inspired by an erroneous belief that the human eye produces images without chromatic aberration, Moor Hall wondered whether, just as the eye possesses a crystalline lens and vitreous humor, a compound lens could be constructed using two different transparent materials. Moor Hall had carried out experiments in his spare time with two kinds of glass of opposite powers: a convex lens (positive power) fashioned from crown glass and a concave lens (negative power) made from flint glass. The dispersion produced by the crown element was almost canceled out by introducing the flint element. Moor Hall had these lenses made by two different London opticians – Edward Scarlett of Soho and James Mann of Ludgate Street, but unbeknownst to him, they subcontracted the work to the same optician, George Bass, who noted that each lens was of the same diameter, namely 2.5 inches. Bass didn’t take long to put two and two together and decided to combine the lenses to produce the world’s first achromatic doublet with a focal length of 20 inches. This objective exhibited much superior chromatic correction to the singlet convex lenses used in the great aerial telescopes of the 17th century. Moor Hall was far too unassuming a man to press the idea any further than a few acquaintances, who evidently didn’t think all that much of the invention, but as news of the new doublet lens trickled out among the opticians of London, its significance was soon grasped by a one John Dollond (1706–61), whose life is discussed in the author’s earlier book, Classic Telescopes (2013). After conducting his own set of experiments on achromatic doublets, Dollond presented his lenses to the Royal © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_6

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84 Fig. 6.1  The achromatic doublet object glass produced greatly improved image quality. (https:// en.wikipedia.org/wiki/ Achromatic_telescope#/ media/File:Lens6b-en.svg)

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Flint

Achromatic doublet

Fig. 6.2  John Dollond (1706–1761). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ John_Dollond#/media/ File:John_Dollond,_by_ Benjamin_Wilson.jpg)

Society in 1758 and shortly thereafter, his son, Peter Dollond, applied for a commercial patent to market the design. Moor Hall did twice challenge Dollond’s application for this patent on the grounds that he was the original inventor. He was unsuccessful, however, as the jury evidently decided that since the Dollond family were the first to demonstrate the technology to the general public, they had a greater legal right to commercially exploit it (Fig. 6.2).

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So began the extraordinary legacy of the Dollond telescope dynasty, which lasted right up until the beginning of the 20th century, and which brought the achromatic refractor to the world at large. It is easy to underestimate what the achromatic ­telescope did for astronomy, navigation and the technicalities of warfare. Suddenly, the refractor could be greatly shortened in focal length and still deliver good, sharp images, with greatly reduced aberrations. The Dollond family made an enormous fortune out of marketing the achromat, though when their patent ran out, opticians around the world started producing their own renditions of the achromatic telescope, driving prices down and allowing common people to enjoy their considerable advantages. It was into this exciting new world that Charles Messier came of age. Born in Badonviller, part of the then kingdom of France on June 26, 1730, Charles was one -of 12 children of Nicolas and Francoise Messier, a middle class family supported by their father’s reasonably well paid job as court usher to the regents of Salm, a principality of the Holy Roman Empire, which then included Germany, France and Luxemburg. Like any large family of the day, sibling death was all too common, and Charles had already lost half his brothers and sisters by the time his father died in 1741, when Charles was still but a boy of 11 years. His eldest brother, Hyacinthe, took over the head of the family, as was the custom in those days, and was lucky enough to secure a clerical post in the same court his father served in at Badonviller. But other events helped shape the future of the young Charles, who, aged just 10, had broken his two legs as a result of falling from a high window at his home. The prolonged convalescence required that he be home-­ schooled by Hyacinthe, a duty that he continued for the next decade, and which provided Charles with a thorough grounding in clerical and administrative work that would serve him well in his future astronomical career (Fig. 6.3). The key event that would stoke Charles’ lifelong dedication to the night sky was a magnificent six-tailed comet that lit up the sky over Lorraine in 1744. The comet (C/1743X1), named after its discoverer, Jean Philippe Loys de Chesaux, a wealthy Swiss mathematician, outshone the brilliant planet Jupiter in the night sky and filled the young Messier with awe and wonder. And just a few years later, an annular solar eclipse occurred over Bardonviller on the afternoon of July 25, 1748, plunging the town into gloomy duskiness for a few minutes. It was clear to Charles, (now 18 years old) that the heavens were summoning him to discover more of her secrets. But it was another event, only superficially connected with astronomy, that consolidated Charles Messier’s future career as an astronomer. In 1751, a re-drawing was made of the political map of the region. Bardonviller was no longer under the jurisdiction of House of Salm. Hyacinthe, ever the loyal subject, followed his employer to Senones, situated between Nancy and Strasbourg. Charles stayed behind, seeking employment locally and turning to a kindly and influential man, Abbot Theolen, to help him secure employment. Theolen delivered, giving Charles the choice of not one but two decent posts, the first as an assistant to a local curator and the other an opportunity to work with the astronomer Joseph Delisle (1688– 1768), who not so many years before confirmed Comet de Chesaux’s six-tailed

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Fig. 6.3  Charles Messier (1730–1817), aged 40. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Charles_Messier.jpg)

morphology. On the advice of his elder brother, Charles made the fateful decision to work for Delisle, but this entailed moving to the great city of Paris. Messier began working for Delisle on October 2, 1751, at an observatory established on the rooftop of Hôtel (townhouse) de Cluny, which was rebuilt in the end of the 15th century on the ruins of an ancient Roman building and was now run by the French navy. Almost immediately after commencing work with Delisle, Messier made an impression; in particular the astronomer was struck by the neatness of his handwriting, a skill he doubtless learned from Hyacinthe. Having no children of his own, Delisle took Messier under his wing, becoming like a father figure to the 21-year-old and even offered him lodgings in the nearby Royal College of France, where he and his wife were settled. His first assignment under Delisle had nothing to do with astronomy, however, but instead involved copying out a map of China dating from the third century b. c. Soon, though, he settled into routine work, recording all of the astronomical observations made by Delisle, who had designed and built the observatory, erected on the roof of the Hôtel de Cluny in 1748, which was fashioned from wood and glass into a pyramidal framework with opened windows. The observatory itself was reasonably well equipped with a number of moderate aperture reflecting telescopes with speculum mirrors. One had an aperture of about 8 inches with a focal length of 53 inches, but the one that Charles grew most fond

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of was a 6-inch Gregorian. The effective light-gathering power of these instruments was very modest, however, as each speculum mirror only reflected about 60 percent of light incident upon them, and further declined by another 10 percent after only a few years of use in the open air. As a result, the effective light-gathering power of these instruments was equivalent to a modern 3.5-inch (9-cm) refractor. Delisle also had a personal assistant called Libour, who prepared the telescopes for observation, and Messier became especially keen to learn how to operate them himself. As soon as Libour showed him the ropes, Messier began making his own observations, the first of which was the transit of Mercury, dated to May 6, 1753. Accurate recordings of these transits helped refine planetary orbits as well as fine tuning the predictions of future transits. By 1755, Messier had established himself as one of the most experienced observers of his time, having then compiled a list of 41 objects for his famous list, 17 or 18 of which were brand new discoveries. For this work Messier was promoted to depot clerk of the navy, having his board and lodgings paid for and enjoying a modest salary of 500 francs per annum. One of the biggest unanswered questions in astronomy in Messier’s day pertained to the origin and nature of comets. Were they random visitors to the Solar System or did they have proper orbital periods just like the planets? This was precisely the question posed by the British astronomer, Sir Edmund Halley, back in 1701. While calculating the orbit of a comet that appeared in 1681–82, Halley noticed something unusual. His computations seemed to match those of a comet that entered our skies back in 1531, which had been studied in great detail by the German astronomer, Petrus Apianus. But it also matched the characteristics of yet another comet seen by Johannes Kepler in 1607. All these comets appeared roughly 76 years apart, leading Halley to make a bold leap in thought; perhaps these comets were in fact one and the same? (Fig. 6.4) But Halley’s conjecture went against the grain. Up until that time, comets were thought to be unique objects, appearing haphazardly in the sky before disappearing like a proverbial black dog in the night. Moreover, if comets did exhibit such periodicity, then they must necessarily be a legitimate part of our Sun’s family, and thus subject to the same laws of planetary motion enunciated by Kepler at the beginning of the 17th century. Halley had predicted that the same comet would return in late 1758 or early 1759, though he would not be around to observe it himself. News of Halley’s prediction spread like wildfire across Europe, and Messier took it upon himself to begin a systematic search for the comet as early as 1757. Aided by Delisle’s own calculations, Messier put together beautifully crafted maps of the sky replete with the mythical figures of the constellations they contained, and began to scan these regions, as well as venturing into areas of sky outside of those designated by Delisle, for signs of the interloper using the observatory’s 53-inch focus Newtonian. Though he was not proficient at mathematics (in contrast to Delisle), Messier made up for this deficiency by his methodological rigor and enthusiasm, conducting prolonged observations every clear night. Sometime during 1757, he chanced upon a fuzzy, luminous object in the constellation of Andromeda. But as he looked more closely at the object, he suspected something was amiss. For one thing, the object was nowhere in the vicinity of where

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Fig. 6.4  Hôtel de Cluny as it appears in the present day. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Mus%C3%A9e_de_Cluny_%E2%80%93_Mus%C3%A9e_ national_du_Moyen_%C3%82ge#/media/File:Paris_2012-aout-0006-2-Hotel-de-Cluny.jpg)

Halley had predicted the comet to be, and it didn’t move relative to the fixed stars in the way a comet usually does. Later he cataloged this object as number 32 on a list he was compiling. Then, on August 14 of the same year, Messier tracked down yet another nebulous object. This time, it was moving like a comet, which must have made his heart race, but when he checked its orbital path on his star charts, it did not match up with anything. Had he discovered a new comet of his own? Alas, no. The comet observed by Messier that fateful August evening was C/1758 K1 de la Nux, which was discovered back in May 6, 1758. Nonetheless, he kept up observations of this comet for a few weeks, and on August 28 he came across yet another faint fuzzy in the constellation of Taurus, very near the star Zeta Tauri, an object he later recorded as number one (M1) on his list. This turned out to be a hitherto unobserved object, one of many that would secure Messier’s fame in the annals of astronomy. For this work, the French king, Louis XV, even nicknamed him the “ferret of comets.” Incidentally, the exact position of M1 corresponded to the locus of a bright guest star that appeared in Taurus seven centuries before Messier’s discovery. We know this object today as the Crab Nebula, the remnants of a supermassive star that blew itself up, brightening so much that it was possible to read by it at night. Its modern appellation was bestowed upon it by Lord Rosse in 1844, after he sketched the object as seen through the 36-inch reflector at Parsonstown, Ireland (now Birr Castle).

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Despite his diligent searches within the strips of sky advised by Delisle, Messier had thus far failed to observe the comet predicted by Halley. So he began to search regions of sky outside those already combed through. His fortunes changed on the night of January 29, 1759, when he spied a fuzzy object on the periphery of the field served up by his comet-seeking telescope, and almost exactly 2 years after he had begun his searches. Keeping his cool, Messier carefully charted the object’s movement against the background stars, and consulting the calculated orbital trajectory as provided by Halley, he was sure that he had caught sight of the famous comet, fully 52 days before its perihelion passage. It turned out that Delisle’s calculations contained a small error that underestimated the gravitational effect of Jupiter in perturbing the orbit of the comet, offsetting its course. In contrast, Halley’s original calculations had placed it quite near where it was actually found! But while this ‘discovery’ should have been a cause of celebration, Delisle took it to heart, insisting that he had not made a mistake in his calculations and refused to publically announce its return to the inner Solar System. Messier, ever the loyalist, accepted his superior’s decision and kept the discovery secret. In retrospect, though, because the masses of the planets, including giant Jupiter, were not known with any great accuracy, and given that even skilled celestial mechanicians, such as Jerome Lalande (who had also worked at the Hôtel de Cluny), could not have accurately predicted the time and place of return of Halley’s Comet even to within months, this seemed like an overly harsh reaction by Delisle. Indeed, Messier later elaborated on his superior’s embargo on the public announcement of the return of Halley’s Comet, writing in the Connaisance de Temps (1810): The whole day was very fine and without cloud: in the evening I went over the sky with the telescope, keeping the limits of the two ovals drawn [by Delisle] on the celestial chart which was my guide. At about six o’ clock I discovered a faint glow resembling that of the comet I had observed in the previous year; it was the Comet itself, appearing 52 days before perihelion! There is cause to presume that if Delisle had not made the limits of the two ovals so restricted, I would have discovered the comet much earlier.

The delay in announcing Comet Halley’s return from the astronomers at the Hôtel de Cluny was of little importance, for it turned out that Messier had been once again beaten to it by the efforts of the German farmer and amateur astronomer living near Dresden, Johan Palitzch, who recovered the comet on Christmas Day 1758, which brought him international fame. Halley had been correct all along; comets are integral parts of the Solar System, obeying the same laws of motion that define the orbits of the planets and their satellites. Furthermore, it vindicated the physics of Newton, which provided the explanatory power of orbital prediction. Although Messier was somewhat frustrated by Delisle’s decision not to announce the recovery of Halley’s Comet, he put it behind him and continued his vigils of the night sky. This time though, success came early, for in January 1760 Messier discovered his first comet, designated C/1760 A1, which turned out to be the finest one of the year, with its 5-degree-long tail. Remarkably, Delisle once again refused to give Messier permission to publish his discovery but eventually gave in to his requests. Indeed, shortly afterwards, the aging chief astronomer at the Hôtel de Cluny consented to allow Messier to take over the day-to-day running of the obser-

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vatory, and he was thereafter free to carry on his own observations without interruption. In the immediate years that followed, Messier’s diligence as an observer brought new discoveries to his tally, finding two new comets – C/1763 SI and C/1764 A1 – on September 28, 1763, and January 3, 1764, respectively. On the back of his discoveries, Messier sought formal recognition for his work and applied for membership in the prestigious French Royal Academy of Sciences. But like many of these institutions at the time, he met with considerable opposition from some of its members, who felt that since he was not a classically trained astronomer, proficient in the mathematical methods of the day, he was not worthy of membership. Not surprisingly, his application was turned down. However, he was elected to the British Royal Society in 1764 in recognition of his comet discoveries. Not one to be put down by the pomp and ceremony of the French scientific elite, Messier pressed on with his telescopic observations, adding a further 20 ‘nebulae’ by 1765 to his now famous list, including M42, the Great Nebula in Orion, the Beehive Cluster (M44) in Cancer and M45, the Pleiades cluster in Taurus. Of course, there was great diversity in these objects – open and globular star clusters, supernovae remnants, galaxies and bona fide nebulae – but their precise nature was immaterial to Messier, since he compiled this list so as not to confuse them with new comets, which he expressly wished to discover more than anything else. It was around about this time that Messier began to have correspondences with other astronomers across Europe, and his election to both the British and Dutch scientific societies helped him to open new doors. The year 1766 was another prodigious one for Messier. On March 8 he discovered yet another comet, C/1766 E1. Intriguingly, he actually spotted it with his naked eye before confirming it telescopically. This was followed by his co-­discovery of comet C/1766 G1 the following month with its co-discoverer, Johan Helfenreider. With every new object he added to his name, Messier’s fame grew, and with an ever-­ increasing circle of acquaintances who might call on his services. In 1767 Messier was approached by the distinguished French horologists, Julian and Pierre Le Roy, who hired him to conduct observations out at sea in order to assess the accuracy of newly constructed naval chronometers. This was the first sea voyage Messier would undertake. The Le Roys, like John Harrison in England, had also been working on the longitude problem and had been developing accurate timepieces that would work well at sea. Since Earth rotates at a steady rate of 360° every day, that amounts to 15° per hour (in mean solar time). There is a direct relationship between time and longitude. If the navigator knew the time at a fixed reference point when some event occurred at the ship’s location, the difference between the reference time and the apparent local time would give the ship’s position relative to that fixed location. Working out apparent local time is relatively easy using a sextant. The problem, ultimately, was how to determine the time, while onboard a ship, of a distant reference point. One way forward was to have an accurate chronometer set at the local time at a fixed location, which traveled along with the ship. Thus, whoever could keep sea time accurately would have mastery of the oceans, as well as the world’s

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naval trading routes. John Harrison’s timepiece, H4, was famously tested on a trip to Barbados just 3  years before and showed encouraging results, but the French were determined to develop their own timepieces, and this latest chronometer was considered the equivalent of H4. The mission entailed a four-month voyage through the frigid waters of the Baltic Sea, where Messier carried out sextant measurements to ascertain local time, which in turn were compared with the time recorded using the Le Roy chronometer. Using a sextant at sea was far from superficial, however, but the French navy was confident that if anyone could succeed at it, Messier could. He sailed on board L’Aurore (The Dawn), accompanied by Alexander-Guy Pingre, who would carry out the calculations. The expedition was generously funded by the Marquis de Courtanvaux. Meanwhile, Lalande would take over the day-to-day running of the observatory at the Hôtel de Cluny. By all accounts, while Messier was happy to be of service to his maritime friends, he did not enjoy the sea voyage and was keen to return to terra firma once the expedition ended. More success followed on the heels of Messier’s early comet finds, for on August 8, 1769 he discovered the most spectacular comet of that year, designated 1769 Messier in his honor. Sending news of his discovery to the Frederick II, king of Prussia, the monarch was so impressed that he used his considerable influence to have Messier elected to the prestigious Berlin Academy of Sciences on September 14, 1769. By March 1771, Messier had compiled a list of 45 objects, which were published by the Academy of Sciences. He also had no fewer than eight comet discoveries to his name. This was enough to have Messier appointed to the post of Astronomer to the Navy, which gave him ample time to continue his famous comet sweeps, as well as performing his ‘official’ duties. By the middle of April 1781, he had logged his 100th comet-like object, but instead of leaving it at that, he decided at the last minute to include a further three objects that had been discovered by Pierre Mechain between 1780 and 1781. Perhaps the most insightful entry is that of M73 in Aquarius, which appears as merely a quartet of stars to the contemporary observer equipped with a modest backyard telescope. That Messier felt the need to list this as a nebula indicated that the instrument he employed – probably a reflecting telescope of sorts – to observe it was very crude by modern standards. The same is true of a few other Messier objects, including M47, M48, M91 and M102. Mechain had been newly employed at the Hôtel de Cluny as ‘calculator’ and assistant to Messier but was also a very accomplished visual observer in his own right, eventually adding three newly discovered objects to Messier’s list: M105, M106 and M107 in 1783. Indeed, he had distinguished himself enough to be elected as a member of the Academie des Sciences in 1782, in honor of his own comet discoveries. The 103 objects formed the corpus of his completed list, published in the Connaissance des Temps in 1783. These are the celebrated Messier Objects amateur astronomers across the world have visited time and time again ever since, and cover an area of sky running from the north celestial pole to as far south as −35.7° declination. Having said that, there are a number of objects that Messier failed to include

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Fig. 6.5  A small refracting telescope by Dollond, similar to the best telescope used by Charles Messier. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ File:Telescope_by_John_ Dollond_in_VULibrary. JPG)

in his catalog, even though they would have been readily visible through the telescopes he used. These include objects such as the Double Cluster in Perseus, the open cluster NGC 6231  in Scorpius and the edge-on spiral galaxy, NGC 891, in Andromeda, to mention just a few. Messier’s earliest experience with telescopes involved those of the reflecting type – either Gregorians or Newtonians – neither of which were very efficient. But archivists now believe he used a variety of refracting telescopes of both the singlet and doublet variety. Indeed, in all, just short of a dozen telescopes have been associated in one way or another with Messier’s observational career. These included a few long focal length non-achromatic refractors, a few early achromatic doublets with one fashioned by Dollond of England, a 6-inch Newtonian reflector with speculum mirrors, and a Gregorian telescope of 6  feet focus. Magnifications ranged from about 40× up to 150× (Fig. 6.5). Of all the telescopes he used, however, it was the achromatic refractor that he held in highest esteem: “It were wished that astronomers, concerned in observations, might be accompanied with achromatic telescopes of the most perfect construction; as such are the only instruments whereby a great knowledge of the celestial bodies can be acquired, for the improvement and perfection of astronomy.”

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One can readily understand Messier’s endorsement of the achromatic. Compared to the reflectors of the day, its efficiency in regard to light transmission was far greater than the best speculum mirrors that could then be produced. Moreover, in comparison to the exceedingly long and unwieldy singlet refractors that dominated the late 17th century and early 18th century, the achromatic doublet was far more convenient to use. It was while using his handy achromatic refractor that Charles made arguably his most intriguing comet discovery, first seen on the evening of June 14, 1770. Curiously, it was called Messier’s Comet for a short spell until the limelight was shifted to the Finnish mathematical astronomer, Anders Lexell, who worked out both the shape and period of the comet’s orbit – just 5.6 years. This was a far shorter orbital period than any cometary orbit that had hitherto been calculated. What’s more, the same comet disappeared completely in the years that followed, never again to return. This has led some modern commentators to suggest that Comet Lexell was captured and swallowed up by Jupiter, sharing the same fate as Comet Shoemaker-Levy 9 (discussed in a later chapter), after it crashed into the planet back in July 1994. Messier was electrified when he heard of the discovery of a strange comet, first seen by the Anglo-German astronomer William Herschel on March 13, 1781. Postponing his regular work, he observed the object during April of the same year and detected a small amount of motion relative to the background stars. He passed on his observations of ‘Herschel’s comet’ to his friend, the mathematician and judicial president of the French Parliament, Jean Baptiste-Gaspard de Saron. He also wrote directly to Herschel in England, praising his work: “It does you the more honor as nothing could be more difficult than to recognize it and I cannot conceive how you were able to observe it several days in succession to perceive that it had motion, since it had none of the usual characteristics of a comet.” With the aid of de Saron and Lalande, Messier established that the kinematics of what the world would shortly know as the planet Uranus was quite un-comet-like and that it must be a planet located well beyond the orbit of Saturn! Incidentally, Herschel was not the first to glimpse Uranus, as it was very likely observed by Galileo in the early 1600s and at least six times by John Flamsteed, as early as 1690, who prematurely dismissed it as the star 34 Tauri. After similar observations were conducted by other astronomers across Europe, Herschel’s new planet was universally confirmed, and though he initially bestowed the appellation of Georgium Sidus upon it, in honor of his patron, the reigning British monarch George III, it was officially named after the ancient Greek deity, Uranus, the father of the god Saturn (Cronus). In November 1781, more trouble beset Messier, when he endured a second serious fall, this time through an ice cellar 25  feet deep, breaking his leg, wrist and several ribs in the process. The ordeal left him bedridden for several months. Indeed, Messier was unable to walk again for another year, and only then with a pronounced limp. Messier began active observing in November 1782, when he recorded the transit of Mercury. Like many astronomers of his day, he entertained the idea that another planet lay in waiting to be discovered inside the orbit of Mercury, and

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despite quite extensive searches, his efforts turned up nothing. Soon after this, he went back to his favorite pursuit, comet hunting, discovering several more over the next 5 years. By this time, however, the political climate of France was changing rapidly, as the bourgeois and peasantry were becoming more and more disaffected with the noble classes and the enormous national debt built up by Louis XV’s wars, both with neighboring nations and overseas in the many colonies of the French empire. The price of wheat skyrocketed, and many of France’s sons and daughters were driven to abject poverty. This was the desperate situation inherited by Louis XVI and his infamous queen, Marie Antoinette, who, instead of trying to solve France’s economic problems, considerably worsened them out of nothing more than personal greed and her somewhat delusional claim to be part of the Ancien Regime. Events came to a head on July 14, 1789, when an angry militia stormed the Bastille Saint-­ Antoine, a small Parisian prison, in order to gain access to its stockpile of arms and ammunition. The bloody French Revolution had begun. Messier’s post as Astronomer of the Navy was terminated, as no funds were made available to maintain the upkeep of the observatory at the Hôtel de Cluny. He had hoped that the political unrest would be short-lived, but ‘le Terreur’ of the Revolution only escalated. In January 1793 Louis XVI was guillotined and his queen followed suit in October of the same year. Remarkably, though, despite the turmoil, Charles continued his astronomical work, observing his 36th comet on September 27, 1793, and sending detailed notes of his nightly vigils of the comet to a now imprisoned De Saron, who was only too glad to focus his mind on such things, knowing that he awaited execution. Neither was Messier’s assistant, Pierre Mechain, immune to the consequences of the Revolution, having being unjustly imprisoned as an “anti-revolutionary spy.” And though he was later released, his family lost much of their wealth and landholdings to the ringleaders of the Revolution. Despite no longer having a salary or even a pension, Messier and Mechain continued the love of their lives – hunting for comets – even as the Revolution reached its bloody peak with the rise of Napolean Bonaparte. In the aftermath of le Terreur, both Messier and Mechain were awarded membership of the newly -named Academy of Sciences, and both served on the French Board of Longitudes. Napolean, eager to reward scientists on merit alone, personally awarded Messier with the Cross of the Legion of Honor in 1808. Charles was deeply moved by the gesture, and now aged 78, he truly felt that he had achieved the international fame and respect he so badly craved. With the financial help of influential friends, he lived out the remainder of his life in relative comfort, though his slowly failing health meant that he could not observe anything as frequently as he used to. In 1815, he suffered a stroke, which left him paralyzed, and he died 2 years later on April 11, 1817. What is Charles Messier’s legacy? As well as completing a catalog (together with Pierre Mechain) of 103 deep sky objects, he tracked and observed 44 comets, of which 13 were his own discoveries. His list of deep sky objects has been recognized by astronomers, amateur and professional, ever since. Whether it be the Reverend William Rutter Dawes or Edwin Hubble, both knew the Great Nebula in Andromeda as Messier 31. Further objects were added to Messier’s list after his

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death, including those discovered by Mechain and overlooked objects originally recorded by Messier. By 1966, the list had grown to 110, and that number has remained the same ever since. The lunar crater, Messier, and the asteroid 7359 Messier were also named in honor of the great man. Messier’s draughtsman-like work was an inspiration to other astronomers to carry out their own surveys using ever better instruments. For the contemporary reader, or amateur astronomer possessing a modest telescope, Messier showed that one could achieve a great deal with very humble instruments, the likes of which would be considered downright shoddy today. Then, as now, diligence and devotion to the task at hand were more important than anything else. The new discoveries wrought by the development of the telescope also caught the ear of giant political figures in the history of world; and just one of them was the great American statesman, Thomas Jefferson, who we will discuss in the next chapter.

Sources English, N.: Classic Telescopes. Springer, New York (2013) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) King, H.C.: The History of the Telescope. Dover, New York (1955) O’Meara, S.J.: The Messier Objects. Cambridge University Press, Cambridge (1998) Pugh, P.: Observing the Messier Objects with a Small Telescope. Springer, New York (2012) Rousseau, P.: Man’s Conquest of the Stars. Jarrolds, London (1959) Messier’s Telescopes. http://messier.seds.org/xtra/history/m-scopes.html

Chapter 7

Thomas Jefferson and His Telescopic Forays

Thomas Jefferson is well known as an American Founding Father, the principal author of the Declaration of Independence and later served as the third president of the United States, from 1801 to 1809. Prior to that, he was elected the second vice president of the United States, serving under John Adams from 1797 to 1801. Brought up in Shadwell, Virginia, he was of English and Welsh ancestry and was born a British subject. A towering intellect, Jefferson was a proponent of liberal democracy, republicanism and individual rights motivating American colonists to break the yoke of British rule. Trained in jurisprudence, Jefferson produced formative documents and decisions at both the state and national level (Fig. 7.1). An owner of several large plantations worked by hundreds of Negro slaves, Jefferson was a complex character who enjoyed many hobbies allied to scientific advancement. Indeed, he actually considered himself to be a scientist, though he received no coherent training in any of its disciplines. He was reputed to have spoken and written in six languages, including ancient Greek and Latin. But he was also an inventor of some repute, creating the world’s first revolving bookstand. He also made improvements to the pedometer and a polygraph, a device for duplicating writing and had more than a casual interest in astronomy. “Nature intended for me the tranquil pursuits of science by rendering them my supreme delight,” he wrote in an 1809 letter to Pierre Samuel DuPont de Nemours. For Jefferson, astronomy was always about looking up. The voluminous correspondences uncovered by historians reveals Jefferson’s considerable interest in the work of other inventors, and significant interaction with the inventors themselves. Jefferson mastered many disciplines, which ranged from surveying and mathematics to horticulture and mechanics. One of these interests was the development of the telescope, and in particular, the refracting telescope. As described in more detail in this author’s earlier work, Classic Telescopes, Jefferson expressed a keen interest in the British firm John Dollond & Sons, who had brought the achromatic refractor to market beginning with Dollond’s securing of a lucrative patent to construct such instruments in 1758. Jefferson became a keen stargazer and

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Fig. 7.1  Thomas Jefferson (1743–1826), Statesman and amateur astronomer. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File%3AOfficial_ Presidential_portrait_of_ Thomas_ Jefferson_%28by_ Rembrandt_ Peale%2C_1800%29.jpg)

enjoyed observing the heavens with his Dollond refractor, which he used at his opulent estate at Monticello in Charlottesville, Virginia. Though the achromatic doublet, consisting of crown and flint elements, was a huge improvement over the singlet objectives used so successfully by Huygens and Hevelius, among others, Dollond experimented with ways of further reducing the focal length of his telescopes by introducing yet another crown element in order to improve the residual spherical aberration inherent to the achromatic doublet design. This third element increased the so-called number of degrees of freedom to the objective, allowing him to reduce the curvature of the four crown surfaces and thereby reducing geometric aberration still more. But Dollond achieved only limited success with this, and invariably the apertures on these early triplets were very small. To add insult to injury, Dollond’s advancing age meant that he could no longer expend the energy to develop such triplet achromats into a commercial success. It was left to his son, Peter Dollond, to carry on this work, and towards the end of his life, he had apparently managed to construct a number of 95-mm triplet refractors that were almost color free with improved corrections for spherical aberrations. Unfortunately, not many of these instruments were made owing to the greatly increased difficulty of their construction, as well the new competition from the improved reflecting telescopes being constructed by William Herschel. Consequently, Peter Dollond reverted to manufacturing long focal length achromatic doublets as these seemed to satisfy the vast majority of common observers.

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Perhaps the best documented example of such triplet optics is the telescope acquired by the Reverend Francis Wollaston, himself a keen amateur astronomer, in 1771, which had a clear aperture of 90.2 mm with a focal length of 1.143 m. This gave fine, high power images with significantly reduced secondary spectrum and spherical aberration over a conventional achromatic doublet. In 1786 Thomas Jefferson visited England, stopping off first in London, where he paid a visit to the workshops of Peter Dollond. On April 26, 1786, Jefferson left the capital of the British Empire, bound for Paris (he served as the U. S. minister for France between 1784 and 1789) with a newly purchased £10-10 telescope possessing a triplet objective in his baggage. He was accompanied by his comrade, John Paradise, who apparently introduced him to Nevil Maskelyne, the Astronomer Royal since 1765. Maskelyne gave his esteemed visitors a tour of Christopher Wren’s main building at the observatory, with its octagonal Great Room, and the new observatory containing a time-keeping transit instrument as well as the 8-foot mural quadrant first used by Edmond Halley back in the day. Jefferson may also have made the climb to the roof to inspect the camera obscura Maskelyne had installed in the turret room. Since its founding day in 1675, the Astronomers Royal resident at Greenwich Observatory had been engaged in mapping the heavens, carefully recording the positions of thousands of the ‘fixed’ stars. Maskelyne’s passion, though, was understanding the detailed kinematics of the Moon. Tracking its daily passage over the meridian was part of the mission of the Royal Observatory, as outlined by Charles II a century before to consult the heavens “so as to find out the so much desired Longitude of Places for perfecting the art of Navigation.” Jefferson’s own scrutiny of the lunar regolith and other heavenly bodies had begun early in his long life. It was William Small, his professor of natural philosophy at his alma mater at the College of William and Mary, who had provided him his “first views of the expansion of science and of the system of things in which we are placed.” Jefferson was of course referring to the beautiful and rational order of the laws of nature as enunciated by Sir Isaac Newton. Jefferson came to regard astronomy as the “most sublime of all sciences,” and naturally enough, it was to become his favorite portal to the harmonious universe governed by the precise clockwork of Newtonian mechanics. This view also informed his theology; the Biblical God created the universe and its rigorous laws were upheld without His intervention. At home in Virginia Jefferson and his old school pal, John Page, would sometimes pass a few idle hours stargazing from the roof of Rosewell, the Page residence near Williamsburg. Jesting with his friend in 1770 for his ineptitude as a correspondent, Jefferson quipped that Page’s head was “always in the moon, or some of the planetary regions.” In the same letter, laced with various astrological allusions, Jefferson figured that if he and Page spent too much time stargazing, the gods might fear that they would “pull down the moon or play some such devilish prank with their works.” In 1793 Jefferson acquired a second Dollond telescope for an undisclosed price. Both instruments survive and indeed can be seen at his home at Monticello, which

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Fig. 7.2 Thomas Jefferson’s hand telescope. (Image courtesy of Thomas Jefferson Foundation at Monticello)

is now a museum, although it is still debatable as to which instrument he acquired first. In 1793 Jefferson bought what was to be the most valuable telescope in his collection, an equatorial by the famous London optician Jesse Ramsden (1735– 1800), whom he considered preeminent among optical artisans. With “this noble instrument,” as he proudly referred to it, he fixed the meridian at Monticello and viewed the annular solar eclipse of 1811. Judged by one observer to be “unquestionably the most sophisticated instrument in the United States” at the time, Jefferson’s equatorial was the foundation of his favorite theory of a method for determining longitude by lunar distances which did not require a timepiece. In order to work this important number out, two things are required; first one needs an instrument for observing and measuring angles. This was achieved by the invention of the octant, which had become an important maritime instrument by the middle of the 18th century. The second element required the most accurate tables of the motion of the Moon among the fixed stars, but even in Jefferson’s day, this was not fully understood. Indeed, we now know that our natural satellite obeys a system of motion that repeats every 18  years but in such a complicated way that even geniuses such as Isaac Newton could not fully comprehend. Nonetheless, the refined work of astronomers of the ilk of Tobias Mayer had produced lunar tables accurate enough to determine longitude at sea. Indeed, Neville Maskeylyne had used Mayer’s lunar tables on expeditions to St. Helena and Barbados in 1761 and 1763, respectively. Indeed, the Board of Longitude awarded Mayer’s widow £3,000 in recognition of her late husband’s work (Fig. 7.2). Although the lion’s share (£20,000) of the prize for establishing a reliable way of determining longitude was awarded to the British horologist, John Harrison, the lunar method continued to be practiced well into the 19th century. Indeed, it was the method most favored by Jefferson, who noted in 1822 that comparing the times of the same “celestial phenomenon” at two different points provided the difference in longitude. He considered the Moon as the best heavenly body for the job, as it was large and bright and its motions were large enough to be measured on a daily basis.

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From 1767 onwards, the Moon’s position was measured eight times a day, based on the time kept by the clock at the Royal Observatory at Greenwich and the results tabulated in an almanac. Nevil Maskelyne was responsible for this compilation of the world’s collective astronomical wisdom, and Jefferson purchased some of these almanacs at Greenwich, dispatching them to his American friends on his return to Paris. The Nautical Almanac, and its companion Requisite Tables, reduced the lunar distance method from a 4-h to a 30-min operation. Nevertheless, the complexity of the calculations made “taking the lunars” a dreaded component of naval training. Regardless of which method Captain Wyatt St. Barbe employed on his transatlantic crossings in the summer of 1784, Jefferson was likely an observer. He came up on the deck of the Ceres to witness the ritual of the noon sighting, since he kept his own personal log of the voyage in which he recorded the daily latitude and longitude, as well as various meteorological parameters such as temperature and wind direction. He made many observations of maritime wildlife, including gannets and shearwaters, gulls, petrels, whales and sharks that surfaced near the ship during the three-week long passage from Boston to the Isle of Wight. On the Ceres Jefferson sailed through nearly 70° of longitude, moving ever closer to the zero of the Royal Observatory. Before the publication of Maskelyne’s nautical almanacs, the meridian at Greenwich was just one of many prime meridians. Afterwards the Greenwich meridian became the reference point for more and more mariners and mapmakers until, in 1884, it was officially accepted by a consortium of 22 nations as the basis for the world’s system of time. The French abstained, though, using Paris as their zero line of longitude until 1911. Jefferson set up his own meridians wherever he went. At his palatial country estate at Monticello he established its north-south line from his own calculations made in November 1778, and a year later, while in France, he asked the director of the Paris Observatory for precise times to compute his meridian at the Hôtel de Langeac. Little did Jefferson foresee that establishing a meridian would take on a political dimension some 15 years later, when he ascended to the office of president and first citizen of a new nation. Inspired by the launching of the Lewis and Clark expedition, Jefferson became ambitious to establish a suitable geography for an independent nation. “[W]e have done too little for ourselves, & depended too long on the ancient & inaccurate observations of other nations,” he quipped. American maps deserved an American prime meridian. He commissioned surveyor Isaac Briggs to lay out a meridian through the middle of the president’s house in Washington. This project lapsed, however, and the mysterious “Jefferson stone” near the Washington Monument remains as an unimpressive relic. But Jefferson, uniquely grasping the importance of ordinance surveys, realized that the situation of the United States, with its enormous expanse of unexplored land, demanded a complete rethinking about longitude. This was especially important in light of the 1803 Louisiana Purchase, which doubled the size of the United States literally overnight, and over which Jefferson presided. Up until then, the European nation-states, long established on a continent long settled and mapped, longitude was only important to their merchant and naval fleets at sea. But as more and more explorers and their

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families moved steadily westward over rocky mountains and vast open plains found themselves “changing their longitudes rapidly and at every step,” and so had entirely different priorities. New circumstances clearly called for new lines of longitude. Jefferson accordingly “sat himself” down and came up with a uniquely American method of finding the longitude in these new territories. It differed from the usual methods in not requiring a timekeeper, for he realized that in the vast western wilderness a chronometer would be subject to “a thousand accidents.” Its novelty consisted in the use of a meridian, because land observations permitted the calculation of this north-south sight line, an operation impossible at sea. The expeditious and trustworthy motions of the Moon and their Greenwich times revealed in the almanacs could then be observed in relation to the meridian. All of this depended, as Jefferson admitted, on the use of a very expensive and sophisticated instrument, of which the jewel of his own “Mathematical Apparatus” – a universal equatorial – was but one example. Jesse Ramsden (1735–1800) had perfected the equatorial mounting for a telescope in the 1770s. Its “combined motions” in three planes (horizon, equator and circle of latitude) made it extremely versatile and elegant, the “Questar of telescopes” back in the day. Jefferson had acquired his Ramsden equatorial in 1792, and sang the praises of “this noble instrument” for the remainder of his life. Jesse Ramsden was widely acknowledged as the leading instrument maker of his day. Born in Salterhebble, Yorkshire, the son of an innkeeper, he was educated at the Queen Elizabeth Grammar School in Heath, Yorkshire. He worked in London, initially apprenticed to Mark Burton, then for Peter Dollond, before establishing his own firm around 1762, competing with his erstwhile employer Peter Dollond, both of them working in the Strand. In 1766 he married Sarah Dollond, Peter’s sister, and continued working in London, later in Piccadilly, employing Matthew Berge, whose brother possibly was John Berge and worked for Peter Dollond. In 1786 he was made an FRS, and awarded the Copley Medal in 1792. Ramsden’s Universal Equatorial instruments were expensive, and appreciated by wealthy men. We do not know who first owned this state-of-the-art small telescope. But we do know that Thomas Jefferson had  one such instrument. The Ramsden telescope was probably about 16 inches long, possessing an achromatic objective with an aperture of 2.5 inches. There is a graduated circle for right ascension and another for declination, as well as a mechanism for adjusting the instrument for use at any latitude. The Ramsden telescope would have behaved much like a modern 60-mm achromatic refractor. The eyepieces used with the telescope were also likely of Ramsden design, consisting of two plano-convex lenses of the same glass and similar focal lengths, placed less than one eye-lens focal length apart. Ramsdens were an improvement over the Huygenian eyepieces used by all astronomers of the day but still inferior to later designs such as the Kellner and Plössl. That said, Jefferson’s equatorial would have delivered delightful views of the Moon, Saturn’s majestic ring system and the main belts and zones of Jupiter, along with its large satellites and was ideal for astronomical measurement.

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It was with the intention of calculating his own longitude at Monticello that Jefferson made preparations for an annular eclipse of the Sun that was to take place in the autumn of 1811. Two timekeepers and two observing instruments (a telescope and the great equatorial) were readied in preparation. Three additional observers were drafted, including President James Madison and his stepson, Payne Todd. On the morning of the eclipse on September 17, 1811, the instruments were brought to the viewing site – deployed in the midst of the late plantings of tennis ball lettuce and Swedish turnips in the kitchen garden. The garden terrace provided a clear view of the picturesque Willis Mountain 40  miles to the south, the sighting point for Monticello’s meridian. Jefferson’s remaining life was spent in the creation of the University of Virginia, which seems to have originated as a suggestion in a letter to the great American chemist, Joseph Priestly, in 1800. What is more, he firmly insisted that astronomy was taught at the University of Virginia, and he designed what may have been the first observatory in the United States. As a great admirer of the architecture of classical Greece and Rome, he insisted that its main buildings be stylized in like fashion. An adjacent hill on the site was purchased in order that an observatory and instruments be “prepared with the highest degree of skill and correctness.” These were ordered from the artisans of London, then the world center of astronomical learning. While awaiting the dividends of his detailed plans to come to fruition, Jefferson had drawn up a plan for the establishment of a temporary meridian at the portico of the Rotunda leading south through his “academical village.” As he contemplated future students ogling the Moon over this meridian, Jefferson may well have brought to mind an old question he posed to himself over half a century before. Captivated by the imagery of a 3rd century a. d. Scottish poet Ossian, Jefferson had transcribed into his literary commonplace book the opening lines of James McPherson’s Darthula: Daughter of heaven, fair art thou! The silence of thy face is pleasant. Thou comest forth in loveliness: the stars attend thy blue steps in the east. The clouds rejoice in thy presence O moon, and brighten their dark brown sides. Who is like thee in heaven, daughter of the night?

Jefferson penned a detailed account of the 1811 solar eclipse he had observed using a specially modified telescope. And throughout his administration, he instructed Meriwether Lewis (1774–1809), the explorer in charge of the Lewis and Clark expedition, to meticulously watch the stars and record their movement while exploring territories recently acquired through the Louisiana Purchase. Although “perspective” glasses and “pocket telescopes” make scattered appearances in Jefferson’s records, no certain reference to his portable spyglass can be found. That said, several family stories recount an intrepid Jefferson with spyglass in hand. In one curious account, Jefferson used his spyglass to observe British redcoats swarming in the streets of Charlottesville in 1781, an episode he barely escaped being captured by Tarleton’s dragoons. It is also very likely that he employed

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the same instrument during his leisurely walks on the North Terrace of Monticello to view the progress of the construction of the university he founded. Yet, during the four decades of his public service, Jefferson rarely found time to pursue his astronomical studies to any sustained degree. As he wrote in 1816, it is only by “interrogating the sun, moon, and stars” that we can know the “relative position of two places on the earth.” He repeatedly searched the sky to fix his own position on the ground and to contribute to one of his national goals – a “true geography” of his country.

Sources Bedino, S.A.: Thomas Jefferson: Statesman of Science. Macmillan, New York (1990) Chapman, A.: The Victorian Amateur Astronomer. Gracewing (2017) English, N.: Classic Telescopes. Springer, New York (2012) Sobel, D.: Longitude, New York Bloomsbury (1995) The Dollond/Wollaston Telescope. http://articles.adsabs.harvard.edu//full/1980JBAA...90..4 22D/0000422.000.html

Chapter 8

The Herschel Legacy

Any amateur astronomer with even a cursory interest in the history of the science will hold William Herschel, his sister Caroline, and his son John, in very high esteem. Widely regarded as the father of modern astronomy, William Herschel, together with his gifted son, greatly advanced our knowledge of virtually all arenas of observational astronomy, inventing whole new fields of inquiry, using homemade instruments that were much superior to anything that had come before. And Caroline, through her devotion to her brother’s work, as well as carrying out her own specialized investigations, is immortalized as one of the earliest female pioneers of astronomical science. That said, like so many other heroes and heroines of this era, their origins and rise to notoriety were more ordinary than extraordinary (Fig. 8.1). The Herschel family could proudly trace their ancestry back to the 17th century, where their great grandfather, Hans Herschel, owned a brewing business at Pirna, a small town in the German province of Saxony. Hans’ third son, Isaac, the father of William and Caroline, was born in 1707. After working as a landscape gardener, he turned his attention to music, quickly mastering the art and becoming a skilled oboist. Soon he put his new latent gifts to good use by joining the band of the Hanoverian Foot-Guards. But when Hanover became embroiled in the Austrian Wars of Succession, Isaac was compelled to accompany the Foot-Guards on campaign, which reached its climax with the defeat of the French army at Dettingen by an Anglo-Hanoverian force under the aegis of King George II. In the aftermath of this military campaign, Isaac Herschel returned home and married his sweetheart, Anna Ilse Moritzen, herself a native of Hanover, in 1732. They were blessed with ten children, of which only six reached the age of maturity. Friedrich Wilhelm (later Anglicized to William) Herschel was born on November 15, 1738. His younger sister, Caroline Lucretia, a dozen years his younger, was born on March 16, 1750. The children received their formal education at the Garrison School, but this was considerably supplemented by additional home-schooling from their father, who

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Fig. 8.1  William and Caroline Herschel polishing a telescope lens (probably a mirror), 1896 lithograph. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File%3AOfficial_ Presidential_portrait_of_ Thomas_ Jefferson_%28by_ Rembrandt_ Peale%2C_1800%29.jpg)

also endeavored to give them a good grounding in musical theory. But Isaac had other interests, cultivating more than a casual interest in astronomy, and was especially keen to impart his passion for stargazing to his children. Many years later, Caroline was to reminisce about those early days: My father was a great admirer of astronomy, and had some knowledge of that science; for I remember his taking me, on a clear frosty night, into the street, to make me acquainted with several of the beautiful constellations, after we had been gazing at a comet which was then visible. And I remember with what delight he used to assist my brother William in his various contrivances in the pursuit of his philosophical studies.

At age 14, William joined his father and his older brother Jacob in the regimental band as an oboist, and in 1756 they set out for Kent, in southeast England, where the regiment was stationed temporarily as a precautionary measure against the imminent threat of a French military invasion. Here, over the next few months, the Herschels immersed themselves in British culture, with William and Jacob learning to write and speak English and forging strong friendships with local musicians. Alas, this relatively pleasant stay in England wasn’t to last, and they soon found themselves back in Hanover and almost predictably, were caught up in yet another

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military campaign, which saw them accompanying the army against the French in the Seven Years War, which unfortunately ended in disaster for the Hanoverians. Although William marched with the Guards, he was in fact too young to properly enlist, and his father took this opportunity to advise him to leave the service and seek his fortunes in the musical business. Shortly thereafter, William sojourned to Hamburg, where he met up with his brother, Jacob, and together they resolved to return to England, making their way to London in the autumn of 1757. Around about the same time, the Hanoverian Guards, of which their father was still a member, were captured and placed under arrest by the invading French forces. However, after the French defeat at the Battle of Minden in 1759, they were released, and Isaac was finally able to return home in peace. The brothers Herschel arrived in Britain without much money but nonetheless managed to rapidly establish themselves with the help of funds generously provided by friendships forged on their maiden visit. They found work as musicians in various orchestras, and they were able to supplement their income by providing private tuition to paying customers. In the autumn of 1759, Jacob was informed by letter that he had secured the post of court musician back in Hanover and, sensing an opportunity for advancement, immediately returned home. William stayed in Britain though, securing a post of bandmaster of a regiment of militia under the supervision of the Earl of Darlington, which was stationed at Richmond, Yorkshire. William soon tired of this post however, and terminated his contract with them, returning to freelance musical work in a number of towns and cities in the northeast of England including, Newcastle, Leeds, Pontefract and Halifax. Herschel was also a very accomplished composer producing a number of concertos and symphonies commissioned by various patrons but supplemented this income by taking on private, fee-paying pupils. Herschel maintained this rather nomadic way of life for the best part of a decade or so, but during that time had made acquaintances with many influential individuals, including the Scottish philosopher, David Hume, and the musically -minded Duke of York, brother of the British sovereign, George III. During his sojourns across Britain, Herschel continued to educate himself by refining his knowledge of the English language – both spoken and written. He also taught himself Italian, long considered the lingua franca of music, and even brushed up on his classical Latin, still the formal language of the scientific establishment. In 1767, Herschel secured the post of organist at the Octagon Chapel in Bath, a fashionable city nestled in the heart of the English West Country. He continued to take on private pupils, which earned him quite a comfortable living. This new settled lifestyle enabled his brothers in Germany to come visit for extended periods, and in 1772, William himself embarked on a tour of the continent, visiting Paris and Nancy, before travelling home to his native Hanover. By this time, his youngest sister, Caroline, had come of age and was now keeping house for her aging mother and spendthrift brother, Jacob. William seems to have always had a special relationship with Caroline, and sensing her frustration with the drudgery of household work, he invited her back to England with him in the hope that she might embark on her own musical career. Caroline warmly accepted her brother’s ­suggestion, and soon she was earning her own way as a vocalist, helping to train her brother’s Octagon Chapel choir (Fig. 8.2).

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Fig. 8.2  Original manuscript of Herschel’s Symphony No. 15 in E flat major (1762). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/William_Herschel#/media/File:William_ Herschel_-_Symphony_No._15_-_British_Library_Add_MS_49626_f25r.jpg)

It was around this time that Herschel rekindled his interest in astronomy. In particular, after reading a book by a one Dr. Smith on musical harmonics, he became intrigued by another title by the same author on optics and astronomy. This prompted Herschel to begin his own study of the heavens, in February 1766, when he carried out observations of the planet Venus as well as a lunar eclipse. Following instructions given in Dr. Smith’s book, Herschel began to try his hand at making his own crude telescopes and used them to carry out his first astronomical observations. Over the next decade, however, astronomy remained, by necessity, a sideline activity in his life, as he sought to advance his musical career. For example, in an early diary dated to 1774, we are informed that Herschel was still giving up to eight private music lessons per day, but at night he would turn his attention to the starry firmament. Very soon, though, his infectious enthusiasm for stargazing even led some of his pupils to take lessons in practical astronomy from him rather than musical instruction! After enjoying a brief career as a vocalist, Caroline found herself spending more and more of her time assisting her brother in his growing fascination for all things astronomical. Soon, however, she would prove indispensable to him, accurately

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Fig. 8.3  Herschel’s mirror polisher, on display in the Science Museum, London. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ William_Herschel#/media/ File:William_ Herschel%27s_Mirrorpolisher.jpg)

recording what William observed at the telescope, and in time she would establish herself as a first-class observer and telescope maker in her own right. William Herschel’s first excursion into telescope making came in 1773, when he experimented with the construction of relatively small, singlet refractors (small in aperture, but certainly not in focal length – one of them being 30 feet long!). He soon grew tired of their unwieldiness and so-so optical quality, though, and soon turned his attention toward reflectors that promised much greater aperture and compactness. These were not the familiar telescope mirrors of today, however, as silver-­ on-­glass optics would not make their appearance until long after Herschel’s death. Instead, they were fashioned from speculum metal, which, as we saw in a previous chapter, was a brittle and hard alloy composed mainly of copper and tin. At first Herschel made several mirrors for a 5.5-foot focus Gregorian reflector but soon turned to the simpler Newtonian design. All of his telescopes from that point on were long-focus Newtonians of ever-increasing size, culminating in the great 40-foot reflector, which we shall discuss in more detail later in the chapter. In the summer of 1774, William and Caroline moved to more spacious lodgings at 19 New King Street, Bath. This house had more room for telescope making, a roof for observing and even a grass plot that could support a large telescope. Very soon, the house was turned upside down as William churned out numerous mountings and speculum mirrors with focal lengths as large as 20 feet (Fig. 8.3). He soon produced a 7-foot telescope (as previously mentioned, telescopes in Herschel’s day were specified by their focal length rather than by the size of their optics), probably of around 6-inch aperture. He also made several 9-inch mirrors for a 10-foot reflector (and much later a 10-foot reflector with a 24-inch mirror), ­followed by 20-foot models having 12- and 18.7-inch mirrors as described below. But his favorite early reflector was another 7-foot that contained “a most capital speculum” as he described it, of 6.3-inch aperture. This was the telescope that he

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used for his first “review” of the heavens and the one with which he discovered the planet Uranus. He put his back into this work. In her memoirs, Caroline Herschel later related some intriguing glimpses of her brother’s preoccupation with his astronomical work: But every leisure moment was eagerly snatched at for resuming some work which was in progress, without taking time for changing dress, and many a lace ruffle was torn or bespattered by molten pitch, etc., besides the danger to which he continually exposed himself by the uncommon precipitancy which accompanied all his actions….For my time was so much taken up with copying music and practising, and besides attendance on my brother when polishing, since, by way of keeping him alive, I was constantly obliged to feed him by putting the victuals by bits into his mouth. This was once the case when, in order to finish a seven foot mirror, he had not taken his hands from it for sixteen hours together. In general he was never unemployed at meals, but was always at those times contriving or making drawings of whatever came in his mind.

Herschel’s study of Smith’s Opticks instilled in him the keen desire to examine the wonders of the heavens for himself, and it was this book that became his guide in his telescope-making enterprise. In addition to what he learned from books, Herschel received some tips from an amateur living in Bath who had tired of the hobby and who willingly sold his stock of optical tools and half-finished mirrors to the young enthusiast. Makers of reflecting telescopes, as we saw in an earlier chapter, had always been faced with the problem of deciding upon the composition of the metallic alloy. The polished surface of the mirror must be brilliantly reflective, non-porous and, ideally, slow to tarnish. In addition, the metal should be easy to work, being not too brittle, nor too sensitive to changes in temperature, which would result in a distortion of the images served up. Copper, tin, silver, antimony and arsenic, in various proportions, were all considered. For his own work, Herschel found by his own experimentation that the best all-around metal for his speculum mirrors should be made with copper and tin in the ratio 12:5. It was Herschel’s practice to cast his specula in molds of loam baked by burning charcoal, and, ever resourceful, in one instance the mold was fashioned from pounded horse dung! (Fig. 8.4) With much trial and improvement, the general procedure Herschel gravitated towards in the construction of his mirrors was broadly as follows. He first extricated circular brass gauges to the rough curvature prescribed for the speculum and this in turn was used to create a sand mold into which was poured the molten speculum metal. Following this, the labor-intensive process of grinding, polishing and casting the mirror could begin until it was imparted with the intended spherical or parabolic figure. Herschel employed various procedures for converting the rough casting into a perfect mirror, which involved the use of an accurately shaped ‘tool,’ as well as various abrasive and polishing materials. He adopted an effective polishing stroke, by which the tool was applied to the casting in a to-and-fro motion across the diameter of the mirror, or in circular sweeps around its center. After a few years of casual observing with his homemade telescopes, Herschel grew disillusioned by this kind of desultory work and longed to embark on a study of the outstanding astronomical problems of his day. How far were the stars? What

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Fig. 8.4  Replica in the William Herschel Museum, Bath, of a telescope similar to that with which Herschel discovered Uranus. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ William_Herschel#/media/ File:HerschelTelescope. jpg)

was the nature of the stellar bodies and the Sun? What was the nature of the mysterious nebulae? Are double and multiple stars physically associated with each other or is their close association a mere chance optical alignment? What is the Milky Way and where does the Sun and its retinue of worlds reside within it? Herschel’s earliest observations of the heavens formed the basis of three successive reviews, each of which involved a progressive improvement in the power of the telescope employed as well as a corresponding extension of scope so as to include progressively fainter stars in each survey. Most of the objects Herschel discovered in his first review of the heavens were made with his prized 7-foot focus Newtonian – with an aperture of just 6.3 inches – and were double and multiple stars, but he also found a number of his early clusters and nebulae with an instrument of essentially the same size. A few months after the commencement of his second review of the heavens, which began in the late summer of 1779, Herschel was observing the Moon late one December evening with an 8-foot telescope of his own construction, which he had set up on the street in front of his house. A curious passerby stopped and sought Herschel’s permission to look through the telescope, which he enthusiastically granted. Little did he know that the same gentleman was a one William Watson, son of the celebrated Dr. William Watson, distinguished physician and pioneer in elec-

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tricity. Both he and his father were already Fellows of the Royal Society and both were later knighted for their scientific work. Watson was so impressed by the quality of the images Herschel’s telescope served up that he promptly invited its maker to join the newly formed but shortlived Philosophical Society of Bath, where he was asked to read his scientific papers to an audience of 30 or so other members. Watson rendered Herschel an important service in passing on to the Royal Society several of his astronomical papers. In this way, Herschel’s early astronomical work was disseminated to an ever-increasing circle of scientists, adding to his notoriety among distinguished men of English science. It was during the course of his second review of the heavens, carried out with a reflecting telescope of 7 feet in focal length, that Herschel, on the night of March 13, 1781, made the discovery that would launch him to international fame, a discovery unprecedented in recorded human history, nothing less than the detection of a new major planet of our Solar System. This was the event that neatly divided the astronomer’s life into two nearly equal parts, which marked the closing of his years of struggle and relative obscurity and the beginning of his career as an international figure in the world of science. For his discovery of the new planet, which in due course received the name Uranus, the Royal Society in November 1781 gave Herschel its Copley Medal, and the following month he was elected a fellow of the society. In April 1782 Herschel was informed that King George III had expressed a wish to see him, and, having made out a list of double stars that could be shown to advantage, he packed his 7-foot telescope and traveled to London late in May. There he was given hospitality by the elder William Watson, who had his residence in Lincoln’s Inn Fields. A few days later Herschel was graciously received by the king, who directed that the telescope should be sent to Greenwich. There the instrument would remain for a month, during which time the Astronomer Royal and other experts made trial of it, declaring that in definition and in magnifying power it excelled all other telescopes they had ever looked through! The instrument was then transported to Windsor where, on July 2, Herschel showed the planets Jupiter and Saturn and other celestial objects to the king and queen and their family. With a little prompting from the younger Watson, Herschel was induced to apply to the king for the means of devoting himself wholly to astronomy. It was soon arranged that he should give up his musical profession and settle somewhere in the neighborhood of Windsor, where he would receive a salary of £200 a year with only the obligation of occasional attendance upon the royal family to show them celestial objects of interest through the telescope. The king subsequently made an allowance of £50 per year to Caroline Herschel, as her brother’s assistant. And, as we shall see, the British sovereign authorized substantial grants for the construction and maintenance of the great 40-foot telescope. So it was on August 2, 1782, that Caroline and William moved into their new premises at Datchet, about a mile and a half from Windsor Castle. In the garden the astronomer erected his favorite telescope, a 20-foot reflector. From now on, for many years, so as not to miss a single hour of possible observing time, he would watch through the night for a clear spell, or post a watchman to do so. His daylight

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Fig. 8.5  Schematic of Sir William Herschel’s 40-foot (12-m) telescope. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/William_Herschel#/media/File:Lossy-page1-3705pxHerschel%27s_Grand_Forty_feet_Reflecting_Telescopes_RMG_F8607_(cropped).jpg)

hours were devoted to telescope making in his workshop. It was during the 3 years spent at Datchet that Herschel published his earliest papers on the two principal themes of his lifelong research in astronomy – the free motion through space of the Sun and its planetary family, and the structure of the system of stars of which the Sun is a member. However, the Datchet house suffered from a drawback that the surrounding land was flooded whenever the Thames overflowed its banks; and after suffering a severe anxiety attack, Herschel decided to move to Clay Hall in Old Windsor in the summer of 1785. But the landlady there proved to be a bit of a tyrant, and the Herschels departed within a year. They finally settled at Slough in the house on Windsor Road, which stood until recently as the home of the great astronomer’s descendants and the repository of his relics. Here Hershel resumed his observations on April 3, 1786, and here he was to spend the rest of his days (Fig. 8.5). Herschel’s telescopes far surpassed in both quality and size any other telescope in the world at that time. After comparison trials at a number of observatories in

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England including Greenwich, he stated with confidence, “I can now say that I absolutely have the best telescopes that were ever made.” His fame as a telescope maker spread rapidly and soon he was flooded with requests from other observers and observatory directors to make instruments for them. Although he was not in the telescope-making business as such, his allowance from the king – while freeing him from his musical duties – did not entirely meet his expenses, and so he began to make and sell telescopes privately. In addition to at least 60 complete instruments (most of them 7- and 10-feet in size), he also made to order several hundred mirrors in addition to those he employed for his own surveys! It is frequently stated that a modern 6- to 8-inch telescope will show a large percentage of the objects in the Herschel catalog (including many of his faint and very faint nebulae), and that a good 12-inch telescope should reveal every one of them, even though most were found using his two 20-foot instruments. This was made possible due to the much higher reflectivity of today’s coated-glass telescope mirrors – and to a lesser extent to modern eyepieces as well. Curiously, Herschel primarily used single-lens oculars; multiple-element designs and antireflection coatings only appearing far in the future. The author fully agrees with this assessment based on years of viewing these wonders with telescopes ranging from 2 to 12 inches in aperture. Herschel’s two “workhorse” telescopes – those used for all his future reviews of the heavens – were his 20-foot reflectors. The earlier and smaller of these in terms of aperture (referred to as the “Small 20-Foot”) used 12-inch mirrors, while the larger and later instrument (called the “Large 20-Foot”) employed 18.7-inch mirrors. Note that “mirrors” is plural, since several were needed for each telescope – the one that was currently in use, and at least one  other in the process of being repolished and refigured due to the rapidity with which speculum metal tarnished! The telescope with the 18.7-inch mirrors became his most useful telescope, and in later years he even preferred it to the massive 40-foot instrument, for it was both much easier to use and was found to be superior optically. The 20-foot telescope was in constant use on clear nights from dusk to dawn, revealing over 2,000 previously unknown star clusters and nebulae. Due to the substantial light loss at each reflected surface, Herschel eventually decided to dispense with the secondary mirror in the Newtonian form. Instead, he tilted the primary mirror so that its focus could be examined off-axis directly at the front of the tube – a form he referred to as the “front-view.” This concept is still used in some amateur-­ made as well as commercial telescopes today, but instead of being called the “front-view” form it is now known as the “Herschelian” in honor of its inventor. And while loss of reflectivity is not the concern today it was in his time, moving the secondary mirror and its support out of the optical path essentially gives the unobstructed performance more akin to a refractor but at the cost of introducing other aberrations to the optical train, especially when used on high-resolution targets (Fig. 8.6). Herschel’s most ambitious telescope-making project – indeed, the most ambitious in history up to that time – was the construction of his great 40-foot reflector with its 48-inch (or 4-foot) diameter mirror (resulting in a focal ratio of f/10).

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Fig. 8.6  Light path of the Herschelian reflector. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/Reflecting_telescope#/media/File:Herschel-Lomonosov_reflecting_telescope. svg)

Herschel actually cast several mirrors for it before he finally was able to get one that would take an acceptable polish and figure. (Interestingly, Herschel had much earlier tried to make a mirror for a proposed 30-foot telescope, but gave up on the idea after several near-disastrous events that occurred during attempts at casting it.) In 1787, Herschel climbed into the mouth of the huge tube and searched for the focus using one of his first mirrors. His target was the Orion Nebula, which he described as “extremely bright,” but the figure was far from perfect. On later attempts he used Saturn as his test object, discovering several new satellites in the process. Some idea of the light grasp of this instrument can be had from this famous description by Sir William of the star Sirius as seen through it, “the appearance of Sirius announced itself…and came on by degrees, increasing in brightness, till this brilliant star at last entered the field of view of the telescope, with all the splendour of the rising sun, and forced me to take the eye from that beautiful sight.” Regular work with the telescope finally began in 1789. But Herschel was never pleased with the telescope’s performance. Perhaps this is best summed up in the following lines from telescope historian Henry King’s definitive work, The History of the Telescope: The paucity and irregularity of Herschel’s observations with the 40-foot leave little doubt that the great telescope failed to meet its maker’s expectations. In the first place, the weather was seldom good enough to allow full use of its aperture and, when conditions were favorable, Herschel preferred the smaller and more manageable 20-foot. He found there were few objects visible in the 40-foot which he could not see in its smaller counterpart.

That very few of the objects contained in the Herschel catalog were actually discovered with the 40-foot certainly affirms King’s conclusion. How very sad for Herschel after all his labors over this great instrument! But while it was a disappointment for him, it was certainly not so for the many sightseers who came to gawk at this wonder of the ages, including members of the royal family and other dignitaries of all levels, as well as noted scientists the world over. One famous early episode from this period includes the day the king came to inspect the telescope while still under construction, bringing with him the Archbishop of Canterbury. As they were about to enter the open mouth of the tube (which at this point still lay on the ground), the king said “Come, my Lord Bishop, I will show you

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the way to Heaven!” Even today, the image of Herschel’s mammoth 40-foot telescope remains one of the great – if not the greatest – icons of astronomical history. In closing, two very important points need mention. First, all of Herschel’s many telescopes were mounted as simple altazimuths, being moved about the sky and tracked manually. And second, they were all mounted outside of his various residences in the open night air. For all his fame and discoveries, Sir William never had an observatory! In his efforts to perfect the reflecting telescope Herschel bestowed more labor and expended more wealth than had probably ever been lavished before upon the development of any scientific instrument; and he acquired extensive experience in its use under all kinds of atmospheric conditions. In so doing, Herschel established the reflector as a fundamental instrument of modern astronomy. Herschel also learned to distinguish between the several different functions which a telescope can perform, revealing stars invisible to the unaided eye, magnifying extended objects, and resolving close stellar pairs or clusters into separate images. And he clearly understood how these various capacities of a telescope depend upon the relevant optical dimensions of the instrument. Herschel also stumbled upon and clearly described some of the small-scale optical phenomena of disks and fringes that we now associate with the fundamentals of the wave theory of light but of which the imperfect knowledge of his day could scarcely explain. He was also fertile in the invention of optical adjuncts to the telescope, notably micrometers, and his technique for grinding and polishing short-­ focus lenses enabled him to employ magnifications of such powers as his contemporaries found barely credible. During his 36 years at Slough, Herschel returned to the problems of the solar motion and the structure of the stellar system. He was also became intensely interested in the theory of telescopic observations, the constitution of the Sun and the physics of solar radiation, planetary and cometary studies, the phenomenon of variable, nebulous and double stars, the classification of stars according to their brightness, the cataloging of nebulae and star clusters discovered while sweeping the heavens, and theories of the evolution of celestial systems. Papers on these seminal topics followed one after the other in no particular order, and we shall try to explain their contents systematically later in the chapter. The sale of telescopes from Herschel’s workshop became a lucrative business; many of them distributed all over Britain and the Continent, substantially increasing his personal wealth. It may seem a matter for regret that Herschel’s time and energy should have been taxed in this manner, and to so little purpose, for we hear of no seminal discoveries made by the king of Spain or by other recipients of these wondrous optical accoutrements. His best-selling instrument was the 7-foot reflector, one of which was purchased by Hieronymus Schröter for the princely sum of £65. However, this trade obliged Herschel to maintain a staff of mechanics to carry out the rough work to which he had only to make the finishing touches. Much of this new source of capital was expended on ‘expensive experiments,’ as he put it, of which 2,160 are recorded, on polishing mirrors by machinery.

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Fig. 8.7 Caroline Herschel (1750–1848), one of the greatest female astronomers of all time. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Caroline_Herschel#/media/ File:ETH-BIB-Herschel,_ Caroline_ (1750-1848)-PortraitPortr_11026-092-SF.jpg)

Herschel was occasionally assisted in his manufacture of telescopes by his brother, Alexander. Although not the eldest son, William early adopted something of a guardian’s role towards his rather unstable siblings, particularly Alexander and Dietrich, both of whom were brilliant musicians. After his father’s death, Alexander joined his brother William in England, where he remained for nearly 50 years, passing his time between the orchestras of Bath and the workshops at Slough. In 1816 Alexander suffered a nervous breakdown and decided to join Dietrich at Hanover, with William making provision for him until his death in 1821. Dietrich, the youngest brother, was allegedly of a mercurial disposition. For example, in 1777 William left his workshop in pursuit of him, after learning that he had intended to run away to the East Indies. In 1807 Dietrich, by now broken and embittered by a further occupation of Hanover, left his family and came to England to seek a livelihood, remaining there for nearly 40 years (Fig. 8.7). In the summer of 1786, soon after he had settled at Slough, Herschel made what proved to be his final visit to Germany, taking with him one of his 10-foot reflectors as a gift from King George III to the University of Gottingen, when he saw his mother for the last time. At her brother’s suggestion, Caroline Herschel had taken up comet hunting on her own account, and during his two-month absence in Germany she discovered her first comet. She was equipped with a small reflecting telescope having the wide field view suited to its purpose, her observing station

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being a flat roof of a small detached building used as a library and as her private apartment, and later known as the ‘Cottage.’ Although her own career as an observer was increasingly sacrificed to her brother’s more illustrious researches, between 1786 and 1797 she managed to discover eight new comets in all, as well as many previously unknown nebulae not yet cataloged. Two years after the settlement at Slough (which became known as Telescope House) on May 8, 1788, William married Mrs. Mary Pitt (nee Baldwin), widow of John Pitt of Upton, in the parish to which the Herschels belonged. They had one child, John Frederick William, born on March 7, 1792. Herschel’s bride brought him a considerable fortune in her own right. But the marriage marked somewhat of a crisis in the dedicated life of Caroline Herschel. For close upon 16 years she had kept house for her brother and, in her devotion to him, had abandoned a promising musical career for her brother’s astronomical causes. But now, at the age of 38, she was obliged in the natural order of things to give place to a younger family member. Although she continued as her brother’s assistant she felt obliged to seek her own privacy. Caroline’s journals for this period, in which her innermost feelings were recorded, were later disposed of. However, she eventually established friendly relations with her sister-in-law, and her affections grew rapidly for her nephew, John Herschel, watching his genius unfold as he matured to manhood, and were transformed into pride when his scientific achievements, second only to his father’s, were acclaimed the world over. Throughout his career, Herschel enjoyed the respect and regard of the leading astronomers of his day, and much of his correspondence with them were carefully preserved in his diaries. With a small band of his contemporaries he formed early but enduring ties of friendship, particularly with the younger Watson, who first made his work known to the Royal Society. Herschel’s election to the Society brought him into touch with its president, Sir John Banks, naturalist and explorer, who had come to occupy a commanding position in the annals of British science comparable to that once held by Newton. One of the Bank’s staunchest supporters was Charles Blagden, an army man and inveterate traveler, who became a secretary of the society in 1784. Indeed, it was to him that Caroline wrote in 1786 to report the discovery of her first comet, her brother being in Germany at the time. Other friends were Alexander Aubert, London businessman and astronomer, who cordially received the Herschels at his well-equipped private observatory near Deptford; and Patrick Wilson, Professor of Astronomy at Glasgow, who, after retirement, came with his sister on a visit to Telescope House, where he conducted a series of solar observations. Another highly placed friend and well-wisher of Herschel was the Astronomer Royal, Nevil Maskelyne, from whom he often received timely and precise information as to the whereabouts of newly discovered celestial objects, and who first guessed the true planetary status of Uranus. Herschel’s foreign correspondents included J.  H Schröter, a lawyer and amateur astronomer of Bremen, who spent many years studying the surface features of the Moon and the planets with a 7-foot reflector of Herschel’s construction and who subsequently came to be called the

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“Herschel of Germany.” Their friendship was undisturbed by Herschel’s good-­ natured banter at Schröter’s claim to have observed mountain ranges on the planet Venus more than six times the height of Chimboroza, but of which the Slough telescopes revealed no trace! Another correspondent was the French astronomer, Jerome Lalande (1732–1807), who visited Herschel in 1788 and continued to correspond with him as the opportunities arose, even after the outbreak of the Revolutionary War. In his later years, Herschel increasingly indulged in his taste for travel as a temporary escape from his round-the-clock scientific duties. In 1792, the year of his son’s birth, he made two extensive tours through England and Scotland in the company of his friend General John Komarzewski, a cultured Polish nobleman, who, together with William Watson, stood as godfather to the boy. Invariably, Herschel and his learned friends seemed to have concentrated their attention chiefly upon industrial developments in the regions through which he passed. At Birmingham, for example, they were the guests of James Watt, the celebrated developer of the steam engine, and Herschel returned to Telescope House with his notebooks crammed with sketches of the new machines that were transforming Britain from an agrarian economy into an industrial powerhouse of the world. At Glasgow University Herschel was conferred with the degree of Doctor of Laws, and during his visits to Edinburgh he made the acquaintance of the distinguished chemist, Joseph Black. In the summer of 1802, Herschel, accompanied by his wife and 10-year-old son, visited Paris, where he met several of the leading Frenchmen of science, among them the astronomers Laplace, Delambre and Messier. He was also received by the First Consul, Napoleon Bonaparte. In the winter of 1808 Herschel suffered from a severe nervous condition from which he never completely recovered. To these last years of his life, however, belong some of his boldest searchings into the origins of stars and their aggregation into clusters and his final attempt to estimate the dimensions of the galaxy. A tour in the summer of 1809 took the Herschels off to the Lake District, and on the way back to Slough they called at Cambridge. Here, Mrs. Herschel introduced her son to  the administrators of St. John’s College, where he was soon to enter as an undergraduate, living in the lodgings with his mother to keep house for him. In 1810, the family journeyed to Scotland, calling once again at Birmingham to see James Watt, and in later years they made further extended tours. In 1813 John Herschel graduated as Senior Wrangler and was proposed by his father for the fellowship of the Royal Society, though not yet of age. After casting about for a profession, John became his father’s assistant in 1816 (Fig. 8.8). Herschel was a member of many European societies, and he was knighted by the Prince Regent in 1816. In old age he became president of the Royal Astronomical Society. Herschel only consented to be elected President on the understanding that he should not be expected to take any active part in the work of the society. Indeed, Herschel never attended any of the society’s meetings, but his last paper, a final installment of his catalog of double stars, was published in the first volume of its Memoirs. Throughout his life, Herschel was not particularly worldly, and appears to have been incapable of cynicism. In his mature years, he seems to have adopted a reli-

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Fig. 8.8  Sir John Herschel (1792–1871) in the autumn of his life. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ John_Herschel#/media/ File:Julia_Margaret_ Cameron_-_John_ Herschel_(Metropolitan_ Museum_of_Art_copy,_ restored)_levels.jpg)

gious position widely shared by educated men of his day and in harmony with the prevailing temperament of the Church of England. He believed that the universe was fashioned by a Divine Creator, whose power and wisdom are made more abundantly evident by the scientist, whose duty was to unveil the operation of nature. William Herschel died peacefully at his home in Slough on August 25, 1822, in his eighty-fourth year. He was buried at Upton in the Church of St. Lawrence. A stone tablet under the tower marks the spot and bears a Latin inscription on which are recorded the words so often quoted in tribute to the great astronomer: Caelorum Perrupit Claustra (he broke though the barriers of heaven). We shall now take a closer look at some of the astronomical science generated by Sir William Herschel during his long and productive career. Five days after he deployed his large 20-foot reflector, Herschel began a systematic sweep of the heavens with it. For his sweeps he usually used a magnification of 157×, which offered a small 15′ (about half a full Moon diameter) field of view. The eyepiece was mounted on the upper side of the telescope’s octagonal tube, where it made a 45-degree angle with the vertical when the telescope was horizontal. Herschel preferred this observing position, looking down as if at a reading desk, and used this arrangement until September 22, 1788, in Sweep 600, when he changed to the ‘front view,’ as he called it. By removing the small diagonal mirror and placing

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the eyepiece at the front end of the tube, he found the images to be just as good and well defined as at the Newtonian focus and the light “incomparably more brilliant.” Evidently he found this position very convenient. Before starting a sweep, Herschel pointed the telescope toward the meridian and observed from a 9-foot long movable gallery. The telescope hung freely in the center of the mount, and the observer moved it with a handle fastened near the eyepiece. Drawing the telescope along by hand in a lateral motion, Herschel would walk backward and forward along the gallery. This allowed him to make slow oscillations 12–14° in breadth, each taking generally 4–5 min to complete. At the end of each oscillation he took short notes on what he had seen. If he had found a new nebula or star cluster, he carefully noted the stars in the field of view of both the finder ‘scope and the main telescope so as to enable him  to locate the object again. After this procedure, Herschel would then raise or lower the instrument about 8 or 10 arc minutes along a north-south line and then perform another oscillation. He then continued for 10, 20 or 30 oscillations according to the circumstances, and the whole sweep was numbered and registered in his journal. At first Herschel took his own notes, but after 41 sweeps the disadvantages of doing so became obvious. Because he needed light to write, his eye could never achieve the dark adaptation required for his “delicate observations.” In Herschel’s day, there was little knowledge of the benefits of keeping one’s eyes dark adapted. Indeed, it is a wonder to some modern scholars that he could see so much given that he had to frequently use lamps to record his various observations. Furthermore, the gallery was not well placed, and holding down the heavy telescope at the ends of the oscillations, when it tended to arch upward, led him to become easily fatigued. So Herschel began to sweep by elevating and lowering the telescope manually with a vertical motion, employing a small bell to signal to his assistants to move the telescope to another field. Caroline wrote down his observations, repeating everything back to him so that he could verify “the picture before me” while preserving his night vision. A few sweeps (42–45) were done experimentally, and with Sweep 46 on December 18, 1783, Herschel’s long survey of the heavens commenced. This series was not closed until September 30, 1802, with Sweep No 112. Each object’s description and position relative to the nearest Flamsteed star was copied on single sheets of foolscap. A great deal of effort was made to obtain accurate coordinates, and Herschel experimented with various techniques, such as using an assortment of pulleys, knotted ropes, bells and iron plates to tell him where he was in the heavens. Eventually, there were a total of 2,508 new objects recorded. Caroline also had a similar set of sheets for Messier’s nebulae and clusters. We now know that she was very careful and accurate and made only two or three positional mistakes of 1° in all of her entries – and these she made in old age. All in all, a total of seven Sweep Books were eventually presented to the Royal Society. As we have seen, it was in 1785 that Herschel petitioned the king for a large instrument with a 30- or 40-foot focal length. The king chose the 40-foot option and granted £2,000 toward its construction, and in September of the same year work commenced. The telescope, its massive mount and its mirror all were designed exclusively by William. The first of its two functioning mirrors was cast in London;

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it spanned 49.5 inches in diameter and was 2.5 inches thick. Ten men polished it, giving the speculum “a very white surface.” The mirror was very brittle, however, and came out of the mold thinner than intended. The resulting weakness would never permit it to give a good image, and the mirror eventually was discarded. However, first light for the 40-foot telescope was achieved with this mirror on the evening of February 19, 1787, when Herschel crawled inside the tube and hand-held the eyepiece to find the focal point. The view of the “Lucid Spot” in Orion was far from perfect, but it was better than expected and extremely bright. So the Herschels immediately began trying to refine the mirror. In August 1787, King George granted Herschel yet another £2,000. A second mirror cracked during the casting process, but in February 1788, a third mirror was successfully cast. This mirror weighed a whopping 2,118 pounds, had a diameter of 48 inches and was 3.5 inches thick throughout. An iron ring surrounded the mirror, and an iron cross supported it from behind. The mirror was successfully polished by machine. The telescope’s optical tube was 39 feet, 4 inches long, with a diameter of 4 feet 10 inches. Herschel did not deem the Great Telescope completed until August 28, 1789, though – the same night that he discovered the sixth satellite of Saturn (Enceladus) with it. However, this turned out to be a re-discovery, as Herschel had actually observed the satellite 2 years earlier with the 20-foot reflector but did realize its significance at the time. Herschel observed with the 40-foot at the “front view” from an enclosed adjustable seat that was mounted on the lower side of the tube’s front end. With no secondary mirror, the primary mirror’s focal point was placed 4 inches above the lower side of the tube’s front end. This meant that the observer’s head would not block incoming light. A “slider” with an adjustable base was located at the lower end of the tube, where it pointed directly at the center of the great mirror. It carried a brass tube, into which eyepieces of various focal lengths or micrometers were inserted. Due to its massive size, however, Herschel seldom used the Great Telescope, even though it was his most celebrated instrument (and at the time, the world’s largest). The telescope took a considerable amount of time to ready for use and required two workmen to move. Because of its weight, the mirror had to be left inside the telescope, so it tarnished quickly. By contrast, Herschel’s two 18.75-inch mirrors remained highly polished, as they were stored in protective boxes and placed in their telescope tube only when observations were about to be made. Herschel used the 40-foot reflector sparingly and wrote that it should be used only to examine objects that other instruments could not reach. Interestingly, Herschel never reported seeing spiral structure in any nebula through the 40-foot telescope, even though such structures in some galaxies should have been obvious with so large an instrument. Equally strange is that Herschel did not distinctly mention the fifth or sixth stars of the Trapezium in M42, an object that he had observed repeatedly. On one occasion, the gigantic telescope even failed to show Saturn’s rings! Obviously, it gave poor images, even with the second mirror. Like any of his contemporaries, Herschel observed the Moon, and, among other tasks, he carefully measured shadows cast upon its surface by its mountains. He deduced a lunar diameter of 2,180  miles, surprisingly close to today’s accurate

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value of 2,160 miles, but he also made some very controversial lunar observations. On May 28, 1776, for example, he used a 10-foot reflector at 240× to view what he believed were forests in Mare Humorum, replete with shadows cast by trees at the edge of the woods. The next night he could not see any ‘woods’ and seemed to have dropped the idea completely. However, in a 1780 letter to Maskelyne he wrote of his absolute certainty of the Moon being inhabited, and if given the chance, Herschel vowed: I would not hesitate a moment to fix upon the Moon for my habitation. What a glorious view of the heavens from the Moon. Do not all the elements seem at war when we compare the Earth with the Moon! Air, water, fire, clouds, tempests, volcanoes, all these are either not on the Moon or at least in much greater subjection than here.

In 1783 and again in 1787, Herschel reported a volcano in the Earth-lit part of the new Moon, inside the crater Aristarchus, stating that it resembled a red, 4th magnitude star. However, when other astronomers in Paris observed the same region they revealed no such apparition, and the whole issue was quietly dropped. Herschel’s observations of Mars include many references to “luminous spots” (ice caps) that appeared to project beyond the edge of the planet’s disk. He deduced that the polar spots were frozen, covered with mountains of ice and snow that melted only partway when alternately exposed to the Sun. He also noted dark spots on the surface and determined a rotation period of 24 h, 37 min and 26.3 s – very close to the modern value. Herschel was also aware that Mars had an atmosphere, noting an observation by Cassini that “a star in the water of Aquarius, at a distance of six minutes from the disk of Mars, became so faint before its occultation, that it could not be seen by the naked eye, nor with a 3-foot telescope.” To Herschel, Cassini’s observation indicated that Mars had “a considerable but moderate atmosphere” and “its inhabitants probably enjoy a situation in many respects similar to ours.” Herschel’s observations of Jupiter were focused mainly on the Galilean satellites. He noted considerable changes in their brightness and correctly reasoned that they have unequally tinted regions. As the moons rotated, he suspected, they would not present us with a constant quantity of reflected light. “The satellites have a rotatory motion upon their axes, of the same duration with their periodical revolutions about the primary planet,” he wrote. In this he was correct. Because the Galilean satellites are tidally locked they exhibit rotation periods approximately equal to their orbital periods about the giant planet. Saturn particularly interested Herschel, and he was known to follow it continually for up to 6 h at a time. This dedication led to his discoveries of the two Saturnian satellites mentioned previously. He also observed that the Encke division upon the A ring is not in the idle of that ring’s breadth, and (meaning unclear here) noted: “That this black belt is not the shadow of a chain of mountains (which some astronomers believed) may be gathered from its being visible all around on the ring. It is evident that this black zone is contained between two concentric circles.” When Saturn’s rings turned edgewise, Herschel correctly noted that they were thinner than the disks of its satellites. He also noted that the planet’s poles were flattened, like those of Jupiter, and that its atmosphere was dense. Finally he noted the

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ring planet’s rotation rate and that its rings rotated as well. On January 11, 1787, Herschel continued his observations of ‘Georgium Sidus,’ pointing out the position of some very faint stars near the planet. On the next night, two of these stars were missing. By February 5, after a half dozen more observations, he knew he had discovered a new satellite of Uranus. Before making the announcement, however, he wanted to verify that it moved. So, on the evening of February 7, Herschel kept the satellite in view for a total of 9 h, watching “this planet faithfully attend its primary planet.” He called this new satellite Oberon. During these studies he also discovered a second satellite, which he named Titania. Herschel was also in the practice of employing very high magnifications by modern standards: “When you want to practice seeing, apply a power something higher than what you can see well with and go on increasing it after you have used it some time. These practices I have acquired and I can now see with powers that I used to reject for a long time.” To search for satellites around Uranus, he would sometimes use a magnification of up to 7,200× and a ‘field bar’ to occlude the planet! Both his satellite discoveries, however, were made at the relatively low magnification of 157×, the satellites being “very nearly the dimmest objects that can be seen.” From observations made in 1787 and 1792, Herschel discovered that very “small” (faint) stars dimmed when they approached Uranus, and that the satellites became regularly invisible when they arrived at certain distances from the planet. He did not realize he was detecting evidence of Uranus’ ring system, which would not be recognized for another two centuries. Herschel also kept the planet Venus under observation for many years. He was keen to discover whether it was rotating on its axis like Earth, and if so, what its period of rotation – its day – might be. The obvious procedure was to select some mark upon the planet’s surface and to measure the time required for it to be carried right around the planet and back to its starting point. This could fix the period approximately. A comparison of observations of the planet made at widely separated times would then serve to determine this value with sufficient precision. Despite occasional impressions of transient markings on Venus, Herschel was soon forced to conclude that the planet was enveloped in a dense cloud-laden atmosphere hiding its surface features so completely as to make determinations of its period of rotation well-nigh impossible. Towards the end of the 18th century it was well established that the distances of the planets from the Sun increased very nearly according to a rather simple numerical rule. Specifically, they were roughly proportional to the successive terms of a mathematical series known as the Titius Bode law, which states that the position of the planets can be approximated by the expression:



a = 0.4 + 0.3 × 2 m , where a is the distance in astronomical units, and m = minus infinity, 0,1, 2 etc.

For Mercury, m = minus infinity, for Venus, m = 0, for Earth m = 1 and for Mars, m = 2, etc.

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However, the scheme had a notable flaw; there was one term (m = 3) of the series to which no known planet corresponded. This deficiency was reflected in the disproportionately wide gap between Mars and Jupiter, and a group of astronomers banded themselves together to search for the planet which, it was felt, ought to occupy this vacancy in the Solar System. On the first evening of the new century (January 1, 1801), an Italian astronomer, Giueseppe Piazzi (not himself a member of the search party), discovered an object of the eighth magnitude moving slowly among the stars of the constellation Taurus. It proved to be a planet revolving between the orbits of Mars and Jupiter, and it was eventually named Ceres, after the tutelary goddess of Sicily, where Piazzi had established his observatory. The object was lost for a time in the Sun, but the few observations already recorded of its movements were sufficient for the young mathematician, Carl Friedrich Gauss (1777–1855), to calculate its orbit, so that when it appeared again in the night sky astronomers knew where to look for it. It was re-discovered at the end of 1801. Early in 1802 Herschel began to search for the new planet in the region of the heavens where he believed it to be, but his efforts were unrewarded until he was informed of its exact position by the Astronomer Royal, Neville Maskelyne. He first saw the new world on February 7, 1802, but only after observing the wanderer for a week could he discern the minute disk that distinguishes a planet from a star. The disk appeared faintly ruddy, and its apparent diameter roughly one fifth that of Uranus, which suggested that this world must be very small in the scheme of things. By the time Herschel reported on his observations of Ceres, another object of the same kind had been discovered by Heinrich Olbers, a physician and amateur astronomer based at Bremen, Germany, who bestowed upon it the name of Pallas. Using his lucid-disk micrometer, Herschel tried to determine the angular diameters of these two elusive members of the Solar System, for in determining their approximate distances from Earth, he could estimate their diameters in miles. But this technique was unsuited to the difficulties of measuring such small objects, which usually appeared a little fuzzy in the telescope. There were also optical complications that he was only just beginning to understand. Herschel was uncertain whether to class Ceres and Pallas as planets or as comets. They revolved around the Sun in normal planetary orbits and in the same direction as the other planets, but their sizes were negligible by planetary standards. Indeed, their orbits were inordinately close to each other and were inclined at considerable angles to the zodiacal plane to which the other planets broadly adhered. Moreover, they showed no signs of possessing atmospheres or satellites. On the other hand, they had few of the characteristic properties of comets. Perhaps they could be likened to periodic comets returning from their great distances from the Sun. In the end Herschel decided to put Ceres and Pallas in a class by themselves. He wanted to name them after some property that particularly distinguished them, and as even in a good telescope they looked very much like stars, he called them asteroids, or ‘star-­ like bodies.’ Writing to Herschel on June 17, 1802, Olbers suggested very tentatively that Ceres and Pallas might be two fragments of a planet formerly occupying an orbit between Mars and Jupiter but had become disrupted, perhaps millions of years ago,

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by an internal explosion or by a collision with a comet. This would explain why the two little planets varied in brightness from night to night, as irregularly shaped rotating masses ought to reflect a varying amount of sunlight. Herschel thought it probable that further asteroids would be discovered in the course of time, and so he was not especially surprised when in 1804 the German astronomer K. L. Harding detected yet another member of this class, which, in due course, received the name of Juno. Once again Herschel was indebted to Nevil Maskelyne for information that enabled him to pinpoint the star-like object in the heavens and to classify it confidently along with Ceres and Pallas. It showed no real disk; its angular diameter, he concluded, could not therefore amount to as much as half a second of arc. In preparing to determine, with a 10-foot reflector, the angular diameter of Mr. Harding’s ‘asteroid,’ Herschel carried out a series of experiments to determine the smallest planetary disk that could be seen with the instrument, as well as the magnification required to render its circular shape unmistakable to the eye of the observer. More generally Herschel wished to ascertain the most important factor that sets a limit to the possible measurements of this kind. Was it the aperture, the focal length or the magnification? In so doing, Herschel helped establish principles of telescopic optics we still find useful today. Herschel subjected his telescope to a series of tests on tiny spheres – pinheads fashioned from globules of silver, sealing wax, pitch and the like, of various sizes. Their dimensions and their distances from the telescope were accurately measured so that the angle they subtended at the observer’s eye was determined, and the magnification needed to make them appear as disks was noted. The smallest such angle capable of being estimated with the telescope was of the order of one- or two-tenths of a second of arc. Herschel had long been aware that a source of light, whether artificial or a star, was too small or distant to appear in the telescope as a disk in its own right. Nevertheless, it did give rise to a ‘spurious disk,’ a term still applied to this phenomenon. He also noticed that the size of this disk decreased as the magnification was increased, but that it expanded when its effective aperture was reduced by covering the outer portion of the mirror with a ring-shaped screen. On the other hand, the effect of covering the central portion of the mirror was to diminish the size of the spurious disk below what it was when the whole mirror was open. In this manner, a real planetary disk could be distinguished from a spurious one that might mask it. Spurious disks have been explained by the wave theory of light, according to which a point source produces in the telescope not a point image but a minute disk surrounded by concentric rings alternately bright and dark that rapidly attenuate with increasing distance from the central maximum. This was a forerunner of George Bidell Airy’s theory of stellar diffraction. Yet another asteroid was discovered in 1807, again by Olbers. No sooner had the news reached Herschel than he commenced his search the same evening but once again he relied on the precise information from Maskelyne to enable him to track the wanderer down. Viewed through a telescope, Vesta showed no real disk to dis-

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tinguish it from a star, nor any nebulosity, so Herschel did not hesitate to include it in the now established class of asteroidal bodies. When Herschel had conceived the idea of establishing parallax in double stars, he undertook a series of “reviews” of the heavens largely for the purpose of discovering and cataloging these objects. His earliest review was carried out with a 7-foot Newtonian telescope of 4.5 inches aperture and extended down to stars of the fourth magnitude. The second review, begun in the summer of 1779, with a 7-foot instrument of 6.2-inch aperture, extended the survey to stars down to the eighth magnitude, and it was these data that provided the body of work for Herschel’s first catalog of double stars, as well as affording occasion for his historic discovery of Uranus. The third review of the heavens, begun at the end of 1781, was undertaken with the same instrument, but, whereas he had previously used magnifications up to about 220, he now employed powers as high as 6,000! This more thorough review took in all the stars of John Flamsteed’s catalog, together with others extending at least as faint as the twelfth magnitude. In all, it embraced many thousands of stars. His work rate in these projects was prodigious even by modern standards, examining as many as 400 stars in the course of a night’s work. He sought to identify any stars included in Flamsteed’s catalog, noting their colors. The principal fruit of this operation was a second double star catalog, presented at the end of 1784. A further installment, bringing the number of doubles up to 848, proved to be Herschel’s last paper. Besides double star lists Herschel’s catalogs contain multiple groups consisting of three or more members. In listing these objects Herschel identified each by giving its designation in Flamsteed’s catalog, and he recorded the position angle (measured in angular degrees eastward of north) of the secondary relative to the primary. He also noted the comparative brightness of the two stars and their colors, which often presented striking contrasts. Herschel classified his double stars according to their degrees of separation, and he included in his catalog even pairs of stars separated by 1 or 2  min of arc, for though they were too widely separated to be suited to the investigation of annual parallax, they nonetheless could serve another purpose that he already had in mind, that of establishing the motion of the Sun and its planetary retinue through space. Such a motion might be expected to produce what Herschel called a ‘systematical parallax,’ or what is now referred to as a ‘secular parallax’ in the stars – a progressive alteration year after year in the apparent relative positions of stars at different distances from the Sun. What is more,  measurements of this secular parallax might enable the speed and direction of the Sun’s motion through space to be estimated. In measuring the double stars, Herschel acquired lots of experience of micrometers with all their imperfections. Even the finest silk thread was too coarse for setting exactly across the center of a star image, and measurements made with such threads, especially when the stellar components were in very close proximity to each other, were apt to accrue errors arising from the wave structure of light itself. For the same reason, the star images, which should ideally have been mere points of light, appeared as spurious disks with diameters that varied according to prevailing

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atmospheric circumstances. And the necessary illumination of the wires was sometimes too bright for the faint stars that it was intended to measure. To surmount these difficulties Herschel devised what he came to refer to his lamp micrometer. This was essentially an artificial double star, to be set up at a convenient height and distance facing the observer so that, as he or she observed a real double star with the right eye applied to the eyepiece of a Newtonian reflector, the two artificial point sources of light of the apparatus could be viewed and aligned until they coincided in the person’s vision with the members of the celestial pair. Dividing the actual separation of the sources by their distances from the observer provided their apparent angular separation, and by dividing this by the magnifying power of the telescope, Herschel could obtain the true angular separation of the components of the double star. The apparatus consisted of a 9-foot stand to which was attached, at an adjustable height, a semi-circular board pivoted at its center and equipped with a radial arm that could be raised or lowered by turning a long handle. A lamp was located at the center of the board and a second lamp could be moved up and down the arm on a slide by turning another handle. Each lamp shone through a pinhole to give a star-­ like point of light. Besides its application to double stars, Herschel also found his lamp micrometer useful in determining the apparent diameters of the planets, or, more questionably, the angular sizes of the stars themselves. In the first instance, he would make the separation of the pinholes just equal to the apparent diameter required; but later, applying the instrument to the planet Uranus, he hit upon the idea of substituting a single lamp shining through a circular aperture instead of the two sources, cut out of pasteboard and covered with paper so as to simulate the disk of the planet. Herschel called this instrument a lucid disk micrometer. By selecting from a graded series of apertures and shielding the light using  the right combination of white and black sheets of paper, the apparent size, luminosity and color of the planet were closely matched. In place of the shining disk, Herschel would sometimes experiment with a dark disk on a bright background, or with a luminous ring. His results assigned to Uranus a linear diameter of about four and a half times that of Earth, remarkably close to the modern accepted value. In a notable paper on stellar astronomy, which he read to the Royal Society in 1767, the clergyman turned scientist, John Michell (1724–1793), had argued that the very close association of these stellar objects were much too numerous to have arisen by chance from a random scattering of stars over the sky. The members of such a pair must in many instances constitute a physically connected system, and they must actually be situated near to each other in space and therefore at roughly the same distance from the observer. Furthermore, in a memoir Herschel received from Sir Joseph Banks sometime after reading his paper on the stellar parallax, Christian Mayer (1719–1783), a Jesuit astronomer based in Mannheim, Germany, had come to much the same conclusion. Mayer had been cataloging many double stars, primarily for the purpose of ascertaining the proper motions of bright (near) stars by reference to their faint (distant) neighbors. But he also expressed the view that the fainter member of such a pair

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might be revolving about its brighter companion, or that both move about a common center of gravity. Herschel did indeed note this suggestion in the conclusion of his first catalog on double stars, but he judged it “much too soon to form any theories of small stars revolving around large ones.” However, by 1802 Herschel had come to admit the following: “The odds are very much against the casual production of double stars….their existence must be owing to the influence of some general law of nature; now, as the mutual gravitation of bodies towards each other is quite sufficient to account for the union of two stars, we are authorized to ascribe such combinations to that principle.” In the same communication, Herschel also discussed a few of the simpler types of orbital motions that might be exhibited by the members of truly double (or binary) star systems. For about a quarter of a century Herschel patiently continued to make regular measurements of the slowly changing separations and position angles of some fifty stellar pairs. By 1803–4 he was able to prove that for the majority of stars considered, the accumulated alterations in their elements arose in all probability from orbital revolutions of the member stars under their mutual center of gravity (that is, their barycenter). If a shadow of doubt on the question still remained, it was quickly dispelled by the ongoing micrometric measurements of Wilhelm Struve at Dorpat (discussed in a later chapter). Thus, during Hershel’s lifetime, the law of Newtonian gravitational attraction that governs the motion of the planets in our Solar System also held throughout the stellar universe. As we have seen, in his early papers on parallax and double stars, Herschel referred to his use of magnifications of 6,000 and over. This claim was received somewhat incredulously by established astronomers, and William Watson urged him in his own interest to explain how these powers were estimated. This he did in a letter to Sir Joseph Banks in which he described the straightforward optical methods by which he and his friend Watson had independently determined these powers. Nevertheless, truth be told, some hesitation regarding Herschel’s claims persisted up to the dawning years of the 20th century. Then, in 1924, Dr. W. H. Steavenson, while carrying out a systematic examination of Herschel’s instruments, which were still preserved at Slough at this time, came upon a set of eyepieces fitted with very short focus lenses that matched some of those that had been the subject of dispute. Remarkably, subsequent examination by modern optical techniques fully confirmed the order of the powers which Herschel had claimed for his eyepieces. Indeed, there was one which, with his 7-foot reflector, would have provided a magnification of 7,676! Herschel used to stress that he had only gradually acquired facility in the use of such high powers – the ‘art of seeing’ as he put it – through much experience: “Many a night have I been practicing to see, and it would be strange if one did not acquire a certain dexterity by such constant practice.” Foremost among the problems that engaged Herschel’s attention throughout his career as an astronomer was that of discovering what he called ‘the Construction of the Heavens,’ the architecture of the system of stars of which the Sun is but one member. Although he nowhere mentions the name of Thomas Wright and seems not

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to have been acquainted with Wright’s book, An Original Theory or New Hypothesis of the Universe (1750), he adopted a very similar conception of the nature of the galaxy. The principle that the crowding of the stars into any region of the sky reflected the extent of the stellar system in the same direction was clearly stated in Herschel’s first classic papers on this problem, which we read to the Royal Society on June 17, 1784, where he elaborated on these ideas: It is very probable that the great stratum, called the Milky Way, is that in which the Sun is placed, though perhaps not in the very center of its thickness. We gather this from the appearance of the Galaxy, which seems to encompass the whole heavens, as it certainly must do if the Sun is within the same. For suppose a number of stars arranged between two parallel planes, independently extended every way, but at a given considerable distance from each other; and, calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars; while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded, according to the distance of the planes or number of stars contained in the thickness or sides of the stratum.

Herschel produced a diagram showing how an observer situated at the heart of a box-shaped stratum, or layer, of stars will see the stars projected upon the sky as an encircling ring. Resembling a giant ameba, the stars are more numerous and thickened at its center and thinner and more jagged at its extremities. As we have already seen, he worked with a Newtonian reflector of 20 feet focal length and nearly 19 inches in aperture. The instrument was restricted to observations in the meridian, but it served for the rough measurement of the position of any selected celestial object. Upon directing this telescope to a bright portion of the galaxy near the ­constellation Orion, Herschel found that the luminous cloud resolved into separate small stars of which, on an average, about 80 were simultaneously visible in the field of view. This kind of estimation of star density in various parts of the sky Herschel called “gaging the heavens.” It was the principal method that he adopted for determining the shape of the Milky Way and locating the Sun’s position therein. He would turn his telescope to one part of the sky after another and count the number of stars visible in the field of view at each setting of the instrument (Fig. 8.9).

Fig. 8.9  The shape of the Milky Way as deduced from star counts by William Herschel in 1785; the Solar System was assumed near the center. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/Milky_Way#/media/File:Herschel-Galaxy.png)

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From the outset, Herschel associated his speculations regarding the structure of the stellar Milky Way with the mystery of the nebulae, about which he had much more to say in his paper of 1784. In this work, his attention seems to have been directed to nebulae and star clusters cataloged by Messier in his by now famous catalog of nebulae. This catalog was presented to Herschel by his friend Alexander Aubert, who gave him a copy of 103 of these objects compiled by the French astronomer and the noted comet hunter, Charles Messier, which was published in 1783–4. Messier distinguished between nebulae and star clusters into which thousands of faint members are crowded; but Herschel found that his telescope was sufficiently powerful to reveal many of Messier’s nebulae as star clusters. And he seems to have expressed little doubt, at least at this stage in his career, that all nebulae would in time be resolved in this manner. That said, we shall see how Herschel was subsequently compelled to abandon this view, though it is to be acknowledged that his powerful telescopes revealed many previously unobserved nebulae and clusters; discoveries that numbered 466 in total by the time he read his paper. He also noticed that the nebulae, while on the one hand exhibiting the greatest variety of morphologies, showed a tendency to arrange themselves in long bands or filaments winding their way through the night sky and likened them to the strata in Earth’s crust. He also observed that nebulae tended to arrange themselves into concentrated groups in some parts of the sky, but that in other parts they were often associated with fairly bright stars interspersed with swathes of sky that were effectively starless. Herschel learned to recognize the observational features associated with the hinterland of nebulae, and would warn Caroline, on duty at the clock, that he was ‘on nebulous ground!’ In 1786 Herschel finally published a catalog of one thousand nebulae and star clusters he had discovered since 1785. In the introduction to this catalog, he described the development of the techniques he pioneered in detecting such objects and establishing their positions on the celestial sphere. For this project, Herschel employed the 20-foot Newtonian reflector that, when mounted upon its stand, could be elevated or lowered in the meridian so as to point in any direction between the horizon and the zenith. But as we have seen, it also had a limited ability to move in azimuth. Standing on a gallery near the eyepiece, Herschel would draw the nebulae from side to side along its limited arc, altering the elevation of the instrument slightly from time to time and noting the positions of any objects of interest. But the procedure was not only confusing but also very tiring, necessitating constant note taking by lamp, which rendered the eye quite insensitive to faint objects. All the while, Caroline was at her brother’s side, writing down everything he described verbally and reading those notes back to him. In his paper of 1785 On the Construction of the Heavens, Herschel gave the earliest description of a class of objects that he called planetary nebulae, owing to their resemblance to bona fide planets when viewed through the telescope. They appeared as bright, sharply defined disks, circular or slightly oval in shape, with a few even demonstrating a bright nucleus. With some hesitation, Herschel classed them as nebulae consisting of “stars that are compressed and accumulated in the highest

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degree.” He had in fact been led by his experience to regard all nebulous appearances in the heavens as ‘of a starry nature’ and distinguishable as collections of stars when viewed through a sufficiently powerful telescope. He found that he could trace a continuous sequence of appearances, ranging from obvious star groups, such as the familiar Beehive Cluster (Praesepe), through clusters which his telescopes could separate into stars with increasing difficulty (such as globular clusters), and even to milky patches that he could not properly resolve in his telescopes. That said, he never wavered in his belief that they were objects of essentially the same nature, only that they were located at immense distances from us. One of the chief goals of science is to explain naturally occurring phenomena using well established laws of nature. Herschel believed that objects change in the heveans, sometimes slowly, sometimes rapidly and that one could better explain the nature of many of the objects he viewed through his telescope in terms of these ‘evolutionary’ events. Among the most beautiful and unmistakable of telescope objects are the globular star clusters; and in the introduction to his nebular catalog of 1789, Herschel advanced the view that such a stellar conglomeration, with its characteristic condensation towards the center were the necessary products of some central force producing effects proportional to the time of its operation. Indeed Herschel likened the heavens to a “luxuriant garden” containing: ….the greatest variety of productions, in different flourishing beds, and to continue the simile I have borrowed from the vegetable kingdom, it is almost the same thing, whether we live successively to witness the germination, blooming, foliage fecundity, fading, withering, and corruption of a plant, or whether a vast number of specimens, selected from every stage through which the plant passes in the course of its existence, be brought at once to our view.

Herschel attempted to classify the way in which stars are found associated with their nebulosity, and, secondly, the various types of star clusters from the most irregular up to the wonderfully symmetric globular aggregations into which he believed the Milky Way was destined eventually to resolve itself. His intention was to find additional evidence of the formation of stars by the condensation or absorption of nebulous material, and to illustrate from his own observations how stars, once formed, showed signs of aggregating together into clusters, presumably under the ‘clustering power’ of their mutual attractions: “It is one and the same power uniformly exerted which first condenses nebulous matter into stars, and afterwards draws them together into clusters, and which by a continuance of its action gradually increases the compression of the stars that form the clusters.” Such ‘clustering power,’ as Herschel put it, would eventually break the Milky Way up into globular clusters, and the gradual progress towards this final condition might serve as a kind of universal chronometer to record the slow passage of the ages, in much the same as a conventional timepiece. And although we are not humanly aware of the rate at which this ‘cosmic clock’ marks out the passage of time, it was clear to Herschel that this process could not have happened forever: “Since the breaking up of the parts of the Milky Way affords a proof that it cannot last forever, it equally bears witness that its past duration cannot be admitted to be infinite.”

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This conclusion was quite at odds with the prevailing philosophical notion of the universe being infinite in both  extent and age. It was Herschel’s ultimate aim to extend the subject matter of astronomy to the remotest stars, far beyond the limits of the Sun’s dominion, but this led to an intense personal interest in the Sun itself. Indeed, Herschel regarded it as a typical star conveniently situated at close hand for our intimate scrutiny. The Sun had, of course, been recognized from antiquity as the resplendent source of light and life on Earth, and Newton in his theory of gravity had come to identify it as the source of the forces retaining the planets in their various orbits. The Sun’s distance from Earth, a quantity of great importance in astronomy, had been determined in Herschel’s youth, with an accuracy not previously attained, through observations of the planet Venus in transit across the solar disk. But, as we have seen, the investigation of the Sun as a physical object went back to the early 17th century, when Galileo and other pioneers of telescopic astronomy first systematically observed sunspots. The movement of the spots in its luminous surface, together with their daily motions, firmly established that the Sun is slowly rotating and enabled the axis of this rotation and its period to be determined (about 25 days). In observing the solar surface with his telescope, Herschel was obliged to protect his eyes with colored glass. In the course of his experiments to discover the most satisfactory type of shade he noticed that the sensation of heat seemed to have little relation to the intensity of the accompanying light but rather that it varied according to the color of the glass he employed. He further wondered if the variously colored rays that were generated by the prism might differ in their capacity to deliver thermal energy and whether the power of illuminating objects might not also be unequally distributed among such rays. To investigate the first of these possibilities, Herschel formed a spectrum of sunlight on a pasteboard screen that had a slot in it through which a narrow section of the spectrum, containing one specified color, would fall on the bulb of a thermometer below it. After a few minutes’ exposure to these rays, the reading on the scale of this instrument was compared with that of a second thermometer close to the first but shaded by the screen, and the difference in the readings was taken to indicate the heating power of the incident rays. This was done for red, green and violet light, the average heating effects being found roughly proportional to 55, 24 and 16, respectively. To compare next the illuminating powers of various colored rays of light, Herschel examined opaque objects bathed in light from various parts of the ­spectrum through a microscope, concluding that, in relation to the human eye, “the maximum illumination lies in the brightest yellow or palest green.” Herschel suspected that the heating effect, increasing towards the red, did not cease where the visible spectrum ended but continued well into the space beyond: “…the full read falls still short of the maximum of heat; which perhaps lies even a little beyond visible refraction in this case; radiant heat will at least partly, if not chiefly, consist, if I may be permitted the expression, of invisible light.” A month later he described how he had confirmed this view by experiment. The illuminated prism cast upon the table a solar spectrum to the red end of which

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Herschel brought up a stand, covered with ruled paper and supporting his three thermometers. One of these was exposed at various measured distances beyond the visible limit of the spectrum; the others were placed in line with the first but some way to the side. The exposed thermometer showed an excess of temperature over the others. There were therefore heating rays in the region beyond the visible red, the maximum effect of which being apparently located about half an inch beyond the spectral limit. Herschel also used his thermometers to explore the spectrum beyond the violet end of the visible spectrum but was unable to discover anything of significance. In conducting such experiments, Herschel had established the existence of infrared radiation as well as showing that the Sun emits more radiation at green wavelengths than at any other visible light wavelength. In so doing, Herschel contributed to advancing our knowledge of the electromagnetic spectrum and its application to astrophysical phenomena. Herschel also pondered the mystery of the Sun’s ‘internal construction.’ The sunspots appeared to offer the most hopeful clue, but in those early days a number of conflicting views as to their nature had been entertained. In 1774 Alexander Wilson, professor of astronomy at Glasgow, had been led by his observations to regard a sunspot as a depression in the Sun’s surface, revealing a non-luminous layer below. The shaded border of the spot, what we might call the penumbra, represented the ‘shelving sides’ of the depression. In this scheme of things, Wilson conceived the Sun as a solid, dark sphere enveloped by a thin, luminous covering. A sunspot, Wilson asserted, was a rift in this envelope caused by the generation of some gas within. On the other hand, the French astronomer, Jerome Lalande, writing 2 years later, considered them as rock-like projections from a solid core alternately exposed and submerged by the ebb and flow of a fiery liquid surrounding the Sun and with the penumbra representing the surrounding shallows. Herschel’s first paper on the constitution of the Sun, which was presented in 1794, offered observational evidence that the Sun was a dark body surrounded by an extensive atmosphere. This was composed of several ‘elastic fluids,’ one of which was luminous and the rest transparent. So, to Herschel’s way of thinking, the luminous fluid might be generated by the decomposition of gases somewhat as (he supposed) clouds are formed in our own  atmosphere, or it could correspond to the wonderful natural light shows we call the aurora borealis/australis. In much the same way as we can see through our atmosphere from above, he conceived the spots as rifts that appeared in this bright envelope through which we could see the dark surface of the Sun. The bright patches, or faculae, apparently elevated above the mottled surface of the Sun, Herschel regarded as local accumulations of this luminous material. The wastage of the Sun’s light might perhaps be made good by the diversion into the Sun of some of the numerous comets, which appeared to consist merely of luminous vapors. Herschel also observed the tiny cells that make up the solar surface but bizarrely thought them to be alive, as they were constantly morphing, appearing and disappearing with the passage of time. That something could actually live on the surface of our star seems utterly preposterous to us today, but in Herschel’s era next to noth-

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ing was known about the extraordinary complexity within even the simplest living thing, as well as their sensitivity to extremes of temperature. To the objection that the Sun dwellers would be consumed by the intense solar heat, endured at such close quarters, Herschel surmised that the Sun’s rays produce heat only when they enter an appropriate medium, such as Earth’s atmosphere. Herschel was writing much in the spirit of the prevailing 18th century notion that divine providence had crammed every nook and cranny of the cosmos with some appropriate form of life. In this capacity, Herschel also extended the attribute of habitability from the nearby Sun to the distant stars. It made sense to Herschel that the Creator would cause many worlds to be inhabited. Herschel’s views on the nature of the Sun underwent a further development in a paper dated to 1801 in which he advanced the notion that the Sun’s behavior might be correlated to forecasting good or bad harvests on Earth. His observations were shared for a time by Patrick Wilson who, after succeeding his father, Alexander Wilson, in the Glasgow Chair of Astronomy, had retired and settled in London, visiting Herschel at his home at Telescope House, Slough. Just a few years earlier in 1796, Wilson had rebuked Herschel for not acknowledging his father’s priority in establishing the nature of the sunspots, but was satisfied by the astronomer’s explanation, and the two subsequently became good friends. Herschel can also rightly be considered one of the earlier pioneers of spectroscopic astronomy. In 1799 he attached a prism to the eyepiece of one of his telescopes and observed the colors into which it resolved the light of six stars of the first magnitude, noting the preponderance of red in the star Betelgeuse, orange in Arcturus, or blue in the case of Procyon. He did not, however, note any spectral lines. As we have seen, though living somewhat in the shadow of her famous brother, Caroline Herschel became an accomplished observer in her own right. Her earliest observations were conducted with a small refracting telescope, similar to a ship captain’s spyglass. But on August 22, 1782, she began sweeping the skies with a small telescope built by her brother and adapted for sweeping. The instrument was a 4.2-inch rich-field reflecting telescope, with a focal length just short of 2  feet. Contrary to widespread claims, its speculum mirrors, when freshly polished, were only moderately less reflective than modern coatings. And as for optical quality, William Herschel was indisputably one of the greatest telescope makers of all time. Caroline also used a small achromatic refractor in her deep sky sweeps. Caroline identified her targets using an eyepiece that delivered a 2°15′ field of view either at 15× (according to Caroline) or 24× (according to William). Then she would examine them in greater detail at double that power. Her task was to sweep for comets, and she began to write down and describe all remarkable objects and structures she saw during the course of her sweeps. William also instructed her to search for double stars, star clusters and nebulae and encouraged her to describe their positions by drawing imaginary lines from certain reference stars and figures drawn on paper. During these sweeps, Caroline kept Messier’s list of nebulous objects continually by her side. This list, published in 1784, was a gift to her brother

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from the London businessman and prominent amateur astronomer Alexander Aubert soon after its appearance. The sheer scale of Caroline’s contributions to astronomy is impossible to overestimate. Dedicated to her brother and her own work, Caroline would walk to and from William’s observing quarters – a distance of just over half a mile away, which must have been trying in bad weather. Indeed a rumor began to circulate in Slough that the son of the owner of one of the houses in the High Street where she lodged for a short time, would tell how, as a young lad, he was sometimes roused in the night by her rap on the wall, when the weather, which had at first been cloudy, cleared up. Knowing the signal, he would get up, light a lantern, and descend the stairs, only to find her ready and dressed and awaiting him. He perfectly recalled her gentle manner of saying to him, “Please will you take me to my Broder.” When Caroline first started sweeping the night sky, she felt that she “knew too little of the real heavens to be able to point out every object so as to find it again without losing too much time by consulting the Atlas.” This was most disturbing when her brother was away: I was, of course, left solely to amuse myself with my own thoughts, which were anything but cheerful… But all these troubles were removed when I knew my brother to be at no great distance making observations with his various instruments on double stars, planets, etc., and I could have his assistance immediately when I found a nebula or cluster of stars, of which I intended to give a catalogue.

Observing with her brother’s colossal telescope at Slough was not without its risks, however, as on one occasion we learn that Caroline tripped and fell on a snow-­ covered field in the dead of night and impaled her leg on a large iron hook that was used to adjust the position of the instrument. Caroline’s telescopic discoveries were relatively few at first. During her first night of observing, she found one of her brother’s double stars. Then, on September 30, she encountered a few more double stars and her first comet impersonator – the 27th object in Messier’s list. By October she had added M36 and M13 to her repertoire. By January 1783, she was clearly beginning to enjoy her time under the stellar canopy. It was on the evening of February 26, 1783, that Caroline’s made her first discovery. On that night she recorded a nebula not listed in Messier’s catalog with a small refractor and promptly showed it to her brother. The object, known today as the open cluster NGC 2360 (Caldwell 58) was the first of 14 deep sky objects Caroline Herschel would discover, 11 of which had never been seen by any human eye. The identity of some of these objects have mystified modern scholars, however, prompting much controversy over which objects truly existed and which should be attributed to Caroline and not her brother. That said, the matter seems to have now been satisfactorily cleared up by the historian of astronomy, Michael Hoskin, in the November 2005 Journal for the History of Astronomy. What follows are some brief notes on these objects, all discovered between 1783 and 1787. In respect of NGC 2360, her notes reveal, “Following γ Canis majoris, a very faint Nebula,” but then goes on to describe her brother’s observations of the same object, presumably made through a much larger instrument.

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M48 was the last object that Caroline “discovered” with her small refractor. Her notes say “At an equal distance from 29 & 30 Monocerotis, making an equilateral triangle with those stars in a nebulous spot. By the telescope it appears to be a cluster of scattered stars.” The stars 29 and 30 Monocerotis are now usually called ζ Monocerotis and C Hydrae, respectively, and there’s little doubt that the cluster in question is the one we now refer to as M 48. Messier’s original catalog gave incorrect coordinates for this object, so she and William assumed that this was an original discovery. As this author interprets Caroline’s description, she located M48 with her unaided eyes before turning her telescope to it. Caroline discovered NGC 6866 and the remaining objects with her 4.2-inch comet sweeping reflector. Her notes include coordinates that lie just a half degree south-southwest of NGC 6866 after factoring in the effects of precession. But she also wrote, “…some small stars, or perhaps a Nebula. My brother put, I believe, a power of 70 to the Sweeper, then what is call’d some small stars are about a hundred or more.” Apparently she found resolving the cluster into individual stars to be difficult at low magnification but easy at 70×. This jibes well with the findings of contemporary observations of the same deep sky object. Caroline found NGC 6633 “about halfway from S Serpentarii [71 Ophiuchi] towards θ Serpentis.” She saw “…a Cluster of large stars. I counted around 80.” To the modern reader it is somewhat intriguing that she didn’t also mention neighboring IC 4756. This IC cluster was discovered much later from the examination of photographic plates. That said, IC 4756 is quite an easy target for modern observers using small instruments. In fact, it can even be seen by the unaided eye from a dark sky site. But presumably 18th- and 19th-century astronomers weren’t expecting star clusters to be so large and loose. William Herschel could easily have missed this cluster because his ‘scope’s field of view was so small, but Caroline’s comet sweeper would have framed IC 4756 perfectly at low power. IC 4665 is pinpointed precisely by Caroline’s notes. She writes, “A cluster of stars. I counted about 50 in the field; rather more than less.” William had in fact observed this cluster through a larger telescope that same night and reported: “It consists of about 14 or 16 large ones with several very small ones between. … Lina found it.” In retrospect, this cluster and NGC 663 had been recorded earlier by Philippe Loys de Chéseaux, but the observations were not published at the time. Charles Messier drew M110 on a sketch of the Andromeda Galaxy, but he didn’t include it in his published catalog, so Caroline was unaware of his prior discovery. Her notes read: “About ½ deg preceding & a little north of Mess 31st a nebula.” NGC 253 is one of the brightest galaxies in the sky, and a splendid sight from southerly latitudes, where it rises high in the sky. But it was a tough find for Caroline Herschel, who couldn’t have seen it more than 12° above the southern horizon. She described it as “a faint nebula below the 2nd Triangle under β Ceti….Mess. has it not.” NGC 225 was the first of three clusters in Cassiopeia that Caroline observed on the evening of September 27, 1783, and which were re-observed on October 30. William didn’t see any of these objects at the time, so any identifications that he

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made with clusters from his own catalog must have been derived from his sister’s written or mental recollections. Caroline’s notes from October 1783 pin down the location of the first cluster quite precisely: “1 ½ deg. from γ toward κ Cass. (by the finder) the first cluster of Septr 27th.” NGC 225 is almost directly between these two stars, and it’s easy to see in small telescopes, so there’s no real doubt about the identity of this cluster. True, the distance from γ Cas is actually 1.9° rather than 1.5°, but this represents a distance error of only 30 percent. The September notes describe the location rather differently: “About 2 degrees from γ Cassiopeia making an Isosceles triangle with γ & κ, a small cluster of stars, seemingly intermixed with nebulosity.” NGC 225 is indeed nearly equidistant from these two stars, but it’s odd to describe what is, in effect, a straight line as the legs of an isosceles triangle. It’s true that Caroline could fit her cluster in the same field of view with either star individually, but couldn’t fit all three together. So she might indeed have determined that the distances were equal without noticing that they were also in a straight line. Another possibility is that Caroline observed some cluster or asterism other than NGC 225 on the same evening of September 27. NGC 189 is even more mysterious. For one thing, William identified Caroline’s second Cassiopeia cluster as NGC 381, but this is nowhere near the location that she indicated in her notes. What Caroline actually wrote on September 27 was: “About 1° south of the above cluster a faint nebula surrounded with a great number of both large and small stars. There are more large stars in the field than are marked here but I took particular notice of the two between which the nebula is situated.” If Caroline’s first cluster was NGC 225, then NGC 189 is an excellent match for the location. But NGC 189 is not between two bright stars, and at magnitude 8.8 it would have been rather difficult to observe through her modest telescope. NGC 659 is credited to Caroline in William Herschel’s published catalog, but some researchers express doubts about the identification. For example, her notes from September 27 say: “δ and ε Cassiopeiae & χ Persei making a trefoil. A cluster of stars in the middle.” And on October 30 she wrote: “I saw the cluster which is placed between delta & ε Cassiopeiae and χ Persei (a crouded place).” The star that the Herschels mistakenly called χ Persei was in fact 7 Persei. This star forms an extended triangle with δ and ε. Cassiopeiae. NGC 659 is indeed inside this triangle, but it’s far off to one side. However, NGC 659 is quite hard to resolve in a small telescope at low magnification, and so it’s difficult to imagine viewing NGC 659 without noticing its much bigger and brighter neighbor, NGC 663, just 0.5° away. There is indeed a cataloged cluster near the center of the triangle formed by δ Cas, ε Cas, and 7 Per, namely NGC 743. But this cluster was first sighted by John Herschel, William’s son, long after William had identified Caroline’s cluster as NGC 659. Perhaps William came to this conclusion because of the three clusters that he did observe in this area (NGC 654, 659 and 663); this is the one that’s closest to the triangle’s center. What is the best candidate for a star grouping between δ Cas, ε Cas, and 7 Per that’s well seen in a small telescope? It might be an asterism rather than a true clus-

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ter. As Caroline reported, central Cassiopeia is “a very crowded place.” But such vague references are frustrating to the modern scholar. Dazzled as we are by John Herschel’s accomplishments, it’s easy to forget that they were not seasoned deep-­ sky observers at this point in time. All they had to guide them was the thin catalog that Charles Messier had just published. Yet even the most experienced observer, armed with modern charts and catalogs, can wind up confused by the swarms of stars in this part of the sky. There’s no such doubt about NGC 752, which Caroline noted as: “About 3° south of γ Andromedae, a fine Cluster of Stars.” The actual distance is 4.5°, but otherwise NGC 752 matches this description perfectly. NGC 7789, perhaps the loveliest of Caroline’s discoveries, features in her notes as follows: “Between σ and ρ Cassiopeiae is a fine nebula, very strong.” It’s intriguing that she described it as a nebula, since it must have been very nearly resolvable in her telescope. Had her brother examined it with a higher-power eyepiece, he might have easily seen that NGC 6866 is most definitely not nebular in nature! NGC 6819 is located “halfway between δ Cyg & η & θ Lyrae making an isosceles triangle downward when in that situation,” just as Caroline noted. She described it as a star cluster but gave no details. NGC 7380 is noted in William’s catalog as one of Caroline’s discoveries, but it’s quite a bit off the position described in her notes: “I saw a nebulous patch in a line from ε Cephei continued through δ towards 1st and 2nd Fl. Cassiopeiae.” A line from ε through δ Cephei has to take a pretty sharp turn to reach NGC 7380. Perhaps the usually careful Caroline really meant ζ rather than ε Cephei. Caroline also discovered eight comets, six of which bear her name. These are: Comet C/1786 P1 (Herschel), discovered on August 1, 1786 Comet 35P/Herschel-Rigollet, co-discovered by Caroline on December 21, 1788 Comet C/1790 A1 (Herschel), discovered on January 7, 1790. Comet C/1790 H1 (Herschel), discovered on April 18, 1790. Comet C/1791 X1 (Herschel), discovered December 15, 1791 Comet C/1793 S2 (Messier) discovered October 7, 1793 Comet C/1793 S2 (Messier), first sighted by Caroline on November 7, 1795. Comet C/1797 P1 (Bouvard-Herschel), discovered August 14, 1797 Unlike the star clusters and nebulae Caroline discovered with small, rich-field telescopes, her comets were almost invariably discovered using a 9-inch Newtonian reflector of 5 feet focus, designed and built by her brother, but only magnifying 25 or 30 times. In August 1799, Caroline was independently recognized for her work after spending a week in Greenwich as a guest of the royal family. After her brother died in 1822, Caroline was grief-stricken and moved back to Hanover, Germany, continuing her astronomical studies to verify and confirm William’s findings and producing a catalog of nebulae to assist her nephew, John Herschel, in his work. However, her studies were compromised by the imposing buildings of the city, and she spent most of her time working on the catalog. In 1828 the Royal Astronomical Society presented her with their Gold Medal for this work. No woman would be

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awarded it again until 1996 when the American astronomer, Vera Rubin, received the same accolade. Upon William’s death his son, John Herschel, took over observing at Slough. Caroline had given him his first introduction into astronomy, when she showed him the constellations in Flamsteed’s atlas. Caroline added her final entry to her observing book on January 31, 1824, about the Great Comet of 1832, which had been discovered on December 29, 1823. Throughout the twilight of her life, Caroline remained physically active and healthy, and regularly socialized with other scientific luminaries. She spent her last years writing her memoirs and lamenting her body’s limitations, which kept her from making any more original discoveries. Caroline Herschel died peacefully in Hanover on January 9, 1848, aged 97 years and 10 months. She was buried at 35 Marienstrasse in Hanover at the cemetery of the Gartengemeinde, next to her parents and with a lock of William’s hair. Her tombstone inscription reads, “The eyes of her who is glorified here below turned to the starry heavens.” With her brother, she discovered over 2,400 astronomical objects over two decades of active observing. The asteroid 281 Lucretia (discovered 1888) was named after Caroline’s second Christian name, and the crater C. Herschel on the Moon was also named in her honor. William was 54  years old when his son, John Herschel, came to Slough. But what a world he grew up in, surrounded by scientific instruments and workshops of all kinds at Observatory House. By then his father had long abandoned his musical career and was already a grand amateur, enjoying considerable wealth and recognition throughout the scientific world. This is where John was schooled and spent much of his childhood. By and large, John was a quiet and rather lonely child, although he did form warm and enduring bonds with his two cousins, Sophia and Mary Baldwin. As well as making sure he was proficient in French, his father was keen for his son to master the German tongue as well as the usual Latin and ancient Greek. He also received a good musical education from his father. But as well as showing a great aptitude in linguistics and music, John exhibited quite an early flare for mathematics and mechanical invention, pestering his father’s technicians to find out how their tools worked. Still, with no other children to play with, his formative years must have been at times lonely and rather bookish. In 1800, at age 8 years, John was packed off to Eaton, a prestigious school for boys, but within a few months he left on account of the rather cruel academic regime he encountered there. At age 17, John left home to attend St. John’s College, Cambridge, where he first encountered young men of his own age. Here he developed a strong competitive spirit, distinguishing himself in classics but also receiving the coveted rank of Senior Wrangler, winning the Mathematical Tripos in 1813. It was during his time at Cambridge that John Herschel campaigned for the introduction of the Leibnizian form of calculus over the more antiquated Newtonian notation, as it proved far more versatile than the latter. After graduating, he took up a fellowship at St. John’s and was elected a member of the F.R.S. for pioneering work in optical theory and in particular, on improvements in the design of the achromatic lens. But in his early twenties, he developed bronchitis and rheumatic bouts that left him quite weak and

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that plagued him for the rest of his life. John initially had high ambitions to cut his own path in life and not to live in the shadow of his illustrious father, deciding at first that he would not pursue astronomy as a career. But in August 1816, after joining his 78-year-old father and his household in a holiday house in Devon, he was obliged to assist Sir William in completing his work on the nature of stellar systems. The first task his father set him when he returned to Slough from Cambridge was to rebuild an 18-inch reflector, which he began work on in the fall of 1816, and by 1820, he had ground and figured a good speculum metal mirror. It was a different matter for the 48-inch telescope, however, which by now remained idle and dilapidated on the grounds of Observatory House. Truth be told, the great telescope never lived up to its potential and indeed remained idle up until 1839, when John had it photographed before it was dismantled permanently. While John learned a great deal of practical skill in the operation of large telescopes from his father, he was also instructed by Sir James South in the use of the new line of equatorially mounted refractors, one of which was set up at South’s grand home at Blackman Street Observatory, Southwark. By the early 1830s, the newly knighted Sir John Herschel had ascended to the zenith of his career as Grand Amateur, enjoying much notoriety on the international stage. His opinions were sought across a dozen scientific and philosophic fields and warmly encouraged less privileged individuals to make their own contributions to the scientific literature. In particular, John went out of his way to encourage the Scottish science writer, Mary Somerville (1780–1872) to publish her books and papers. Sir John did much to put the various astronomical societies that were springing up across Britain on a firmer footing. Indeed, together with Francis Baily and William Pearson, Sir John established the Royal Astronomical Society (RAS) in 1820. After completing work initiated by his father on cataloging the nebulae, Sir John turned his attention to the increasing body of data from observers in Britain, Germany, France and Russia, that the binary stars were showing signs of dynamical change. Indeed by 1825, the binary system Eta Coronae Borealis had undergone a full revolution in the four decades since Sir William had first turned his large telescopes upon it, and by 1830 Felix Savary had shown that the secondary star in the system Zeta Ursae Majoris was moving in accordance with Newton’s laws of motion. Soon after this, Johann Encke, based in Berlin, had demonstrated much the same thing with the binary system 70 Ophiuchi, with its orbital period of just 88 years. These exciting developments prompted Sir John to issue a pamphlet in 1832 reducing the data for several stellar orbits that were amenable to study by suitably equipped amateurs. Although much of this precision work was being undertaken using long -focus achromatic refractors astride sturdy, clock-driven equatorial mounts, it is important for the reader to appreciate that much of the groundbreaking work on binary stars was done by Sir William Herschel using his 18-inch reflector of 20-foot focus, but also by Sir John Herschel using his own 18.25-inch reflector during the 1820s.

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These observations were not intended, however, to reveal the orbital elements so much as to highlight their existence. When it came to making precise measurements of the angular separation or position angle of such pairs, Sir John resorted to using an equatorially mounted refractor of 7-foot focus. Unlike the nebulae, which appeared to the eye in a vast array of different shapes and sizes, studying the orbital elements of binary stars very much appealed to Sir John’s mathematical bent, yet he remained fascinated with the nature of conspicuous objects in the heavens such as the Great Nebula in Orion, upon which he conducted innumerable observations over the space of nearly two decades with telescopes as large as 18 inches in aperture and which were first summarized in a marvelous treatise authored by him in 1826. In particular, Sir John hoped that it would serve as a benchmark that other astronomers might use to detect changes in the structural features of the nebula. Since there was no way of estimating the distance of the Orion Nebula at that time, the affirmation of changes within the same would indicate that it was located relatively near the Solar System, and if not, it would have to be located much further away. Sir John also pondered the nature of the new class of objects that had been discovered by his father, the planetary nebulae. His observations of some of the more prominent members of this class, particularly M97, which stubbornly refused to resolve into stellar subunits even through the most powerful telescopes then available, presented a profound mystery to him. How can an object so devoid of stars become incandescent? In an age where astrophysics was still in its infancy, he seems to have concluded that these non-stellar nebulae must be composed of tiny dust particles, softly glowing in the empty space between the stars. With the death of his mother in 1832 and after the publication of his great catalog of nebulous objects in 1833, Sir John felt that his observational work in the northern hemisphere ought to be extended to the include a new survey of objects appearing below the equator. So on November 13, 1833, Sir John, his wife, Lady Margaret (nee Brodie Stewart) and their young family, observing assistants and a vast array of astronomical gadgetry boarded the Mountstuart Elphinstone, which departed Portsmouth for an 8-week voyage to the Cape, South Africa. After purchasing the Feldhausen estate (a suburb of Cape Town) outright, he and his assistants quickly set to work erecting the same large telescope – the 18-inch speculum – he had employed so successfully at home in Slough. Here he ­collaborated extensively with the Astronomer Royal for the Cape of Good Hope, Thomas Maclear (1794–1879) and befriended his family. Over the next 4 years, between January 1834 and March 1838, Sir John achieved a complete survey of the southern skies, discovering and cataloging a wealth of novel celestial objects. Early into such surveys at the cape, Herschel noted that the nebulae were far more evenly distributed than they were in the northern hemisphere, the latter being especially concentrated in the constellations of Virgo, Leo, Coma Berenices and Ursa Major. Sir John was particularly captivated by the Large and Small Magellanic Clouds, which simply had no equal in the northern heavens. Lady Herschel, herself an accomplished naturalist, produced her own contributions to botanical knowledge in beautifully rendering no fewer than 131 watercolor paint-

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ings of new fauna. And whereas the northern skies only yielded about half a dozen planetary nebulae, its southern counterpart yielded far more, so much so that by 1835 they had become almost blasé about properly recording them! The extensive telescopic surveys conducted while at the Cape proved formative for Sir John, who had come to believe that many nebulae could not be mere stellar aggregations. What is more, and departing from the conclusions drawn by his father, Sir John had now come to believe that the Sun and its retinue of planets could not be at the center of the universe. What’s more, beginning around 1836, Sir John employed an ingenious apparatus, which he referred to as an ‘astrometer,’ to make the first photometric measures of stars, concluding that Vega and Arcturus were both intrinsically more luminous than the Sun by factors of 40 and 200, respectively. In so doing, he departed from the conservative view adopted by his father; that all stars were effectively the same and that their varying brightness always reflected their differing distances from the Solar System. The return of Sir John to England in the spring of 1838 effectively brought to an end a 21-year long career as an observational astronomer, and though some of his peers continued to build bigger and more powerful telescopes, Sir John expressed no such interest in outgunning the achievements of his father. Ironically, it was one of his father’s handy short focus reflectors that he turned to for casual observing. Observatory House, Slough, was now becoming an overcrowded place, what with the arrival of several more children born to Lady Mary and Sir John and the steam locomotive had finally come to town, making inroads into the family’s cherished privacy. These changes impelled the Herschel family to move to a large country estate at Hawhurst, Kent, which Sir John purchased in August 1839. It was here that he continued to reduce and tabulate his seminal astronomical work conducted in South Africa, which was eventually published in 1847. The ailments that had hampered him since his youth – bronchitis, rheumatism and sciatica – were now compounded by varicose veins that made him far less active at 60 than his father ever was. And though he remained a scientist of international repute, Sir John’s role became more of an elder statesman than anything else, continuing as he did to encourage younger men of promise, including James Nasmyth, William Lassell, and Lord Rosse. Further, he greatly enjoyed the company of distinguished observers such as the Reverend William Rutter Dawes and Admiral William Henry Smyth, gentlemen we shall have more to say about later in the book. The Herschel astronomical dynasty lasted up until the beginning of the 20th century. Sir John Herschel’s son, Alexander, was born in South Africa in 1836 during one of his father’s surveys of the southern skies. He became a professional astronomer in his own right, having been educated at Trinity College in Cambridge, England. Alexander was a professor of physics at the University of Durham and did original research in meteor spectroscopy and cometary science and became a close confidant of the prolific observer, William F. Denning. Although the Herschels’ giant telescopes quickly fell into disuse by the mid-­ 1850s, their far-reaching legacy was carried on across the Irish Sea with another dynasty of giant telescope makers. Enter the Earls of Rosse at Parsonstown, the subject of the next chapter.

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Sources Bennett, J.A.: On the power of penetrating in to space: the telescopes of William Herschel. J. Hist. Astron. 7, 75–108 (1976) Chapman, A.: The Victorian Amaeur Astronomer. Gracewing (2017) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Hoskin, M. (ed.): Caroline Herschel’s Autobiographies. Cambridge, Science History Publications (2003a) Hoskin, M.: Herschel’s 40ft reflector: funding and functions. J. Hist. Astron. 34, 1–32 (2003b) Hoskin, M.: Discoverers of the Universe: William and Caroline Herschel, vol. 2011. Princeton University Press, Princeton (2011) King, H.C.: The History of the Telescope. Dover, New York (1955)

Chapter 9

Thinking Big: The Pioneers of Parsonstown

Dedicated to the Memory of Peter Grego (1966–2016) The picturesque, rural town of Birr in the county of Offaly lies at the geographic center of the Irish Republic. Inhabited in some capacity since the Bronze Age, a monastic settlement was established there by St. Brendan the Elder, which probably dates to the 7th century a. d., and in the centuries that followed, Birr became the ancestral home of the O′ Carroll clan, the ruling Gaelic family of the northern territory of the ancient kingdom of Éile. In the aftermath of the Norman invasion of the twelfth century, a castle was built there and continued to be administered by the O’Carrolls, who were required to pay tribute to the Butlers of Ormonde. The Butlers were overlords of the district, whose capital was established in the neighboring county of Kilkenny. In the aftermath of the so-called English Plantation of Ireland in the seventeenth century, when wealthy Protestants acted as the new overlords of vast tracts of Irish land, Birr Castle became the seat of the Parsons dynasty, the Earls of Rosse, beginning in 1620. It was at this time also that the civic areas around the castle were annexed to it, when it subsequently became known as Parsonstown (Fig. 9.1). From the seventeenth century onwards the Gaelic Irish were reduced to the status of tenants and landless peasants on their ancestral lands. Members of the O’Carroll clan were, however, granted new lands in the colonies of Maryland, and one family descendant, James Carroll of Carrolltown, went on to become the sole Catholic signatory of the American Declaration of Independence. Evidence of British colonial rule can still to be seen in the elegant Georgian architecture of the modern town, with its tree-lined malls and well-planned avenues, which still have the power to delight the eye today. A railway, printing works and distillery provided employment to local families and a workhouse offered some relief to the starving peasants, a million of whom lost their lives during the famine years. A garrison of English soldiers was also established in the town. But like all Irish municipalities once administered by the iron fist of British Imperialism, the © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_9

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Fig. 9.1  Birr Castle, the ancestral home of the Earls of Rosse. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/File:Birr_Castle,_Offaly.jpg)

political winds of change swept rapidly through the region, as agrarian agitation by the Fenians, Land League and the Irish Parliamentary Party, led to the dissolution of the landlord system, which also included the estate of the Earls of Rosse. As a symbolic act of the new order, the Gaelic Athletic Association also held the first All-Ireland Hurling Final at Birr in 1888. Remarkably, though its population was decimated in the mid-nineteenth century owing to the ravages of the Irish potato famine (1845–1852), the modern town of Birr, the inhabitants of which number about 6000, has scarcely grown in size from its pre-famine population, making it one of the most pristine Irish heritage towns in existence. After Birr Castle became Crown property in 1620, the Parsons family held several key offices in the administration of Ireland. William Parsons became Commissioner of Plantations and Surveyor-General of Ireland. His brother, Sir Laurence Parsons, became Attorney-General for the province of Munster, and in the years that followed, the castle was considerably enlarged and a successful glass works established, which further aided the local community with employment opportunities. In the aftermath of William Parsons’ death in 1628, Birr became the epicenter of conflict between Catholics and Protestants. In 1641, a rebellion by Irish Catholics broke out, and by January 1642, the castle itself was besieged by the Molloys, Coghlands and Ormonders, the factions engaging in brutal combat for five long days. In some desperation, the noble incumbent, William Parsons, son

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of Sir Laurence, fled to the English army stationed at Dublin, and never returned. He died in 1653. The troubles escalated during the tenure of William’s son, Laurence, who took up residence at Birr Castle after his father’s passing. This time, England was faced with the prospect of crowning a Catholic king, the Duke of York, who became James II in 1685. Laurence Parsons and his family departed for London, leaving an unscrupulous heathen in charge of running the family estate at Birr, a one Colonel Heward Oxburgh who, in 1689, seized complete control of the castle and its garrison, using it as a base for the forces loyal to William of Orange. Sir Laurence, together with two of his confidants, were placed on trial by Oxburgh, accused of being traitors to King James II, the last Catholic king to rule the British Isles, but were later granted a reprieve and were rescued by William’s men. More turmoil followed in 1690 when the castle was once again besieged by an army led by the Duke of Berwick, an illegitimate son of James II, who himself was not long after deposed in the Glorious Revolution of 1688. During the exchange of fire, cannon balls flew through the parlor window, leaving marks in the walls of the north flanker that can still be seen to this day. Lady Parsons was even forced to relinquish the lead cistern she used for salting beef so that it could be melted down for bullets. Eventually, though, the besieging army was finally repulsed, and the Parsons family returned to relative peace thereafter. The bloody events of the seventeenth century marked a watershed in the history of the castle, as well as the family who made it their home. But a new dynasty of Parsons was to emerge from the ashes. Throughout the eighteenth century, Birr castle became a popular haunt for some of the must cultivated individuals in Europe. Sir William Parsons, the 2nd baronet (in the new regime), was a close friend of the gifted composer, Georg Frideric Handel, who gave him an engraved walking stick in appreciation of the patronage that led to his magnum opus – Messiah – being first performed in Dublin. His grandson, another Sir William, the 4th baronet, began an ambitious project of landscaping the grounds of Birr Castle. Transforming bog land into an ornate lake, he planted beech trees and demolished the last of the ancient towers of the original fortress in order to complete the sweeping view of the demesne. Sir William also devoted much of his time to the volunteer movement, which sprang up towards the end of the eighteenth century, ostensibly to defend Ireland from the threat of French invasion but effectively to force the English government to give concessions to the Irish Parliament. His son, Sir Lawrence, 5th baronet, became well known as a patriot statesman, whose friend and colleague, the Irish revolutionary, Theobald Wolfe Tone (1763–1798), referred to him as “one of the very few honest men in the Irish House of Commons.” This personal integrity led him not only to oppose the Union with all his strength, but also to expose the bribery the British used to push it through. Evidently disgusted with the passing of the Act of Union in 1800, Sir Laurence retired from politics at the beginning of the nineteenth century, though he later accepted the post of Joint Postmaster General and attended the laying of the foundation stones of Dublin’s magnificent General Post Office built during his term of office. He devoted the autumn years of his life to literature, especially as an apologist of the Christian faith.

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Fig. 9.2  Sir William Parsons (1800–1867), third Earl of Rosse. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ William_ Parsons%2C_3rd_Earl_of_ Rosse#/media/ File:William_ Parsons,_3rd_Earl_of_ Rosse_photo.jpg)

Sir Laurence, the second Earl of Rosse, had three sons, the eldest of whom, William (also known as Lord Oxmantown), succeeded his father as third baronet upon his death in 1841. Unlike his father before him, the third Earl had a penchant for all things scientific, especially astronomy, and we learn of his first forays in the art of telescope making as early as 1827. The illustrious career of Sir William Herschel (1738–1822) proved to be a huge influence on the young William Parsons (1800–1867), inspiring him to read mathematics at Trinity College, Dublin, where he graduated with a first class honors degree in 1822. And although he resolved to embark on a scientific career, his baronial status required that he participate in public life. To that end, he entered Parliament for King’s County (later renamed Offaly) in 1823, where he enjoyed a reasonably successful career, which he brought to an end in 1834. Two years later he married the fabulously wealthy Mary Wilmer-Field, who hailed from Heaton, Yorkshire. The marriage was a long and happy one, and together they had four sons, all of whom displayed considerable intellect in adult life. Lady Mary was also a gracious host for all the scientists who were to work at Birr, and took an active interest in the work of her husband. The couple took up residence at Birr Castle after William’s parents retired to Brighton, England, in search of milder climes. As master of his own baronial home, William was free to pursue his scientific career (Fig. 9.2). William Parsons lived in a singularly interesting time for telescopic astronomy. Refracting telescopes were justifiably popular, especially after the innovations heralded by the genius of Joseph von Fraunhofer (1787–1826) in Germany, who had brought high quality achromatic refractors to market astride state-of-the-art clock-­ driven mounts that gracefully tracked celestial objects as they moved across the sky. But Parsons was a scientist, and he was compelled to pursue reflectors rather than refractors owing to the very limited aperture of the latter. He wanted to see the nebu-

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lae of Messier and Herschel better than anyone before him. Perhaps he had seen too many of his astronomical acquaintances follow the fashions of the time; which almost invariably involved double star mensuration with small -aperture refractors. Indeed, according to the late Sir Patrick Moore, he completely abandoned the refractor early in his astronomical career. Parsons had clearly decided to go after bigger fish, and became firmly convinced that mirrors were the way to do it. And to that end, he assembled a small work force under the aegis of a local blacksmith, William Coghlan, and constructed turf powered furnaces for the creation of the speculum alloy before it was figured and polished. The financing for these ambitious projects came from his beloved wife, without whose wealth he could never have undertaken such marvelous engineering works. Like many astronomers of his day, Lord Oxmantown had to learn the noble art of casting and grinding mirrors to the required geometrical shape more or less from scratch. He was vociferous about making the details of the construction of fine optical wares public knowledge, condemning the often secretive culture of telescope makers who came before him. As was the custom in those days before silver-on-­ glass reflectors, he had to use speculum metal mirrors consisting of an alloy of copper and tin as the reflective surface. To this end, he employed his considerable inventiveness to construct a steam-powered grinding machine with a power output of 2 horse power (about 1.5KW). The mirror blank, placed in a vat of water to prevent its overheating and expansion, was rotated slowly by the contrivance while the polishing ‘tool’ was made to move to and fro across the metal surface by a couple of cranks placed at right angles to each other, delivering 16 strokes per minute. By considerable trial and error, Oxmantown was able to construct a series of increasingly large specula, first a 15-inch and then a larger 24-inch, both of which were of a novel, segmented design, and proved to be of very high quality. Indeed, in a paper published in 1840, Oxmantown communicated that the 15-inch delivered excellent views of the Moon at 600x! Unlike Herschel before him, who had dispensed with the use of a secondary flat mirror in order to conserve the amount of light reaching his eye, and which gave rise to the tilted mirror of the Herschelian design, Lord Oxmantown returned to the closed-tube Newtonian configuration, finding out by experiment that it reduced turbulence on account of the observer being located at a large enough distance from the mouth of the open tube. He also showed that tilting the mirror in the Herschelian fashion introduced unwanted aberrations to the images that were dispensed with in the Newtonian design. His mounting strategy, however, was quintessentially Herschelian in form, with all its attendant weaknesses. After many false starts and setbacks, he managed to cast and figure a fine 36-inch speculum with a focal length of 27 feet (f/9 focal ratio) in 1839. The mirror was an alloy of 126.4 parts copper with 58.9 parts tin which produced a fine, white metal. The optical flat mirror was tested by comparing a distant object in daylight, first with a fine achromatic telescope and then using the same telescope that had formed an image after its reflection in the mirror. Any distortions would have been readily seen and adjustments accordingly made. Oxmantown also designed and constructed

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the world’s first segmented mirror of 36-inch aperture. Sadly, the mirror never saw first light but can be seen at the Science Museum at Birr Castle, where it is proudly displayed for public inspection. After mounting the optics, Oxmantown’s friend, the distinguished mathematician (a pioneer in vector algebra), William Rowan Hamilton (1805–1865), whom he became acquainted with during his time at Trinity College, was the first to turn it on celestial targets, and later pronounced it as excellent. Lord Oxmantown also invited the distinguished astronomers Sir James South (of double star fame) and Thomas Romney Robinson to his estate at Birr Castle in order that they might test the telescope and pronounce assessments of its quality. Having just spent a considerable amount of time performing similar tests on the 13.3-inch (with an objective by Cauchoix) refractor at Markree Castle, County Sligo, first dedicated in 1834, the gentlemen astronomers stayed at Birr between October 29 and November 8, 1840. The guest astronomers were duly impressed with Lord Oxmantown’s newly erected 36-inch, declaring it “the most powerful telescope that has ever been constructed,” and even considered it superior to the late Sir William Herschel’s 48-inch behemoth. On all objects studies, which included the Moon, double stars, open stellar clusters and nebulae, the 36-inch showed its optical excellence. Indeed, according to Robinson (who became the first director of Armagh Observatory in 1823): “It [was] scarcely possible to preserve the necessary sobriety of language, of speaking of the Moon’s appearance with this instrument, which discovers a multitude of new objects at every point of its surface.” Robinson observed lunar features at a power of 900 diameters with the 36-inch reflector that were scarcely seen again for another 60 years, including the appearance of “two black parallel stripes in the bottom of Aristarchus,” which are now known to be depressions, and a series of “extremely minute craters” on the ridges of the crater Ptolemaeus. Robinson also observed M31  in Andromeda and the Great Nebula in Orion (M42) in the hope that the great telescope at Birr might resolve them into stars. Examination of the Dumbbell Nebula (M 27) in Vulpecula and the Ring Nebula (M57) in Lyra showed that they also remained wholly nebulous in the 36-inch. Alas, while he detected the telltale signs of individual stars on the edges of M31, the results were at best ambiguous and only served to strengthen his conviction that these objects were fundamentally non-stellar in origin. Star clusters such as M13 and M92 in Hercules were reportedly breathtaking at high powers through the same instrument. Lord Oxmantown was satisfied that he had indeed created a first-rate telescope that would contribute to scientific knowledge, and in the spirit of the age, warmly welcomed the finest observers across Europe to use the telescope for their researches: “Although the instrument and the laboratory where it was constructed are in the centre of Ireland,” he wrote, “the facilities of communication are such that those who desire further information can easily obtain it on the spot, and from their own estimate of the performance of the instrument.” His invitation was enthusiastically accepted, and in due course, distinguished scientists and observers of the ilk of Sirs John Herschel and James South, George

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Johnstone Stoney, William Lassell, James Nasmyth, Otto Struve, George Bidell Airy, Franz Friedrich Brünnow and George Gabriel Stokes all enjoyed time at the great telescopes designed by Lord Rosse. Yet, as soon as the 36-inch was completed, Oxmantown had made plans for an even greater instrument that would remove the still pervasive ambiguity concerning the nature of the celestial nebulae: I think that a speculum of 6 feet aperture could be made to bear a magnifying power more than sufficient to render the whole pencil of light, and that in favourable states of the atmosphere it would act efficiently, without having recourse to the expedient, which Newton pointed out at the last resort, that of observing from the vantage of a high mountain … an instrument even of the gigantic dimensions I have proposed might, I think, be commenced and completed within one year.

In making the 72-inch reflector a reality, Oxmantown was faced with a daunting task. A mirror twice as large would have four times the area of the smaller 36-inch and would be much more difficult to successfully cast, grind and polish. The reflector’s much greater weight would make it considerably more challenging to mount stably as well. As Robinson later pointed out in a paper presented in 1845, it was not possible to melt down the appropriate quantities of copper and tin in the crucible used to create the 36-inch speculum. Indeed, three such crucibles would be called for, each 24 feet in diameter and weighing half a ton apiece. Oxmantown had to construct a giant chimney-shaped furnace to accommodate the three crucibles. To achieve the necessary temperatures to create the liquid alloy, 2000 cubic feet of turf cut from a local peat bog had to be combusted for 10 h before the melt was ready. It must have been quite an apparition to catch sight of the thick yellow smoke billowing upwards from the giant furnace, its eerie yellow and orange glow being clearly visible for miles around. The cylindrical metal blank, weighing in at a whopping 4 tons, was successfully cast, but an accident of some unknown nature occurred one month into figuring the giant metal slab, with the result that a large crack rendered it useless. Undeterred, a plan was made to recast the same metal, and this time it was accomplished, though it was slightly thinner than the original, weighing a half ton less. The subsequent grinding and polishing phases also went well, and by April 13, 1842, the mirror was completed. In total, five castings were required to get two working 72-inch diameter mirrors (Fig. 9.3). Lord Rosse had to tread very carefully in considering the mounting for this giant telescope. The tube would be 58 feet long, and as a result, it would not be possible to mount it in the way the 36-inch telescope was. If a Herschelian-type mount were to be employed, the slightest breeze would set the giant telescope – which would weigh over 150 tons when completed – swinging wildly from side to side, not only making observations impossible but putting the lives of the observers and workmen operating the instrument in jeopardy. After much deliberation and consultation, Oxmantown settled on a mounting system set between two massive walls. These would be 70 feet long and 50 feet high, running parallel with the north-south line, so that celestial objects could only be examined as they crossed the local meridian. Indeed, for an object located on the celestial equator, the total viewing time would be restricted to an hour at most. But

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Fig. 9.3  The largest telescope of the 19th century, the Leviathan (72-inch aperture) of Parsonstown. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/William_Parsons%2C_3rd_ Earl_of_Rosse#/media/File:WilliamParsonsBigTelescope.jpg)

at least the great telescope would be able to view its target when it was highest in the sky and so less affected by atmospheric turbulence. Construction started on the Parsons demesne at the end of 1842 and continued right through 1843 and 1844. A cast iron joint – similar to a modern universal joint – occupied the base of the mount, and upon it was bolted an 8 foot wooden box that would carry the giant mirror. Around this was placed the telescope tubing, fashioned from inch-thick staves, and held in position by a series of iron clamp rings. The tube tapered down to 7 feet at its extremities, making it a rather odd, cigar shape. Movement in declination was undertaken via a series of thick metal cables fastened to the top of the telescope, and maneuvered by a system of elaborate pulleys. Right ascension (to and fro) motion was accomplished with a manually operated steering wheel. In addition to these course movements in both right ascension and declination, provision was made to allow fine adjustments in both axes to center the object under study. Oxmantown also had the presence of mind to install finely meshed screens under the telescope, so as to protect workers from the accidental fall of eyepieces and other items of equipment. The financial outlay of the Leviathan was very considerable – in excess of £12,000 in the currency of the day and a clear statement of the considerable wealth of its creator!

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Observing with the great telescope was never a solitary affair. Indeed, its routine use always required a well-trained team of operators, who had to follow precise verbal instructions from the astronomer assigned to it on any night. Nor was the telescope ever fitted with a finder telescope! Instead, Oxmantown employed a low power, wide-field ocular of his own design, with a magnification of 216 and possessing a generous true field of 31 arc minutes (just large enough to show the full Moon), to center objects that were to be studied. And while he had intended to install a clock drive to move the instrument in right ascension, in the end, this never came to fruition, neither under the third Earl’s watch or that of his son, the fourth Earl. After undertaking a series of mechanical trials over the winter of 1844, the instrument was deemed ready for operation in February 1845, when both Robinson and South were once again invited to Birr Castle to provide an assessment of its efficacy. Alas, the weather didn’t cooperate, and opportunities to test the Leviathan were few and far between. First light came for an hour or so on the evening of February 15, when the telescope was turned on Castor, a famous double star in the constellation of Gemini. To the delight of all in attendance, the system was easily and cleanly split, the components appearing more brilliant than any other telescope in existence. Next, the great light bucket was directed at M67, a small open cluster situated across the border in Cancer. Robinson and South reported that the faint stars in the cluster were magnificently rendered. Then the clouds rolled in again. And with further changes in the weather occurring over the next few of weeks, it was decided to remove the primary mirror for further polishing  – no mean task in itself, as it required the combined effort of 25 or 30 workmen! Although it is unquestionably the case that the 72-inch Leviathan of Parsonstown was very unwieldy by modern standards, Sir James South reported that he could uncap the telescope, have its position adjusted by the assistants on both axes and have a star centered for observing in about 8 min! Second light occurred on March 4, where a spell of settled weather made observations possible up until March 13. No opportunities were missed to turn the great telescope on a suite of double stars, open clusters and nebulae that hugged the meridian at that time. It was over this period that Robinson and South declared the instrument optically excellent and capable of doing first-class astronomical research. When George Airy attended the telescope, he reported an exquisite image of Saturn. That having been said, the images apparently suffered from some distortion when pointed at objects at lower altitude but were nearly perfect when pointed at objects higher up in the sky. This no doubt indicated that the mirror had probably lost precise collimation during the examination of low lying targets, something that Oxmantown was confident he could address. Later the same month, the telescope was officially inaugurated by Dean Peacock, head of the (Protestant) Church of Ireland, who is said to have walked through the giant tube, inspecting it from one end to the other while donning a top hat with a raised umbrella above his head. In the milder months that followed, the Leviathan was turned on the nebula listed as number 51 in Messier’s famous catalog (see the author’s previous chapter on Charles Messier). Located in Canes Venatici, it was examined and its spiral structure clearly

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Fig. 9.4  Drawing of the Whirlpool Galaxy by Rosse in 1845 using the Leviathan. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/William_Parsons%2C_3rd_Earl_of_Rosse#/ media/File:M51Sketch.jpg)

seen – a momentous discovery for sure, but one that was overshadowed by a spate of terrible events (Fig. 9.4). The summer of 1845 marked an atrocious turning point in the history of this small nation. By now, the potato famine was palpably showing its devastating effects (with 50% of the crop having been infected with blight), and the peasants who worked the land throughout the county were beginning to starve. Lord Rosse was by now a peer in the British House of Lords and still served as Lord Lieutenant and Colonel of Militia of Kings County. Admirably, though, he put the needs of his countrymen first, and after consulting with the British Prime Minister, Sir Robert Peel, and his panel of appointed scientific experts, provisions were made to import cheaply purchased maize and cornmeal from the New World, which helped somewhat but could not fully ameliorate the human disaster. It was not until January of 1848 that Lord Rosse would resume active research with the great telescope. But when it was uncapped after a three-year hiatus, the mirrors were found to have tarnished, owing to the excessively damp weather that characterized the worst of the famine years. And though a second mirror had by then been successfully cast, it had not been polished to the required degree. But by February 16 both specula were ready for action, and by month’s end, astronomical observations were in full swing once again. Indeed, the great telescope remained in active service for many years thereafter. It became the centerpiece of international

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Fig. 9.5  A 6-foot telescope, a 3-foot telescope and a castle. Watercolor by Henrietta Crompton. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Leviathan_of_Parsonstown#/ media/File:Birr_Castle_by_Henrietta_Crompton.jpg)

attention, and tourists flocked to see it from all around the world. It was all the more remarkable that its creator did it all off his own back, with no financial assistance from governments or monarchs, quite unlike the situation with Sir William Herschel (Fig. 9.5). According to research conducted by the late Sir Patrick Moore, the defining power of the Leviathan was called into question by a number of individuals, mostly casual observers, but affirmed by those who had been given the opportunity to observe with it on a regular basis. One such tyro is reported to have remarked: “They showed me something which they said was Saturn, and I believed them….” But the reader should note that such a monstrous telescope, with the huge aperture it possessed, was much more sensitive to atmospheric turbulence than instruments of much smaller aperture, particularly the equatorially mounted classical refractors, which by now were adorning the observatories across Europe and North America. Consider, if you will, the remarks of the distinguished Irish physicist and astronomer, George Johnstone Stoney (1826–1911), himself a native of the town of Birr, whose reputation as an observer was unquestioned and who carried out careful tests on the 72-inch instrument over an extended period of time (4 years to be precise, over the period 1848–1852): The test usually applied was the performance of the mirror on the star of the 8th or 9th magnitude, magnification 750. Such stars are bright in the great telescope. They are usually

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seen as balls of light, like small peas, violently boiling in consequence of the atmospheric disturbance. If the night is good there will be moments now and then when the atmospheric disturbance will abruptly seem to cease for a fraction of a second, and the star is seen for an instance as the telescope really presents it. It is by the opportunities of such moments that the performance of the telescope must be judged. With the best of your father’s* mirrors that I saw, the appearance at such opportunities was that of the light shining through a minute needle hole in a card placed in front of a flame. I think any practical astronomer will agree with me in the opinion that mirrors of 6 feet in diameter that bore the test bordered very closely indeed on theoretical perfection.

*Stoney is referring here to the third Earl of Rosse, but the communication was to his son, who succeeded to the title of fourth Earl by the time the scientific correspondence was published on April 2, 1878. There is really nothing new under the Sun. Then, as now, casual observations are not likely to reveal any great truth but rather have the greater potential to disseminate untruth. Indeed Moore, in his book, The Astronomy of Birr Castle, provides still more evidence that the mirrors made by the third Earl of Rosse were of high quality. In February of 1848, shortly after the Leviathan was dedicated, Romney Robinson described a fine night in which Jupiter presented with”a remarkable appearance …. full of faint striae running nearly parallel to them, and seemingly belonging to the brighter zones on each side.” And in 1889, a series of published drawings of Jupiter made by a later assistant of Lord Rosse, Dr. Otto Boeddicker, between 1881 and 1886, show that they compared well with modern instruments of the same size, according to the noted planetary observer Stanley Williams (discussed in a later chapter), who conducted such a study in 1935. Still more evidence of its optical quality can be gleaned from a discussion of the telescope in Henry C. King’s classic tome, The History of the Telescope, where he notes that the Leviathan was capable of resolving very tight double stars. On one occasion, Robinson, South and Lord Oxmantown managed a clean split of Gamma 2 Andromedae with a power of 828 diameters and a then separation of 0.5″. Such testimonies show that while the telescopes of Lord Rosse were not ‘planetary’ instruments in the traditional sense (they were seldom employed in this arena), they were more than capable of doing first-rate science. The enormous light-gathering power of the Leviathan (which was recently estimated to have the light gathering power of a state-of-the art 25-inch aluminized glass mirror by Dr. Wolfgang Steinicke) added to the tally of spiral nebulae. Indeed, by the end of 1850, a total of 14 such structures were positively identified by Lord Rosse and his astronomical assistants. These included M33, M31, M77, M95 and M99. It was even possible for Lord Rosse to begin to sub-classify these spiral nebulae into a variety of classes, including barred, diffuse and irregulars. He also suspected that many of the elliptical and lenticular nebulae the surveys showed up must be spiral also but that they were seen ‘edge on’ rather than ‘face on.’ The spiral nature also strongly suggested to him that their complex shapes could only be maintained by motion, although he recognized that making any such measurements was hopelessly beyond his means, as they were so far away (Fig. 9.6). One enduring mystery concerning the discovery of the spiral nebulae pertains to why the keen eye of Sir William Herschel was unable to detect them as such. It is

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Fig. 9.6  One of the original two mirrors used in the Leviathan. (Image courtesy Wiki Commons. https://en.wikipedia.org/wiki/Leviathan_of_Parsonstown#/media/File:Rosse_six_foot_telescope_ mirror.JPG)

most certainly true that the brighter spiral nebulae should have been visible in his largest telescope, the celebrated 40-foot reflector outfitted with a 49.5-inch primary speculum. One explanation, advanced by this author, may lie in Herschel’s decision to adopt his off axis (Herschelian) design, which, as we have learned, introduced some aberrations to the images that reduced the instrument’s defining power enough to render the faint and delicate spiral arms all but invisible. Evidence in support of this comes from Herschel’s failure to detect the E and F stars of the theta Orionis complex, as well as the fact that he almost invariably employed low powers with this instrument (much of his fine planetary work was conducted with a much smaller instrument, a conventional long focus Newtonian of 6.3-inch aperture). Yet another possibility is that Herschel may have observed such objects when his mirrors were in a more advanced state of tarnishing. In a work published by William F. Denning (discussed in a later chapter), we are made aware that slight tarnishing (of a silver substrate) could often be useful in improving planetary images, acting in much the same way as a modern neutral density filter, which can reduce glare and improve contrast. But this would not be the case with deep sky objects, where even slight tarnishing will appreciably reduce the so-called “space penetrating power,” as Herschel referred to it, helping to explain why he did not see the spiral structures that were so obvious to Lord Rosse and his assistants. That said, without some form of reconstructive experimentation, we shall probably never know the precise reasons for this anomaly. One of the most important questions still to be resolved (excuse the pun) was the nature of nebulae in general. Sir John Herschel had formed the opinion that all

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nebulae would eventually be resolved into stars, but Lord Rosse was an agnostic in this matter. Telescopic scrutiny of many objects with the Leviathan, including M1 (the Crab Nebula, as coined by Lord Rosse himself), M27, M56 and M97 did not show stellar constituents, so the jury was still out concerning this question. But there were always nagging doubts that the mirror might not have been gathering the amount of light it was capable of due to rapid tarnishing in the humid, southern Irish climate. Concerning this possibility, Lord Rosse wrote: We have had perhaps two or three specula as perfect as the first one; but the mass of observations has been made with specula considerably inferior to it, and, I am sorry to say, very often not as bright as they should have been …..While the telescope was in constant use in all weathers, it would have been a hopeless task to attempt to keep it in a state fit for the resolution of nebulae, and the attempt was not made. I may, perhaps, mention that with the 3 feet speculum in fine order I have often detected resolvability when there was no trace of it with the 6 feet speculum in its ordinary working state.

That said, Lord Rosse’s caution concerning the universality of stellar nebulae was vindicated just over two decades later, when in 1864 William Huggins employed spectroscopy to show that some nebulae were distinctly different from those of stars. As discussed previously, Lord Rosse did not employ a finder with the telescope, relying instead on the 31 arc–minute field in the ‘low power’ setting. Oculars of various focal lengths were placed on an elegant sliding mechanism so that the observer could move from low to high power with little or no delay. The Leviathan was also fitted with a micrometer, the proper operation of which was a necessity for making the elaborate drawings of deep sky objects with their correct scale. Indeed, George Bindon Stoney became adept at measuring the sizes of various spiral nebulae using a home-made micrometer at Parsonstown. Records show that the instrument could be used about 60 nights per year, but in retrospect, it seems rather odd that Lord Rosse would choose to erect the great telescope so close to the Bog of Allen (from which the turf was derived to power the furnaces for the molten optical metal), which encouraged fog banks to form on still evenings, further reducing its utility. Indeed, the archives at Birr Castle reveal that the great telescope was seldom used after 11 p. m. at night owing to the misty fogs that would rise up as if by magic from its boggy hinterland. But at least these observations served to warn later generations of giant telescope makers to pay closer attention to the observing site before committing to some ambitious project. Indeed, nearly all later telescopes of grand estate were erected upon sites that were carefully field tested prior to the commencement of any building. The great telescope and the opulent milieu in which it was erected became a kind of Mecca of learning for two generations of astronomers, many of whom made their astronomical debuts observing with the great telescope. In 1852, Oxmantown hosted a meeting of the British Lunar Committee on the grounds of Birr Castle. As a general rule, Lord Rosse employed many young observers (no doubt owing to their enthusiasm for astronomical work and keen vision), who served at the telescope for a number of years before moving on to other observatories in order to further their careers. For example, Robinson served as the first director of Armagh Observatory

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Fig. 9.7  Professor Sir Robert S. Ball (1840– 1913), distinguished Victorian astronomer and popularizer of astronomy. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Robert_Stawell_Ball. jpg)

(a post he held until he was 90!), and a young Sir Robert Stawell Ball (Fig. 9.7), who served as an astronomical assistant at Parsonstown between 1865 and 1867, as well as an academic tutor to Lord Rosse’s children, who became a future Astronomer Royal for Ireland (based at Dunsink Observatory, Dublin, between 1874 and 1892), before being appointed to the prestigious position of Lowdean Professor of Astronomy at Cambridge University in 1893. Of Lord Rosse, Sir Robert graciously observed, “personally and socially, [he] endeared himself to all with whom he came in contact.” Lord Oxmantown, the third Earl, maintained an active role as an observer until failing health in the early 1860’s forced him to give up routine astronomical work, entrusting all research to the assistants whom he assiduously trained. In the summer of 1867, on the advice of his physicians, the aging peer retired to the seaside residence of Monkstown, overlooking Dublin Bay, in the hope that the fresh, maritime air would improve his condition. But it was to no avail. He passed away peacefully on October 31 of the same year. It was at about the same time that Lord Rosse’s eldest son (1840–1908), the fourth Earl, began to take on more of an active role in his father’s work. Born and raised in Birr, he was educated at Trinity College in Dublin, and Oxford University, before returning to Ireland to serve in various high-profile roles in the administration of the province. Though largely considered to be overshadowed by the achievements of his father, Lawrence Parsons (Fig. 9.8) embraced the new technologies that were coming to the fore, having first experimented with a newly erected 18-inch

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Fig. 9.8 Lawrence Parsons, fourth Earl of Rosse (1840–1908). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Lawrence_ Parsons%2C_4th_Earl_of_ Rosse#/media/ File:Lawrence_Parsons. jpg)

reflector of 10 feet focus, which was ingeniously powered by a water wheel in 1866. In the years that followed, the fourth Earl managed to construct partially successful clock drives for both the 36-inch and 72-inch telescopes. The provision of crude clock drives on the two great telescopes enabled more sophisticated science to be performed. For example, crude spectroscopic analyses of a variety of deep sky objects was carried out. Much of this important work was performed by a young Dane, John Louis Emil Dreyer (1852–1926), who had put down roots by marrying a lassie from County Limerick, serving as assistant astronomer at Birr between 1874 and 1878. Dreyer demonstrated that all of the spectra obtained on the spiral nebulae were shown to be stellar in character, while all those obtained from the planetary nebulae showed quite distinctive line spectra, further advancing the notion that there were fundamental differences in the nature of nebulae. Dreyer used the Leviathan to add a considerable number of newly discovered nebulae to the tally already discovered by his distinguished predecessors (particularly Messier and the Herschels). Many of these new objects were recorded in a catalog compiled by the fourth Earl covering the three decades between 1848 and 1878. Another notable discovery was made by the English astronomer Ralph Copeland (1837–1905), who served as assistant astronomer at Birr between 1871 and 1876, and used the enormous light-gathering power of the Leviathan to discover 35 new NGC objects, most famous of which is a grouping of seven large galaxies in Leo – Copeland’s Septet, as it is known today – that include NGC 3745, 3746, 3748, 3750, 3751, 3753 and 3754.

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The fourth Earl of Rosse is perhaps best known for his work in determining the surface temperature of the sunlit face of the Moon. For decades, astronomers such as Piazzi Smyth and Macedonio Melloni (inventor of the first infrared thermopile in 1831, which transduced thermal energy into electrical energy) had wondered whether the Moon would have an equable temperature like that of Earth, and to this end he had carried out the first crude experiments in its determination, with results that turned out to be mostly inconclusive. Determining the temperature of the Moon is far from trivial, however, as a moment’s reflection (excuse the pun once again) will reveal. Lord Rosse correctly concluded that the contribution of thermal energy from lunar volcanism was negligible. That leaves two principal sources of heat. First, there will be that which is reflected. This will be largely independent of the temperature of the Moon’s surface, but rather will depend only upon its power of reflection (its albedo). The second contributor to lunar heat is that which it emits as a consequence of natural heat, which is mainly, but not entirely, due to solar irradiance. The amount of this heat will depend upon the temperature of the Moon’s surface and its radiating power. Though the thermopile could not readily distinguish between these two sources of heat, Lord Rosse realized that they would vary differently in accordance with the development of the lunar phase, with the former increasing steadily from thin crescent and reaching a maximum at full Moon, while the latter ought to lag behind the former, as a consequence of the time it takes for the surface to heat up (in much the same way as daytime summer temperatures reach their maximum several hours after noon). Thus, this ‘dark’ (infrared) heat ought to be at its maximum after full Moon. Lord Rosse began such measurements using the 36-inch reflector in 1868, and the careful work continued for several years. His first estimates showed that the lunar surface temperature near the equator could reach 500° Fahrenheit (260° C), but with subsequent refinements made by his fellow physicists, he later revised this down to just over 200° Fahrenheit (or about the boiling point of water at sea level). The latter measure agrees well with the modern accepted maximum value of 253° Fahrenheit. Of course, the temperatures arrived at by Lord Rosse referred to the equator, in the middle of a long lunar day. Naturally, the further away from the equator one moves, the cooler the surface becomes. He performed similar experiments during a lunar eclipse, when its surface is cut off from all direct sunlight. Indeed, he was able to monitor a rapid drop in lunar surface temperature as a ‘wave of cold’ moved across its surface. What is more, he managed to record enormous temperature swings in the course of an hour. This provided further proof that the Moon is an airless world, incapable of holding onto heat as it moves from direct sunlight into darkness. The interested reader may see this magnificent instrument in the Science Museum at Birr Castle today, complete with the thermopile mounted at prime focus. By the 1880s, the Leviathan was most definitely showing its age, and many astronomers felt that its best days were well behind it. Indeed, from the late ­nineteenth century onwards the 72-inch was mostly used in sporadic observations of

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interesting objects. For example, on the night of September 17, 1877, Lord Rosse was able to confirm the existence of the tiny Martian satellites, Deimos and Phobos, discovered by Professor Asaph Hall just a few short months before, using the great Washington refractor. The last and longest serving assistant assigned to the Leviathan was the aforementioned Dr. Boeddicker, who concerned himself with detailed visual observations of the northern Milky Way. This culminated with an extraordinarily detailed drawing of the vast stellar archipelagos within its confines, taking him no less than 5 years to complete, beginning in 1885 and coming to an end in 1890. Doubtless, it was a work of outstanding artistic beauty, but alas, photography was now all the rage, and as a consequence, the significance of Boeddicker’s work was of questionable scientific value. And while the venerable 36-inch was now equatorially mounted with a smoothly operating clock drive, in the hope that it might at least be used as an astrograph, the declining relevance of the antiquated Leviathan weighed heavy on the fourth Earl’s mind: “Can the pencil of the draughtsman be any longer profitably employed upon nebulae as seen through the 6 foot reflector when photography, to say the least, follows so closely on his heels?” The metal mirrors making up the telescopes of the Rosse estate were possibly as good as they could be, but new technology made them living dinosaurs. In particular, the advent of much lighter silver on glass mirrors rendered the construction of large, observatory class reflectors much easier to fashion, owing to their vastly reduced mass and higher reflectivity. In addition to this, glass substrates, with their lower thermal coefficients of expansion (and, to a lesser degree, their higher specific heat capacities) than the old speculum metals rendered them considerably less sensitive to small changes in temperature, allowing more stable images to be maintained in the course of a night’s work. Lord Rosse passed away on August 30, 1908, and with him all work with the Leviathan of Parsonstown ceased. With his brothers becoming the executors of his estate, the great telescope was dismantled. In 1912, the 6-foot mirror was removed and dispatched to the Science Museum in London for preservation. The 36-inch was also left idle. Dr. Boeddicker remained in the employ of the fifth Earl, though not, it seems, in a scientific capacity. He was entrusted with gathering together the historical archives of the family. And when the First World War broke out in 1914, Boeddicker, a native of Germany, was considered an enemy of the state (which was still under British rule) and was forced to return to his own country. He died aged 84 in 1937, under Hitler’s Third Reich. The next decade of Irish history proved very turbulent, with the result that the Rosse family had to leave the castle for extended periods of time. By the time the political climate settled down in the late 1920s, the great infrastructures that once boasted the largest telescopes on the face of God’s Earth were in a very sad state of dilapidation, though according to Sir Charles Parson, the 36-inch was nearly intact as late as 1927. That said, its whereabouts today is unknown, although curiously, a small piece of the original metal making up the 36-inch mirror was found by ­accident in the castle grounds back in May 1991 and which is now also displayed at the Science Museum at Birr.

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Fig. 9.9  The reconstructed Leviathan at Birr Castle. (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/Leviathan_of_Parsonstown#/media/File:Greate_Telescope,_Birr,_ Offaly_2.jpg)

A final twist in the story of the Leviathan occurred after a TV program, lecture, and book by the late Sir Patrick Moore appeared on the great telescope in the 1970s. This resulted in a renewed interest in the 72-inch telescope, with the restoration of its wooden tube between 1971 and 1975, and soon it became a tourist attraction. But it was not before the 1990s that plans to actually rebuild the telescope came to fruition. In 1994, the retired structural engineer and amateur astronomer, Michael Tubridy, was commissioned to research and re-design the Rosse Leviathan. Unfortunately, the original plans were lost, and so it took a considerable amount of detective work that included re-examining the remains of the telescope, together with old observing logs and contemporary photographs taken by Lady Mary Rosse, wife of the 3rd Earl. Reconstruction work lasted from early 1996 until the beginning of 1997. It had been planned to include a working mirror, but owing to budget constraints, this had to be left for a separate project. The new mirror was installed in 1999. Unlike the original speculum metal alloy, and in a historically respectful departure from modern aluminum – or silver-coated glass mirrors, the replica was cast from solid aluminum, thus acting as a compromise between authenticity and utility in astronomical observation (Fig. 9.9). The great technical achievements of the Rosse family, their friendship to the people of Ireland, as well as to the wider international astronomical community, will not easily be erased from memory. Once the brain and glory of all that was held dear in astronomical inquiry, their telescopes continue to be remembered in the mind’s eye as emblems of the indefatigable spirit of the human imagination – to peer farther into space than anyone had ever peered before, to bring the heavenly creation closer to Earth, as well as to understand something more of its mysteries. And we’ve been doing that ever since!

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Sources Ball, R.S.: The Story of the Heavens. Casell, London (1893) Bell, L. The Telescope (1922). Hard Press Publishing, (2013) Denning, W.  F., Telescopic Work for Starlight Evenings (1891). Hard Press Publishing (2013) modern re-print of the 1891 classic. Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Hoskins, M.: The Leviathan of Parsonstown: ambitions and achievements. J.  Hist. Astron. 31, 57–70 (2002) King, H.C.: The History of the Telescope. Dover, Mineola (1955) Mollan, C.: William Parsons, 3rd Earl of Rosse: Astronomy and the Castle in Nineteenth-century Ireland (Royal Dublin Society  – Science and Irish Culture). Manchester University Press, Manchester (2014) Moore, P.: The Astronomy of Birr Castle. Quack Books, York (1992) More about Birr Castle for the Astronomical Tourist. http://birrcastle.com/ Observations on the Nebulæ, by the Earl of Rosse, 1850. http://rstl.royalsocietypublishing.org/ content/140/499.full.pdf+html?sid=b88c8dc8-0e27-421b-b211-659c970c0d35 Professor Paul Callanan of University College Cork explains the significance of Lord Rosse’s Leviathan. Some History of Birr, Ireland. https://www.youtube.com/watch?v=dNG5JgRL3xM Tobin, W., Holberg, J.B.: A newly discovered accurate early drawing of M51, the Whirlpool Nebula. J. Astron. Hist Herit. 11, 107–115 (2008)

Chapter 10

The Astronomical Adventures of William Lassell

It is a curious fact that beer has facilitated the emergence of some of the key figures in the history of astronomy. For example, in a previous chapter, we have already covered the saga of Johannes Hevelius of Danzig in the late seventeenth century, whose fortune came through brewing. And it was also true of William Lassell (born June 18, 1799), the son of a timber merchant hailing from Moor Lane in Bolton, Lancashire, in England (Fig. 10.1). After receiving a rudimentary education at Bolton Day School and, for a short spell, at Rochdale Dissenting Academy, the death of Lassell’s father in William’s mid-teens forced him to seek an apprenticeship with a brewing company in Liverpool, which he faithfully served between 1814 and 1821. After he had fully immersed himself in all aspects of the business, he found his own brewing company in 1825, securing him an early fortune from which he could pursue his passion for building and using large telescopes. In his mid-twenties Lassell got engaged and married Maria King, the brothers of whom were all keen amateur astronomers. Following in the footsteps of the work of the Herschels, Lassell immersed himself in the practice of fashioning high-quality specula for use in astronomical telescopes. Indeed, his first success came at the tender age of 21, when he made both Newtonian and Gregorian instruments, both of which had about 7 inches of aperture. As well as the traditional ratios of copper to tin, Lassell also added various amounts of arsenic but later found it conferred little or nothing of benefit to either the brilliancy or longevity of the resulting mirrors. Nevertheless he was clearly unimpressed by the mounting arrangements used by the Herschels, which severely curtailed their productivity in the field. On the other hand, Lassell became deeply impressed by the elegance of the equatorial mount adopted by the German optician and telescope maker Joseph von Fraunhofer who, by 1824, displayed his newest brainchild, the 9.6-inch refractor for the Dorpat Observatory. It was this state -of -the- art mounting system that led Lassell to create his own equatorially mounted reflector, which he completed in 1833. This Newtonian had an aperture of 9 inches with a focal length of 112 inches

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Fig. 10.1 The distinguished astronomer and telescope maker, William Lassell (1799– 1880). (Image courtesy of Wiki Commons. https:// en.wikipedia.org/wiki/ File:William_Lassell.jpg)

(f/12.5) and was erected at his private observatory at Starfield in West Derby, Greater Liverpool. Unlike his predecessors, Lassell went to great lengths to maintain the rigidity of the components in the optical train, which ensured precise collimation wherever the instrument was pointed at the sky. The instrument was mounted inside an iron box, which itself was securely bolted to a cast iron cone. With such an instrument Lassell discovered the sixth member of the Theta Orionis (a.k.a. the Trapezium) complex at the heart of the Great Nebula in Orion. With the same instrument, employing a power of 450 diameters, Lassell was able to show that Saturn’s exterior ring was in fact made up of two distinct annuli – an observation that was also confirmed by the Reverend William Rutter Dawes with his large Cooke refractor. Indeed, many of the exacting optical tests used by Lassell in assessing the quality of his specula were the subject of some of Dawes’ writings during the time. The functionality of the 9-inch Newtonian proved a big hit with many members of the Royal Society, who examined the instrument in 1839, for which he was made a Fellow, and which is described in detail in the twelfth volume of the society’s Memoirs of 1842. And though the optical tube assembly of the ‘scope was fashioned from cast iron rivets, making it very heavy, all the moving parts of the mount were cushioned on ball bearings that made the instrument easy to push with just one finger! Indeed, though some of his contemporaries were loathsome to admit it, Lassell’s 9-inch f/12.5 was probably the finest high-resolution telescope in existence in

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England in the mid-nineteenth century, shattering the myth that the refracting telescope could alone yield fine planetary images. Indeed, Lassell rebuked many contemporary mirror makers for over polishing their specula to a high luster, pointing out that the attainment of a highly accurate and smooth figure was more important in the discernment of fine details. In addition, Lassell made provision for the optical tube to be rotated on specially designed rollers so that maximum comfort at the eyepiece could be maintained. It was with the same instrument that Lassell quickly established himself as one of the best planetary observers of his day. Indeed the detailed working of the same telescope was the subject of an important paper submitted to the RAS in 1842. Allan Chapman, distinguished historian of science at the University of Oxford, summed up Lassell’s philosophy thus: “I believe that William Lassell’s significance derives from the fact that he was the man who, more than any other, carried on the physical astronomy tradition from Herschel, and recognized the role of the large reflecting telescope within it.” Aperture fever was soon to beset Lassell, however, and this may have come about from his visit to Parsonstown (modern Birr), Ireland, in 1844, where he inspected Lord Rosse’s optical workshops and witnessed the erection of the giant 72-inch mirror that formed the heart of the Leviathan. Upon his return from Parsonstown, Lassell embarked on creating his own monster telescope – a 2-foot reflector with a focal length of 20 feet (f/10). To this end, he made a steam-powered machine for grinding and polishing the mirror, but departed somewhat from the techniques hitherto employed by Rosse and many of his contemporaries. Instead of the straight strokes, Lassell introduced more natural, circular strokes to his polishing machine, which more closely resembled those made by human hands. Needless to say, the mirror was a great success when it was completed in 1845. Lassell also benefitted greatly from the input of the brilliant Scottish engineer and amateur telescope maker James Nasmyth (1808–1890), who ran a successful foundry at Patricroft, Salford. Originally, Lassell had learned how to make a grinding machine to create his telescope mirrors from Lord Rosse in Ireland but found that they were simply not as good as could be produced by the work of his own hands. This is where Nasmyth (Fig. 10.2) proved to be of incalculable benefit, as he was able to redesign Lassell’s grinding machines so that they produced strokes much more akin to those derived from human effort. The resulting collaboration between these two men resulted in the speculum metal telescope reaching its zenith in terms of optical refinement. Indeed, the two were to remain firm friends for the rest of their lives. The mirror alone for this giant telescope weighed in at a whopping 370 pounds and, when mounted inside the completed 30-foot-long iron tube, had a total mass exceeding 2 tons. The giant Newtonian was mounted between two iron piers weighing collectively about 5.5 tons, but like his elegant 9-inch instrument, the 24-inch could be moved with equal grace. Remarkably, the telescope had no clock drive. It was instead powered by an assistant who operated a winch handle. Intriguingly, members of Liverpool Astronomical Society made a full-scale reproduction of this 10-inch telescope in the mid-1990s, where it was shown to produce razor-sharp images that were at or above the diffraction limit for such an instrument.

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Fig. 10.2  The great Scots engineer and amateur astronomer James Nasmyth (1808–1890). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ James_Nasmyth#/media/ File:James_nasmyth.jpg)

And it wasn’t long before Lassell made his first important discovery with the 2-foot equatorial at Liverpool, the icy satellite Triton, when he was observing the newly discovered planet Neptune about a fortnight after its first unveiling. Here is a retelling of the event as related by the nineteenth century Irish historian of astronomy, Agnes M. Clerke, in her Popular History of Astronomy During the Nineteenth Century: The beautiful instrument afforded to its maker, October 10, 1846, a cursory view of a Neptunian attendant. But the planet was then approaching the sun, and it was not until the following July that the observations could be verified, which it was completely, first by Lassell himself, and somewhat later by Otto Struve and Bond of Cambridge (U. S.). When it is considered that this remote object shines by reflecting sunlight reduced by its distance to 1/900th of the intensity with which it illuminates our moon, the fact of its visibility, even in the most perfect telescopes, is a somewhat surprising one.

Further observations revealed Triton’s retrograde motion, that is, it orbits the planet in the opposite direction to which the planet itself rotates, a peculiarity it shares with some of the smaller satellites of Uranus, and possibly indicative of their gravitational capture after the original systems formed from the solar nebula (Fig. 10.3). In recent years, an interesting communication by the British writer and amateur astronomer Richard M. Baum suggests that Lassell lost out on a chance to join the British search for Neptune and may have gone on to be the first to see the ice giant. Although this is probably more wishful thinking than anything else, there are no surviving records by Lassell to suggest that he ever expressed the slightest degree of bitterness in losing out to Johann Galle at the Berlin Observatory.

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Fig. 10.3  Schematic drawing of Lassell’s observatory featuring the equatorially mounted 9-inch Newtonian. (Image courtesy of Mike Oates. Used with permission)

Lassell’s prestige with the 2-foot telescope went from strength to strength in the months and years ahead. In 1848, while carrying out routine observations of the Saturnian system, Lassell spied a 13th magnitude ‘star’ very near the plane of the planet’s rings. As it turned out, George and William Bond, employing the 15-inch Merz refractor at Harvard College, had spied this new object just two nights before, on September 16, 1848, but had not reported it. This was the new Saturnian satellite, Hyperion, and Lassell was credited with its co-discovery. But more singular success followed fast on the heels of Hyperion, when Lassell used his large reflecting tele-

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scope to make a new search for faint satellites of Uranus. And sure enough, two new worlds, Umbriel and Ariel, were sighted on the evening of October 24, 1851, bringing its tally of moons to four. (The other two, Titania and Oberon, were discovered by William Herschel back in 1787.) The magnifications he employed for this discovery were 614× and 750× (see the Monthly Notices of the Royal Astronomical Society (MNRAS), Vol. 12, p. 15). That these new Uranian satellites, each about twice as faint as Oberon or Titania, were not picked up by Herschel gave nineteenth century historians cause for investigation. Agnes M. Clerke, for example, phrased it this way: In all probability they [the new satellites] were first time seen, for although Professor Holden made out a plausible case in favor of the fitful visibility to Herschel of each of them in turn, Lassell’s argument that the glare of the planet in Herschel’s great specula must have rendered almost impossible the perception of objects so minute and so close to its disc, appears tolerably decisive to the contrary.

Whatever the verdict concerning the new moons of Uranus, Clerke does concede that “their disclosure is still reckoned amongst the very highest proofs of instrumental power and perfection.” This author would broadly agree with Clerke, as the historical evidence suggests that while Triton is not especially difficult with a 10-inch or larger modern telescope, the fainter satellites of Uranus  – Ariel and Umbriel  – are not generally reported to be visible in any instrument smaller than about 16 inches. The reader will note that the satellites were confirmed to exist using the Harvard 15 Merz equatorial. The discovery of the two new satellites of Uranus brought considerable fame to Mr. Lassell, and many of Europe’s most prestigious astronomers paid him a visit. Indeed, on her official visit to Liverpool, Queen Victoria is reputed to have exclusively requested an audience with the astronomer. Indeed, in a totally unprecedented move that broke with convention, rumor has it that Her Majesty rose from her seat as soon as he entered the room! Lassell also used the 20-foot equatorial to study the giant planet, Jupiter, and its satellite system at Liverpool. His drawings of the Jovian disk reveal a wealth of surface detail and the Galilean satellites as hard disks. In one communication to the MNRAS dated March 27, 1850, Lassell discloses that he was using the full aperture (24 inches) on Jupiter much of the time, employing a power of 430 diameters. Lassell also divulges that while he had used modest aperture stops when observing the giant planet, no meaningful improvements were seen. “I tried 22″ and 20″ aperture, but there was no improvement in definition,” Lassell reported. Lassell built a long focus 3-inch speculum telescope that was mounted as a finder on the side of the main instrument. Gerard Gilligan, secretary of the Society for the History of Astronomy, had the chance to test it out on Saturn. “I can remember that this original mirror,” he writes, “was placed inside the replica telescope tube for the 150th celebrations, but that it slipped down the tube and was out of alignment, however we also attached and used the original speculum mirror 3-inch finder from the 24-inch telescope. On Saturn the image was clear but gave an orange tinge, with the planet above 20° in elevation. You could argue that this Orange coloration was due to sky conditions at the time (October 1996). (Fig. 10.4)”.

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Fig. 10.4 Project members examine the 3-inch speculum telescope Lassell used as a finder on the original 24-inch instrument. (Image courtesy of Gerard Gilligan. Used with permission)

As a veteran observer of the outer planets, Lassell was becoming increasingly conscious of the smog belched out by the private homes and industries of Liverpool, and how it was having an adverse effect on his observations. In addition, the damp climate would most assuredly cause his quality speculum mirrors to tarnish more quickly than in drier climes. Being a man of considerable means, Lassell decided to move his great telescope and himself south to the Mediterranean island of Malta in the autumn of 1852. Here, Lassell and his assistant, the German astronomer Albert Marth (1828–1897), set up their observing station at St. John Cavialer, Valletta, a fortress city “built by gentlemen for gentlemen.” It was hoped that the telescope would endure better conditions there, allowing him to extend his hunt for faint satellites of the outer planets and continue his study of selected deep sky objects. And, to some degree, the plan worked. By January 1853, Lassell had re-observed all four satellites of Uranus with the 24-inch and had convinced himself that “he [Saturn] has no other satellites than these four.” He was almost right, for it would take the best part of another century before a fifth satellite of Uranus, Miranda, would be discovered by Gerard P. Kuiper using photographs garnered from a much grander telescope; the 82-inch reflector atop Mt. Locke, Texas. Lassell’s earliest forays in telescopic astronomy on the island of Malta began in November 1852 and continued through to January 1854, when he turned the 20-foot equatorial at Valletta on the Great Nebula in Orion. The work, published in Volume 23 of the Memoirs of the Royal Astronomical Society, show that he studied the Orion Nebula (Messier 42) in unprecedented detail. In this report, Lassell noted the mag-

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Fig. 10.5  The original 24-inch speculum mirror used by Lassell. (Image courtesy of Gerard Gilligan. Used with permission)

nifications he used to study the various stellar bodies within its confines, 167 and 297× most commonly. He notes that at these powers he had never seen this deep sky object look so magnificent! He even tried 1,018× in order to establish whether the nebulosity would resolve into stars, but his results were negative. “The whole aspect,” he wrote, “is one of a number of masses of fleecy cloud, thin at the edges, and packed one behind another, appearing to be a deep stratum of successive layers of nebulous substance.” Lassell also described the visual appearance of the nebula as “pea green,” which appeared “very striking” to him. In the same publication, Lassell described the appearance of Rigel, the brilliant white luminary of the Celestial Hunter. “With this power [i.e., 1,018×],” he continues, “I turned to the neighboring star Rigel, which was admirably shown, the most striking feature, perhaps, being the small star accompanying it was exhibited by a beautifully neat round disk, circumscribed by a single hair-like ring most symmetrically formed.” (Figs. 10.5 and 10.6). What a wonderful revelation! How great it is to study the writings of our historical forebears! As any observer worth his or her salt will readily tell you, the companion to Rigel is often best seen in small apertures that are less affected by atmospheric turbulence, but here in these near idyllic conditions, Lassell described a sensibly perfect image in a 0.6-m aperture speculum metal telescope! This provides still more evidence that large apertures do indeed provide excellent views when conditions cooperate (a brute fact apparently lost to a new breed of contemporary amateurs), but they also bear testimony to the quality of the telescope he had built. At f/10, the aberrations that can plague faster ‘scopes were pretty much non-­existent, and this neatly explains why he was getting a perfect Fraunhofer diffraction ring surrounding the Airy disk of the secondary star at such enormous powers! (Fig. 10.7).

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Fig. 10.6  A modern reproduction of Lassell’s 24-inch speculum telescope, built by members of the Liverpool Astronomical Society. (Image courtesy of Mike Oates. Used with permission.)

Fig. 10.7  A drawing of Saturn made by Lassell employing the 20-foot telescope in September 1851. (Image courtesy of Mike Oates. Used with permission.)

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Fig. 10.8  The Orion Nebula painting, from observations made at Valletta, Malta, with the 20-foot equatorial, c. 1852/3. (Image courtesy of Mike Oates. Used with permission)

In another publication in the Memoirs (Volume 16), dated to the period 1855 to 1856, Lassell resumed his observations of Saturn, employing powers of between 430 and 565 diameters, which is a respectable ballpark to use on this planetary target with such an instrument. The same document shows that, on nights of less than perfect seeing, he would stop the instrument down to 20 inches, which often seemed to improve things somewhat. All this having been said, he vividly described the beautiful and variegated hues of the planet’s elaborate band patterns; descriptions that really only comport with the experience enjoyed in a large aperture telescope under favorable seeing conditions (Fig. 10.8). It was these kinds of observations, conducted exclusively with the 24-inch f/10 speculum, which firmly convinced Lassell that bigger ought to be better again. And so, he began to think about an even larger instrument (wouldn’t you?), fully twice the size of the one he had been using so productively in Malta these last few years. Enter the 48-inch! Work on the 48-inch speculum began back in Liverpool in the late 1850s, and again Lassell entrusted the help of his friend, James Nasmyth. Casting, figuring and polishing went well, and by 1859 he had erected the new telescope near his Liverpudlian villa. He also made a duplicate mirror of this size, which would be used once the other had become tarnished. The parabolic mirror had a focal length of 37.6 feet (f/9.4) and was mounted in Newtonian configuration inside an open iron tube. Remarkably, the enormous metal mirror was only 4.5 inches thick! In Volume 36 of the 1867 Memoirs, Lassell provided more details of the new telescope: There is no roof or covering over the telescope, but the observers are protected by being placed in one or other of the storeys of a tower, which affords a means of getting conveniently at the eyepiece, which, when the telescope points to the zenith, is about 39 feet from the ground. A staircase within the tower leads to the different storeys, which are about 4 feet and 6 inches square, and afford abundant room for papers, micrometers, eyepieces, lamps, and other small apparatus required; beside furnishing to the observer a most grateful shel-

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Fig. 10.9  William Lassell’s great 48-inch equatorial reflector. (Image courtesy of Mike Oates. Used with permission) ter from the dew, and occasionally from the inclement wind. During observation, however the size of the storey in use becomes practically much larger, by the opening of the folding doors and letting down the platform, as shown in the engraving; the available space being then about 6 feet 9 by 4 feet and 6 inches. The tower is carried round on a circular railway, and has besides, a revolution on its axis, and a radial motion to and from the telescope: so that at most altitudes and hour-angles the eyepiece is easily accessible. It has been usual, however, for the most obvious reasons, to observe within three hours of the meridian, east or west.

The tower housing the telescope was also well equipped with eyepieces, micrometers, maps, writing paper and lamps, much like any other observatory. Stairs allowed him to climb to any level and maintain a reasonably comfortable position while making his observations. Like his smaller 20-foot speculum, the 48-inch was also shipped off to the pellucid skies of Valletta, Malta, to avail of better seeing conditions than those served up in his native England. But his records show that while the instrument did enjoy many good nights of seeing, allowing productive work to continue, the winters proved just as wet as those he left behind. Indeed, sometimes weeks would go by without a single observation being recorded! (Fig. 10.9). Larger telescopes had advantages and disadvantages, and Mr. Lassell was honest about some of their shortcomings. He noted, for example, that the larger telescope was more severely affected by atmospheric turbulence and that the additional light-­

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gathering power of super large telescopes often produced images that were too bright, especially when focused on planets. Indeed, he noted that the additional glare from Saturn and Uranus hampered his ongoing visual searches for additional satellites. But he also noted that in periods of unusual atmospheric quietude, larger apertures showed their superiority to smaller instruments. Some wonderful insights were provided by Lassell in a Memoirs communication, Volume 36, entitled, Miscellaneous Observations with the Four-foot Equatoreal at Malta, dated November 6, 1867, which covered his observing records from the year 1862 through 1865. These show that he used the 48-inch to observe the bright planet Venus, which appeared tack sharp in the great telescope at 265 diameters and that “I had never seen the planet so well.” He continued to observe Uranus and Saturn, the rings of the latter world he observed edge on. He measured the angular diameters of both Uranus and Neptune to high precision. But the same document shows that the great 4-foot speculum was used to observe a great many nebulae (some of which were brand-new discoveries) at high powers from about 250 right through to over 1000 diameters (especially for the minute planetary nebulae). But what is perhaps most interesting is his recording of double star targets: September 27. The power being fine I turned the telescope on Delta Cygni, power 466. With full aperture and this power there are certainly a good many rays round the bright star, but the small one is conspicuous among them all; constantly and steadily visible. The companion is much redder and duller in colour than its primary, and is separated from it a full diameter of the large star. With 760 I am forcibly reminded of the appearance of Epsilon Bootis in the two foot equatorial. I daresay the surrounding light would be somewhat diminished by cutting the aperture to 45 inches; but as it is, it is to me an unrivalled view. With this power the separation is nearly 11/2 diameter. The hardness and roundness of the disks in this fine atmosphere are strikingly pleasing; I was never more struck with the conviction how necessary a pure and tranquil sky is to the just performance of a very large telescope.

And there’s more. Think Sirius B would be beyond the pale for this giant telescope, as some may have led you to believe? Think again! For in the same communication he writes: 1865 Feb 4: *Clark’s Comes (secondary), very plain, 11th magnitude; but is too windy to measure. March 24: The image strikes me as having never been better. Comes very plain; position by 6 measures with 405, 76.31 degrees; but the star is two hours from the meridian.

*It was Alvan G. Clark who first observed Sirius B in 1862 while testing a new 18.5-­ inch lens. At this stage, it is fruitful to take stock of the great success Lassell enjoyed with both his 24- and 48-inch specula. Firstly, it is plainly obvious that both instruments were of very high optical quality, even by today’s standards. The reason for this is their long native focal lengths in relation to their aperture. These high f ratio systems are simply very hard to beat in most any situation in which a fair test is presented. Secondly, larger telescopes will always show you more, as Lassell’s observations so clearly demonstrate, provided the ambient conditions are met. Physics is physics. Thirdly, Lassell achieved great things with his reflecting telescopes because of their simple design. He gives

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us no reason to entertain the somewhat false notion that large refractors do any better under similar observing conditions. Indeed, Lassell was firmly convinced of the reflector’s superiority over the refractors of the day. This author is wholeheartedly in agreement with Lassell here, as he has come to know. Fourthly, the reader will note that Lassell did not build an observatory proper for his large telescopes, while observing from Valletta, Malta. He observed in the open air, just like other great observers of the Victorian age, especially the Reverend T. W. Webb and William F. Denning (to name but two). The great American observer E. E Barnard was arguably the first to describe the deleterious effects of so called ‘dome seeing,’ while using the great 40-inch refractor at Yerkes Observatory. Perhaps the relative success of Lassell’s giant telescopes at Malta could in part be attributed to the free circulation of fresh air around the instruments, which insured that they were always close to ambient temperature. That an open tube conferred better images is attested to by a remark made by Piazzi Smyth (the son of Admiral W. H. Smyth) in 1864. In particular, Smyth was told that Lassell’s 48-inch speculum telescope ­produced more stable images free from the usual “twirling and twitching” images resulting from the accumulation of warm air immediately above the telescope mirror. Last but not least, Lassell clearly benefitted from an improved mounting system that allowed these giant telescopes to be used far more productively than those used by earlier/contemporary observers, including the Herschels and the Earls of Rosse. Lassell’s modus operandi is also laid bare in these historic documents. Unlike the Herschels, who were highly systematic in their approach to observing (and rightly so, for the age!), Lassell’s preference was to examine a smaller number of selected objects rather than everything and anything. He was, at heart, a planetary observer. And it paid off for him; he looked at old things in better ways, and they showed him new things! Lassell did offer the use of his 48-inch reflector in the planned southern hemisphere telescope, but, remarkably, his offer was flatly turned down. Disillusioned, Lassell dismantled his great telescope and returned to England in 1865. Remarkably, the world had to wait another quarter of a century before a giant telescope took up permanent residence in the southern hemisphere  – the great 48-inch Melbourne telescope made by Sir Howard Grubb of Dublin, Ireland, at a cost of £5000, which was completed in 1874. We shall briefly return to this telescope in a later chapter. Lassell’s 48-inch would not, in fact, be erected again, but for a time he did use the 24-inch telescope at his retirement home at Ray Lodge in Maidenhead, Berkshire. Here, he sought clearer skies and fresher air than he had enjoyed at Starfield. But his astronomical work waned, as increasingly poor general health and failing eyesight forced him to give observing altogether during the last decade of his life. He did however collate the deep sky observations conducted mostly by Albert Marth, who cataloged a further 600 new nebulae, the details of which were published in the Memoirs of the RAS in 1866. It is somewhat of a mystery to this author why Lassell didn’t leave the telescope in the capable hands of Mr. Marth at Valletta. He was fabulously wealthy (leaving a fortune of over £80,000  in his will, making him a multi-millionaire in modern terms) and could have easily supported Marth to continue the observations. Indeed,

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Fig. 10.10 Simple Nasmyth telescope. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Nasmyth-Telescope. svg)

somewhat disingenuously, he never gave much credit to his diligent assistant, who in fact did most of the observing with the telescopes. As a ‘gentleman’ astronomer, Lassell clearly felt that he deserved the lion’s share of the glory. The great 4-foot mirror ended its life as scrap metal. “I was not without a pang or two, “he wrote, “on hearing the heavy blows of sledge hammers necessary to overcome the firmness of the alloy.” Any discussion on Lassell must necessarily include his long-time friend James Nasmyth, who, like Lassell, abandoned refractors in favor of large reflectors. Hailing from a famous family of gifted artists, Nasymth had a bent towards mechanical contrivances that allowed him to profit from his many patents, including the hydraulic punch, the pile driver and new drilling technologies. As a boy, he enjoyed views of the heavens with his father’s Dollond refractor and benefitted greatly from his acquaintance with Sir David Brewster, who often visited the Nasmyth home at York Place, Edinburgh. Indeed, he had begun casting and figuring speculum telescope mirrors in his teenage years, inventing an improved mold made of an iron plate rather than the traditional sand, which he found improved the strength of the cooling metal. And soon he was producing optically excellent 6- and 8-inch telescopes for his own recreation. At the age of 48, he retired from public life and devoted the rest of his days to constructing and using large reflecting telescopes. After many trials and errors he successfully cast larger mirrors for his friends. Still, like many serious observers of his day, he quickly pined for more aperture. His first success in this regard was the casting of a fine 13-inch blank, which he carefully ground into a first-rate mirror. Looking back fondly on the enthusiasm of his youth he wrote (Fig. 10.10): I know of no mechanical pursuit in connection with science that offers such an opportunity for practicing the technical arts as that of constructing, from first to last, a complete Newtonian or Gregorian reflecting telescope….Buy nothing but the raw material, and work your way to the possession of a telescope by means of your own individual labour and skill. If you do your work with the care, intelligence and patience that is necessary, you will find a glorious reward in the enhanced enjoyment of a night with the heavens.

One of these 13-inch Newtonians was acquired by Warren De La Rue (1815– 1889) in 1842 for his private observatory at Canonbury, a residential district of London, but then later erected at Cranford, Middlesex, with which he created exquisitely beautiful drawings of many celestial objects. After the 13-inch was made, Nasmyth set his sights on a 20-inch telescope, but unlike the Newtonian configuration that he settled on for all his previous instruments, this new telescope would

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Fig. 10.11  The 56-cm Nasmyth-Cassegrain telescope at the Walter-­ Hohmann-­Observatory in Essen, Germany. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Nasmyth_telescope#/ media/File:Walter_ hohmann_sternwarte_ nasmyth_cassegrain_2009. jpg)

involve a clever modification of the Cassegrain design that involved placing a flat mirror at a 45° angle to the optical train of the sub-aperture Cassegrain secondary. This resulted in more light loss but at the expense of gaining a convenient position to view any part of the heavens without having to use a ladder or even having to move from one’s seat. Some light loss was perfectly acceptable to Nasmyth, as he was predominantly a lunar and planetary observer, and he recognized the benefits of comfortable observing, when the eye and brain can process more information. Nasmyth, like many other members of his family, was endowed with great artistic skill, and that much is clear from the many fine drawings he made of Solar System objects. In 1853, he suggested (correctly) that the giant planet Jupiter must have some internal heat source to power the dynamism in the planet’s enormous atmosphere. He was also a keen student of the Sun, conducting many fine observations of sunspots. Indeed, his observations of the fine structure of the solar ­photosphere landed him in controversial waters, when he proposed that, instead of the granulation (a term coined by the Reverend William Rutter Dawes) seen by other observers, the photosphere was actually made up of overlapping willow leaf structures that, according to Sir John Herschel, were “organisms of some peculiar and amazing kind!” Arguably Nasmyth’s finest work was conducted on observing the Moon, where he made arguably some of the most stunning drawings of the more prominent lunar craters. Those drawings still have the power to fill one with awe, even to today. Nasymth’s great personal wealth also allowed him to acquire a few large aperture Cooke refractors in addition to his own reflectors (Figs. 10.11 and 10.12).

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Fig. 10.12  Drawing of a crater on the surface of the Moon by James Nasmyth. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/James_Nasmyth#/media/File:James_Nasmyth_ drawing.jpg)

During the early 1850s, many astronomers had expressed a desire to erect a large telescope in the southern hemisphere, and it is no small wonder that the opinions of Nasmyth, Lassell, Sir John Herschel and Lord Rosse were especially valued. Indeed the Royal Society had set up a committee in 1852, and Nasymth began to draw up detailed architectural plans for such an instrument. The telescope would have a large metal speculum at its heart and would be mounted equatorially.

Sources

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At first Nasmyth considered a conventional solid tube for the instrument, but he also entertained the idea of an open tube in order to minimize thermally induced turbulence around the telescope. This may be one of the earliest known suggestions for a skeleton-tubed telescope. The detailed plans for a large southern hemisphere telescope drawn up by Nasmyth also included some beautiful watercolor illustrations that are preserved to this day by the Royal Society. Some historians of science have suggested that the discussions that took place concerning the construction of a large telescope in the southern hemisphere inspired Lassell to construct his mighty 48-inch equatorial reflector of 40-foot focal length. Nasmyth’s optical genius lives on in the present age, as quite a few observatory-­ class Cassegrains have adopted his innovations to good effect. Yes, the old speculum mirrors are gone, to be replaced by those of glass, coated by either silver or aluminum, which are much easier to work with and give even greater reflectivity. That being said, modern astronomy owes a great deal to these nineteenth century innovators who dared to transform the reflecting telescope into an instrument worthy of carrying on humankind’s quest to understand the origin, composition and fate of that great ocean of space we call the cosmos.

Sources Ashbrook, J.: The Astronomical Scrapbook. Cambridge University Press, Cambridge (1984) Chapman, A.: William Lassell (1799–1880): “Practitioner, patron and ‘grand amateur’ of Victorian astronomy”. Vistas Astron. 32(Part 4), 341–370 (1988a) Chapman, A.: William Lassell (1799–1880): practitioner, patron and “grand amateur” of Victorian astronomy. Vistas Astron. 4, 341–370 (1988b) Chapman, A.: The Victorian Amateur Astronomer. Gracewing, Leominister (2017) Clerke, A.M.: A Popular History of Astronomy During the Nineteenth Century. Dossier Press, 4th edn. (2015) Glass, I.S.: Victorian Telescope Makers: The Lives & Letters of Thomas & Howard Grubb. Institute of Physics Publishing, London (1997) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) King, H.C.: The History of the Telescope. Dover, Mineola (1955) Lassell, W.: Miscellaneous Observations with the Four-foot Equatoreal at Malta. http://articles. adsabs.harvard.edu/full/1867MmRAS.36.33L Lassell, W.: A Catalogue of New Nebulae Discovered at Malta with the Four-foot Equatoreal in 1863 to 1865. http://articles.adsabs.harvard.edu/full/1867MmRAS..36...45L William Lassell (1799–1880) and the Discovery of Triton, 1846. http://www.mikeoates.org/lassell/ lassell_by_a_chapman.html

Chapter 11

Friedrich W. Bessel: The Man Who Dared to Measure

If you can not measure it, you can not improve it. – Lord Kelvin (1824–1907)

Measurement is at the heart of science. It enables us to distinguish between a yard and a mile say, a minute and a year, a gram and a ton. Some measurements don’t count for much, but others can mean the difference between life and death. On another level, measurement enables humans to have a sense of perspective. We are quite enormous in comparison to an ant, for example, but decidedly tiny in comparison to a star. There is a soulful longing within our kind to know, through measurement, where we ‘fit’ in the scheme of things, wistful desires that have given birth to the global civilization we enjoy today. Measurement is closely allied to technological innovation. We have already come across several examples of this in previous chapters  – the businessmen of navigation encouraging progress in timekeeping and positional astronomy, or the abstract theories of Sir Isaac Newton, whose ruminations led to literally thousands of new inventions. But there can be no greater example of this than the exemplary clerk in a house of business, who acquired a taste for numbers through filling up debit and credit columns, and which led him to accomplish something no one had ever done before, to measure the distance to the stars. One of nine children, Wilhelm Bessel (Fig. 11.1) was born in Minden on July 22, 1784, the son of Carl Friedrich Bessel, a government civil servant, and Friederike Ernestine, the daughter of a Lutheran pastor from Rehme. After receiving a good primary school education in Minden, Bessel was enrolled in the local Gymnasium for 4 years but showed very little in the way of talent, finding Latin especially difficult to master. Perceiving that the Gymnasium had failed to inspire the young man, his father secured him a seven-year apprenticeship in Bremen beginning at age 14, working in the import-export business for the company of Andreas Kuhlenkamp. It was in this environment that Bessel’s genius flourished, for apart from his clerical duties, he successfully completed a technical course in navigation, and from there it

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Fig. 11.1 Friedrich W. Bessel (1784–1846). (Image courtesy of Wiki Commons. en.wikipedia. org/wiki/ File%3AFriedrich_ Wilhelm_ Bessel_%281839_ painting%29.jpg)

wasn’t long before his studies led him to astronomy and mathematics, subjects he was to excel in. After completing his apprenticeship in 1804, Bessel contacted Wilhelm Olbers (1758–1840), one of the most distinguished astronomers of his day, concerning a technical paper he had written on the orbit of Halley’s Comet, in which he utilized data from observations made by Thomas Harriot (discussed in a previous chapter) back in 1607. Clearly impressed, Olbers wrote him back, suggesting that he elaborate on some of its details. This he faithfully did, and the paper was duly published to great acclaim. Indeed, Olbers even suggested that on the strength of that paper, Bessel ought to become a professional astronomer, a consideration the young man gave serious thought to and finally committed to. Acting on a recommendation from Olbers, Bessel accepted a post at Lilienthal Observatory in 1806, a private institution near Bremen, owned and administrated by Johann Hieronymus Schröter (1745–1816). There he engaged in a program of observational work on the planets, especially Saturn and its retinue of satellites, comets, as well as the newly discovered asteroids, Ceres, Vesta and Juno, the latter of which was actually discovered at Lilienthal by Karl L. Harding on September 1, 1804. Here also Bessel studied the theory of atmospheric refraction, spherical trigonometry as the well as the elements of celestial mechanics. In 1809 Bessel was offered a string of good positions at a number of German institutions but eventually accepted the post of director of King Frederick William III of Prussia’s new Königsberg Observatory. When he took up the post in May 1810, the observatory was still a work in progress and was not completed until 1813 (Fig. 11.2).

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Fig. 11.2 Königsberg Observatory. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Koenigsberg_ Observatory#/media/ File:ID003729_B162_ Sternwarte.jpg)

His first major work in Königsberg involved the reduction of Bradley’s astrometric data compiled around 1750. This work, appearing in 1818 as Fundamentae Astronomiae pro Anno MDCCLV deducta ex Observationibus viri incomparabilis James Bradley, contained the reduced positions of 3222 stars. Bessel also identified some 71 stellar candidates from this list with unusually large proper motions. With the installation of the new meridian circle by Reichenbach in the autumn of 1821, Bessel, together with his assistant, F. W. Argelander (Fig. 11.3) (1799–1875), initiated an ambitious project to determine the accurate positions of all stars down to the 9th magnitude in the swathe of sky between +15° and −15° declination. In 1825, they extended this range to +45°, culminating in 1835 with a new catalog of 75,011 stars, organized into 536 zones. Indeed, Argelander continued this work to create his now famous Bonner Durchmusterung, first published in 1852. As one of Europe’s choicest mathematicians (having never attended university!), Bessel developed an unusually deep interest in the factors that affect measurements.

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Fig. 11.3 F. W. Argelander (1799–1875). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Friedrich_Wilhelm_ Argelander#/media/ File:Friedrich_Wilhelm_ August_Argelander_1852. jpg)

His results are summarized in the Tabulae Regiomontanae Reductionum Observationum, published in 1830. Bessel also discovered the so called “Personal Equation,” the effect of the observer’s personality and circumstances on the science of astrometry. And he was one of the first to identify the systematic errors that derive from using scientific instruments. Indeed, he wrote no less than 23 peer-reviewed articles on this prosaic topic, but, as we shall see, it was this almost obsessive attention to detail that would immortalize his name in the annals of astronomical history. Bessel and Argelander’s new star catalog allowed them to establish the proper motions of the bright winter luminaries, Sirius and Procyon. Indeed, Bessel deduced that both these stars must have an unseen companion that made them wobble ever so slightly as they moved through space. And though he never lived to see his deductions vindicated, they were both confirmed to have white dwarf binaries in 1862 and 1892, respectively. For two centuries, many astronomers had believed that if they could measure the annual parallax of a star, that is, using the diameter of Earth’s orbit as a baseline, they might just be able to measure their distances. And since it was reasonable to assume that stars with the greatest proper motion ought to be closer to us, Bessel began to select targets that might be used to perform such a measurement. Some astronomers, such as James Bradley and Giuseppe Piazzi, thought they had mea-

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sured such changes: 2- and 1.5 -seconds of arc , respectively, for the most favorable instance, the 6th magnitude orange dwarf star, 61 Cygni. He knew these were ­incorrect, though, as what his fellow astronomers had measured as parallax was in fact attributed to errors of observation. Bessel devised a much superior method that would reduce this observational error by about an order of magnitude, but to do so, he relied on the precision offered by the best optician in the world. Enter his compatriot, Joseph von Fraunhofer (1787–1826). Born in Bavaria in 1787, Fraunhofer’s father eked out a meager existence as a glass maker and consequently could ill afford to have his youngest son receive more than a few years of elementary schooling. Thus, like so many other children of that time who were born to less well-off parents, Fraunhofer had little choice but to begin working in the family workshop at the tender age of ten. Upon his father’s passing in 1789, Fraunhofer became an apprentice to a lens maker based in Munich. Although still very young, the lad showed much promise, but his employer, a one Mr. Weichselberger, continued to exploit his talents primarily as slave labor, driving the boy to near-starvation and exhaustion. However, in a curious twist of fate, the most fortunate day of Fraunhofer’s life was arguably his most perilous, for on the night of July 21, 1801, the shoddily constructed building in which he slept collapsed, trapping him beneath the rubble. After the local community had been mobilized, a full-scale rescue operation ensued, and the boy was rescued, largely unscathed. As luck would have it, the Elector of Bavaria, Maximilian IV Joseph, was also present to witness the scene, and was so moved with compassion for the desperate predicament Fraunhofer was now in, that he awarded him enough cash to enable him to buy his way out of the ‘sweatshop’ apprenticeship which he was coerced into in the aftermath of the death of his parents (Fig. 11.4). Fig. 11.4  Joseph von Fraunhofer (1787–1826). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Joseph_v_Fraunhofer. jpg)

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Although he foolishly squandered much of his pecuniary award on a get-rich-­ quick scheme, Fraunhofer did manage to retain sufficient funds to remain in Munich for several years. In 1806 he had secured employment with the prestigious Philosophical Instrument Company of Munich, which supplied scientific optical equipment of the highest quality to its customers around the world. It was here that the young man was first able to demonstrate his well-developed skills in working glass, and fashioning lenses and prisms that were devoid of the usual striae, air bubbles, colorations and other artifacts. It was here also that Fraunhofer became acquainted with Pierre Louis Guinand, a Swiss glass technician. But they were soon headhunted by Georg von Reichenbach and Joseph Utzschneider, who had founded a new firm devoted to optical glass making based in Benediktbeuern, Bavaria, a secularized Benedictine monastery. In 1814, Guinand left the firm, as did von Reichenbach, whereupon Fraunhofer became a partner. By any measure of success, these were the golden years of Fraunhofer’s life, where he learned to construct large glass blanks of very high quality, built his first spectroscope, diffraction grating, as well as grinding the finest lenses the world had ever seen. Unlike all those other workers of glass who came before him, Fraunhofer approached the fashioning of an achromatic doublet lens in a systematic way, accurately measuring the refractive indices and dispersion properties of his glass combinations, as well as being the first to understand how the precise curvature of the lenses he employed would correct for coma and astigmatism. This was in sharp contradiction to all of his predecessors, who were accustomed to matching one piece of crown glass with another of flint by trial and improvement. In essence, Fraunhofer was the first optician to approach the creation of objective lenses in an essentially modern, scientific way. At Benediktbeuern, Fraunhofer zealously set himself to the task of creating the largest object glass yet made. After many false starts and annoying technical setbacks, he managed to create a new object glass fully 9.5 inches in diameter, with a focal length of 14  feet that was completed on December 12, 1817. This was the objective lens that was fitted to the great Dorpat refractor, dedicated in 1824, which was so productively used by the F. G. W. Struve in the elucidation of some 2000 new double stars (Fig. 11.5). The success of the classical achromatic refractor in the decades ahead has been exhaustively documented by this author, especially in the mensuration of double stars, for which they were tailor made. Little did Fraunhofer know that these telescopes served up the most stable images of all telescope designs (modern ED refractors included) owing to a number of unique attributes previously explored, including very closely matched coefficients of thermal expansion (an accident!) of the crown and flint objective elements, as well as their high native focal ratios necessitating gently curved lens geometries. One need only look at the resolution feats of the great Lick refractor in America, for example, or the great Meudon refractor (both of which are discussed elsewhere in this book) in France, to see just how well they did in this regard.

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Fig. 11.5  The great Dorpat refractor built by Joseph von Fraunhofer in 1817. (Image courtesy of Commons. https://en.wikipedia.org/wiki/File:Teadusfoto_2015_-_04.jpg)

The success of Fraunhofer was soon brought to the attention of Bessel, who ordered up a very special object glass of his own, one that would enable him to carry out the precise measurements he needed to make on 61 Cygni in order to establish its parallax. Enter the divided object glass heliometer. First suggested by the Danish astronomer O. Römer in 1675, the earliest example of a divided object glass was realized by George Dollond in 1753. As its name implies, it consists of an object glass divided into two semi circles. Because it was originally designed to measure the diameter of the Sun, it came to be known as a heliometer. When the two halves of the object glass are coincident with each other, the objective yields a single image of a pair of stars. When a very fine screw is used to push one element relative to the other (held stationary) along the central axis, a double image is seen. The angular displacement is measured by matching up the opposing star images with each other. Though obsolete nowadays, the heliometer

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S1

S2

T1

T2

Fig. 11.6  The principle of the divided object glass. (Image courtesy of The Free Dictionary. https://encyclopedia2.thefreedictionary.com/heliometer)

was good enough to measure angular displacements as small as a few tenths of an arc second (Fig. 11.6). Fraunhofer, unfortunately, would not live long enough to see the heliometer, with its exquisite 6.5-inch divided object glass, delivered to Bessel in 1829. The desperate conditions in which he grew up certainly must have taken their toll, and his official death certificate stated that he had succumbed to tuberculosis. Bessel started to work with the instrument, learning how best to calibrate it and performed a series of trial micrometer measurements of various celestial bodies, including the planets and some well-known binary star candidates. Indeed, by 1833 Bessel published a catalog of 38 double stars, finely measured with the Fraunhofer heliometer. Beginning in 1837, Bessel began the painstaking work of measuring the precise position of 61 Cygni with respect to a faint background star (which had no measurable parallax). This exacting work, often done under freezing winter conditions, continued for a whole year, after which he was able to compute a parallax of 0.3136″. He then had the heliometer taken down to be serviced and resumed the measurements, ending in March 1840 with a series of 402 measures, resulting in a revised value of 0.3483″. Simple trigonometry provided the linear result; 61 Cygni was about 600,000 times further away than Earth is from the Sun! In other units, Bessel’s measurement came to 10.3 light years, just over one light year less than the modern accepted value of 11.4 light years (Fig. 11.7). The accurate determination of the first stellar parallax, as enunciated by Bessel, marked one of the major milestones in the prodigious conquest of the heavens by human intelligence. Until this time, that conquest had been limited to the shallows of the Solar System, with all reconnaissance operations mounted beyond it having flatly failed. This distance, nearby in comparison to other stars, demonstrated the terrifying immensity of the stellar Universe. Our world is a precious little oasis in a cosmos vast beyond ordinary human understanding. Unbeknown to Bessel, however, there were other astronomers hard at work establishing similar measurements – most notably at the Cape of Good Hope, South Africa. In 1831, the Cape Observatory had just been established under the directorship of a Scotsman, Thomas Henderson (1798–1844). Originally trained in jurispru-

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Fig. 11.7  Heliometer at the Kuffner Observatory (Vienna, Austria). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/File:Heliometer_Kuffner-Sternwarte.jpg)

dence, Henderson’s talents for numerical astronomy were recognized by the physicist, Thomas Young (1773–1829), who wrote a letter recommending Henderson take his place as superintendent to the Admirality of the Royal Navy in the event of his death (Fig. 11.8). Shortly after accepting the position, Henderson was stationed by warrant at the Royal Observatory, South Africa, and assigned to making similar measurements to Bessel on the bright antipodean star, Alpha Centuari, between 1832 and 1833. Describing his stay in South Africa as “the most miserable of his career,” his first estimate was that Alpha Centauri had a parallax of about 1 second of arc, that is, about 3.5 light years away. Further measurements produced a downwards revised value of 0.75 seconds of arc, or about 4.5 light years. Had he published these results at this time, Henderson would have pipped Bessel at  the post as the first person to accurately measure a stellar parallax. However, owing to suspicions concerning the quality of the instruments he employed and being acutely aware that false parallaxes had been announced before, Henderson delayed their publication at first, waiting for further observations by his successor, Thomas Maclear. A lesser man might have become embittered in accepting second place in the great space race of the mid-nineteenth century, but the historical consensus suggests that Henderson openly accepted Bessel’s right to win the honor, as he had published earlier. Indeed, there is good evidence that both astronomers remained firm friends for the rest of their lives. Sadly, those lives were cut very short in the scheme of things. Henderson died suddenly a few weeks before his 46th birthday. A post-mortem revealed “hypertrophy of the heart.” Bessel suffered a severe loss when his son, Wilhelm, died in 1840 aged just 27. In the years that followed, he and his daughter, Elisabeth, traveled to a

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Fig. 11.8  Thomas Henderson (1798–1844). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Thomas_Henderson_%28astronomer%29#/media/File:Thomas_James_ Henderson,_1798–1844_Henderson-01r.jpg)

few scientific venues in France and England, where he was universally lauded for his work. He died in Königsberg on March 17, 1846, from a somewhat mysterious disease that some physicians have attributed to intestinal cancer. He was a mere 62 years on Earth. Among the many accolades Bessel received from his astronomical peers are these two: • Sir John Herschel, speaking on behalf of the Royal Astronomical Society, called his work, “the greatest and most glorious triumph which practical astronomy has ever witnessed,” for which he was awarded the Gold Medal (for the second time) in 1841. • Dr. Olbers, on the occasion of his 80th birthday, declared that Bessel “put our ideas about the Universe for the first time on a sound basis.” In an age where the classical achromat has been ignobly treated by a generation that cares little or nothing for its illustrious heritage, this author feels especially privileged to honor these great men of science and the instruments they used to such great effect. Long live the classical refractor!

Sources

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Sources A Biography of F.W. Bessel. http://messier.seds.org/xtra/Bios/bessel.html Clerke, A.M.: A Popular History of Astronomy in the Nineteenth Century. Dossier Press, New York (2015) English, N.: Classic Telescopes, A Guide to Collecting, Restoring and Using Telescopes of Yesteryear. Springer, New York (2014) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Jackson, M.: Spectrum of Belief, Joseph Von Fraunhofer and the Craft of Precision Optics (Transformations: Studies in the History of Science and Technology). MIT Press, Cambridge, MA (2000) King, H.C.: A History of the Telescope. Dover, Mineola (1995) More on the Heliometer. http://encyclopedia2.thefreedictionary.com/heliometrical More on Thomas Henderson. http://piazzi.uk/caltonhill/astronomerroyals/henderson/henderson. html

Chapter 12

W. H. Smyth: The Admirable Admiral

The early Victorian period represented an exceptionally changeable time for astronomy. On the continent, the French, Russians and Germans had established large observatories with professionals at the helm. The United States, still a sleeping giant, had not yet realized her latent talent for producing some of the finest refracting telescopes in the world. But as John Weale reported in an account of London’s observatories in 1851, privately owned establishments, run by wealthy amateurs, were all the rage across England and indeed had become ‘fashionable.’ Immersed in this ‘gentleman astronomer’ culture, William Henry Smyth (1788–1865), a retired sea captain and later admiral in the Royal Navy, flourished (Fig. 12.1). Born in London in 1788, Smyth’s childhood was, by all accounts, a happy one, with long days filled with adventure. But for us amateur astronomers, it is his last 40 years that we cherish most. The son of an American loyalist who had returned to Britain after the Revolution, Smyth fancied himself as a bit of a Captain Cook. After climbing on board a merchant ship that had docked in the Thames, he had run away to sea as a lad. And there he stayed, joining the Royal Navy during the height of the Napoleonic Wars, when Lord Nelson had rose to become the hero of ‘Free Europe’. Much of his early naval career was spent in the Mediterranean serving under Lord Rodney, and assigned to the pro-British naval base at the Kingdom of Naples and Sicily. By his early twenties, he had been promoted to his first command of a small squadron in the Straits of Messina, where he helped keep the anarchy of the Barbary Pirates at bay. For his gallantry, Smyth was likely the recipient of many cash prizes which made him quite wealthy by the standards of his subordinates. And it was during these years serving with the British Squadron that Smyth was invited to the Court of King Ferdinand IV of Naples, where he made the acquaintance of the illustrious Italian astronomer, Father Giuseppe Piazzi, who had already earned a piece of immortality by discovering the first asteroid, Ceres, back in 1801. Despite his fervent Protestantism, Smyth found a kindred spirit in the Italian Catholic who was to make a lasting impression on the upwardly mobile Englishman, by opening the young man’s eyes to the possibilities a scientific career might bring. Smyth soon sought out the great observatories of Europe, learning how to use the © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_12

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Fig. 12.1  Admiral William Henry Smyth (1788–1865). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:W_H_Smyth.jpg)

astronomical instruments at the Royal Observatory, Greenwich, as well as those established at Palermo, Sicily. Curiously, in the same way that Lord Nelson had met his future wife, the Lady Hamilton, while at the Neapolitan Court, so too did Captain Smyth become acquainted with Miss Annarella Warrington, the only daughter of a future British Consul, T. Warington, Esq., at the same court. They subsequently married in 1815, and unlike Nelson’s, the matrimonial union proved a long and happy one. Indeed, she was his companion and assistant in all his scientific work. Some of their children were born in Sicily and as father to three daughters  – Henrietta, Ellen and Rosetta – Admiral Smyth cultivated their pashion for civilised learning, instructing them in practical astronomy, navigation and mathematics. Their son, Charles Piazzi Smyth, ventured to the Cape Observatory, South Africa in 1835 at the tender age of 16 where he was schooled in all aspects of astronomical science under the direction of his father’s friend, Thomas Maclear. After 11 years of training, Piazzi was later to become one of the most notable figures in the Victorian scientific movement becoming the Astronomer Royal for Scotland in 1846, as well as professor of astronomy at Edinburgh University. After the fall of Napolean and the liberation of Europe, Smyth served out his time in the eastern Mediterranean, undertaking hydrographic surveys. Supporting a young family, he remained in Naples until 1825 but thereafter ‘retired’ to England, living out the life of a country Laird in Bedford, where he soon assumed the mantle

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of the Gentleman Astronomer, a persona that subsequent generations would hold in great affection. From his opulent country home, Smyth constructed an elegant observatory, equipping it with a transit instrument and an accurate timepiece with which he could measure both the right ascension and declination of stars as they trundled across the meridian. He also had in his possession a small refracting telescope astride a solid mounting, which he could move around his estate. Charging it with high-quality micrometer eyepieces, he undertook measurements that would better quantify the refractive index of the air, by accurately recording stellar positions. By about 1830, Smyth acquired a 5.9″ equatorial refractor by Charles Tulley of 8.5 foot focus from Sir James South, who purchased the instrument for the capital sum of £220 during a trip to Paris. Probably very good by modern standards, it represented one of the largest and most sophisticated refractors in Britain. With this telescope, Smyth began a long program of original research on double and variable stars, and showing an unusual interest in star colors (Fig. 12.2).

Fig. 12.2  A schematic of Admiral Symth’s 5.9 inch Tulley refractor, with Dr. John Lee (seated). (Image courtesy of the Royal Observatory, Greenwich)

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Smyth’s new-found passion for advancing the cause of visual astronomy blossomed in the fertile soils of the British empire, where his contemporaries – men of the ilk of Sir John Herschel, William Rutter Dawes and Sir James South  – were carrying out exciting new researches from the comfort of their grand estates. It was during these seminal years that Smyth first made his acquaintance with the wealthy barrister and squire of the great Hartwell estate, Aylesbury, a one Dr. John Lee. Passing through Bedford while traveling to the County Quarter Sessions Courts, Lee often stopped off at Smyth’s house, where he enjoyed the use of the admiral’s fine instruments. Indeed, under Smyth’s aegis, Lee constructed his very own observatory (Hartwell), equipping it with the finest astronomical contraptions money could buy. And though they remained firm friends, kindred astronomers as it were, their personalities couldn’t have been more different. Dr. Lee, the embodiment of Victorian idealism, was a staunch teetotaler, eschewing the activities of gambling and the pleasures of hunting – the time-honored pastimes of many of his peers. Smyth, on the other hand, had acquired many of the habits of his seafaring comrades, indulging in the culinary delights of good food and the various libations his social station had lent itself to, as well as expressing a decidedly more conservative political worldview. Yet, each man thrived in each other’s company, hosting numerous astronomical gatherings. Indeed, while Dr. Lee was constructing his lavish observatory, he would issue a certificate of merit to anyone who would lay a commemorative brick towards its completion. But his brick layers were no ordinary plebs; indeed they were the nobilitas of the Imperium Britannicum, and future presidents of the prestigious Royal Society, including names like Airy, Brewster, Struve, Herschel and Rumker. Wealthy ‘commoners’ were also welcomed with open arms, though, including the tycoon landowner-­ brewer Samuel Whitbread, who had himself built private observatories at his palatial London home at Eaton Square. Both Dr. Lee and Captain Smyth, as active Fellows of the Royal Astronomical Society (FRAS), began to publish numerous papers on various astronomical topics. But it is arguably Smyth’s 1844 work, A Cycle of Celestial Objects, that caused him to become more generally known. Distilling some 20 years of experience in matters of practical astronomy and astrometry into 543 pages, this work covered the stellar real estate of 70 constellations, which greatly aided Smyth’s rise to fame among the international astronomical community. It is immediately apparent that its author had spent thousands of hours studying the heavens. In this beefy, two-volume work, Smyth published many useful tables (which the American poet Walt Whitman would later write about with derision) of the celestial real estate he had visited, together with invaluable advice on their location and study. It is here that one will also find a treatise on Gamma Virginis (Porrima), one of  the first double stars, the orbital aspects of which had just been established through careful study. Though the vast majority of the work in the Cycle was Smyth’s own, there are occasional references other observers, particularly Benedict Sestini in Rome, Italy. Yet, seen through the lens of modernity, Cycle in the Heavens could certainly not be considered to be an easy work to digest. Indeed, Smyth presupposes that his

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readers possess quite a sophisticated background in trigonometry, optics and linguistics, particularly Latin and ancient Greek as well as a few modern European languages. But as terse as it sometimes seems, Smyth’s magnum opus need not be construed as being deliberately elitist. It is more accurately described as a reflection of the status of astronomy in the society of the day, when almost all amateur astronomers were well educated, well to do and in possession of considerable amounts of leisure time. Smyth was a man of his time, classically trained for the Age of Empire. If anything, it just illustrates the sheer gulf between the haves and have-nots of the day, as well as the circles within which the good admiral and his chums moved. For Smyth, the squalor of a London slum was a distant and unthinkable possibility. In the Cycle, Smyth also described in great detail the constitution of his own observatory at Bedford. The ‘truncated dome’ ran on wooden balls, where, on a favorable evening, his beautiful, 5.9-inch Tulley refractor peered out. In addition to the main circular space, Smyth also had constructed ancillary ‘transit’ and ‘computing’ rooms, where his rough numbers, derived from the micrometer, could be reduced. Yet, as successful as the Cycle was, it did not meet with universal praise. For example, in 1879, the English astronomer Herbert Sadler published a paper in the RAS Monthly Notices, where he claimed that Smyth had lifted quite a few double star entries straight out of the notebooks of Sir John Herschel, but later studies seemed to vindicate his work as entirely genuine. More trouble beset the Cycle in 1879 through 1880, when the great American double star observer, S. W. Burnham (discussed at length in a later chapter) set out to re-measure Admiral Smyth’s catalog of double stars using the 18.5 inch refractor at the Dearborn Observatory in Chicago. Burnham suggested that for some classes of double star, Smyth only provided estimates of their position angles and probably didn’t measure them. Though the general descriptions of the stellar systems Smyth visited with his telescope are delightful in the extreme, some remain rather puzzling. For example, one is immediately drawn to the extraordinary range of star colors Smyth employed. Many contemporary observers are left none the wiser about the complexion of the components of the binary system, 95 Herculis, for example, which to some present with a golden tint. Yet, the jolly admiral described the same stars as ‘apple green’ and ‘cherry red.’ Perhaps it was the alcohol talking, or maybe it was attributed to the imperfect achromaticity of his 5.9-inch. We shall never know for sure. Certainly, anyone with extensive experience with achromatic refractors affirms the potential to exaggerate the colors of stars at high magnification. The refractor, however well corrected it is, can never reveal the true color of any star. And that holds true even for modern apochromatic refractors, which approximate reality but never quite get you there. In contrast, modern reflecting telescopes, which reflect all wavelengths of light equally, do provide the observer with true star colors, and at a fraction of the cost of the best refracting telescopes. In retrospect, we only know so much about the activities of the Victorian Grand Amateur culture because Dr. Lee’s Albums and Scrapbooks of the Hartwell estate have been so well preserved at the Museum for the History of Science at Oxford, UK. Another issue that needs to be clarified is the role of women in such a society, with the common misconception that members of the fairer sex were really second

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class citizens in Victorian society holding sway. Yet, the Albums clearly record the attendance of ladies and children, who appear to have been warmly welcomed into these grandiose Victorian ‘mancaves,’ drinking up the views through the magnificent refractors erected therein, or perhaps weighing up the latest theories of cosmogeny with their spouses and other male acquaintances. William Henry Smyth had his place in the pecking order, too. He was not as wealthy as Dr. Lee. Indeed, Smyth once described himself as a ‘half pay naval officer,’ implying that he lacked the true, landed wealth of his magisterial friend at Hartwell. By 1853, he had acquired the rank of rear-, followed shortly afterwards by vice-admiral. Only in 1863 was Smyth promoted to full admiral, though by that time, he was nothing more than a beached officer. Indeed, the publication of Smyth’s Cycle in 1844 may have reflected an underlying financial crisis in his life. Diligent research carried out by the British historian of science, Dr. Allan Chapman, has shown that the early 1840s were characterized by a volatile financial market, both at home and overseas, with many banks and mercantile companies crashing out. Indeed, this may well have been the motivation behind the sale of Smyth’s 5.9-inch refractor to Dr. Lee and its re-housing at Hartwell House. Despite its new ownership, it is certain that Admiral Smyth spent a great deal of time at the observatory housing the 5.9-inch Tulley refractor at Hartwell, but he did all of his observations in a completely unpaid capacity. But by 1858, now aged 70 years, Smyth had said farewell to his erstwhile pastime, providing a recommendation to Dr. Lee that Norman Pogson, then at the Radcliffe Observatory in Oxford, was suitably qualified to carry on the work on double star mensuration. In the autumn of his life, Admiral Smyth’s conviviality was known the length and breadth of the country. We now know of many correspondences he made with gentlemen in Liverpool and Nottingham in the 1850s. Indeed, by the 1860s, there would have been few places in the British Isles that did not have an astronomical society of sorts, equipped with ever more impressive instruments donated by the wealthy patrons. When Smyth started his astronomical adventures, a 5.9-inch object glass was considered world class. Thirty years on, refractors as large as 10 inches were being used by gentlemen amateurs, continuing in the good admiral’s footsteps. His lifelong friend, Dr. Lee, survived him by only a year, as Smyth passed away in 1865, and with their passing, much of the instrumentation became entrusted to the RAS.  The famous 5.9-inch equatorial is now in safekeeping at the Science Museum in South Kensington, London (Fig. 12.3). Admiral Smyth’s Cycle was reprinted in 1986, and in the Foreword to that edition the astronomer and writer George Lovi writes, “What makes it so special is that it is the first true celestial Baedeker and not just another “cold“ catalog of mere numbers and data. Like the original Baedeker travel guidebooks of the last century, this work is full of colorful commentary on the highlights of the heavenly scene and heavily influenced several subsequent works of its type, even to the present day: “It is in the descriptive material that Smyth is a delight. He not only describes what the user of a small telescope will see, but also includes much fascinating astronomical,

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Fig. 12.3  The Great Comet of 1811, as drawn by William Henry Smyth. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ William_Henry_Smyth#/ media/File:Comet_ of_1811.jpg)

mythological, and historical lore. Many of these descriptions are especially valuable for the novice and user of small telescopes of a size similar to Smyth’s.” The enterprising spirit of Admiral Smyth lives on in the twenty-first century, when his descendants, equipped with telescopes not too dissimilar to the refractor that made him famous, continue to ply the heavenly seas in search of booty. And even if you accomplish 10% (5%?) of what the jolly admiral had achieved in his career, then that would be an astronomical life worth celebrating!

Sources Chapman, A.: The Victorian Amateur Astronomer, Independent Astronomical Research in Britain, 1820–1920. Gracewing, Leominister (2017) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Peeling. R.: Rediscovering the Bedford Catalogue for the 21st Century. http://www.webbdeepsky. com/articles/rediscovering-the-bedford-catalogue Smyth. W.  H: Cycle of Celestial Objects. https://ia601401.us.archive.org/21/items/cycleofcelestial031506mbp/cycleofcelestial031506mbp.pdf

Chapter 13

The Stellar Contributions of Wilhelm von Struve

In the last years of the eighteenth century, the socio-political map of Europe was rapidly changing. In France, Napoleon Bonaparte had risen to power, and his armies had overrun Germany, plunging it into political and economic upset, a time where the world’s great empires  – British, French, Dutch and Russian  – jockeyed for power. Yet, amidst this turmoil, a new center of learning was established at Dorpat Observatory in Russia, the brainchild of the great astronomer Wilhelm von Struve (1793–1864), which soon became the envy of the astronomical world. Like many great astronomers from the golden age, the career of Wilhem von Struve (Fig. 13.1) was more accidental than preordained. He was born in Altona, Duchy of Holstein (then a part of the Denmark-Norway kingdoms), near Hamburg, the youngest of 18 siblings of Jacob Struve (1755–1841), a trained mathematician and principal of the local school attended by his son. There, the boy quickly gained a reputation both as an accomplished athlete and a student of great academic promise. In 1808, so the story goes, Struve was taking a stroll along a street in the Hamburg suburb of St. Pauli when he fell into the hands of a French press gang seeking to enroll army recruits. He soon escaped, though, and Struve’s father moved the family away from the French occupation to Dorpat (modern Estonia) in imperial Russia, to avoid military service, equipped with Danish passports. The same year, the 15-year-old entered the Imperial University of Dorpat, where he first studied philology but soon tired of it, turning his attention instead to mathematics and astronomy. During his student years, he supported himself by offering his tutelage to wealthy patrons. Struve received his doctorate at age 20, having done a thesis on the latitude and longitude of Dorpat Observatory. Between 1813 to 1820 Struve secured a permanent post there and taught at the university. With his position secured at Dorpat, Struve returned to Altona to visit his parents and became engaged to his sweetheart, Emilie Wall (1796–1834), whom he married in 1815. Their matrimony was long and happy, and she bore him 12 children, eight of which survived childhood. His handsome appearance and cordial personality won him many nota-

© Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_13

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Fig. 13.1  Wilhelm von Struve (1793–1864). (Image courtesy of Wiki Commons. https://upload. wikimedia.org/wikipedia/ commons/5/5a/Struve.jpg)

ble friends. During his period away from Dorpat, Struve visited the established German observatories, forging friendships with the prominent astronomers of the age, including Friedrich Wilhelm Bessel, Heinrich Olbers, Johann Schröter and the great mathematician, Carl Friedrich Gauss. The observatory at Dorpat was erected in 1810 and was originally topped with a dome that was replaced in 1822 by a more elaborate, cylindrical structure equipped with a large transit instrument by the famous English telescope maker Dollond, a Baumann repeating circle for the determination of star altitudes as well as a Herschelian reflector of 7-foot focus. Its director, Professor Johann Huth, suffered chronic ill health, and by 1820 Struve became a full professor and director of the observatory. Developing a keen interest in double stars, Struve became pre-­occupied with their research, using both the transit instrument and a smaller 3.5-inch aperture Troughton refractor (purchased in 1807) of 5-foot focus in their pursuit. As his interest in double star astronomy and geodesy deepened, Struve began to seek out a larger instrument that would establish Dorpat as a major center of world-­ class astronomical research. In 1820, Struve paid the great German optician, Joseph von Fraunhofer, a visit in Munich to find out how large a telescope he could make. Thanks to a generous grant from the university – which had the Romanov imperial family as its patron – Struve was able to place an order for the largest and most modern refracting telescope to grace the world. Its aperture was to be 9 Paris inches (9.6 modern inches), and mounted on a sturdy, clock-driven equatorial mount. In 1824, von Fraunhofer had completed the instrument and painstakingly shipped it in 22 crates from Munich. Eager to ensure a safe transit, Struve dispatched one of his students to serve as an escort. Finally, on the fateful day of November 10, 1824, a grand procession of horse-drawn carts arrived at the observatory, where the main instrument and many fine optical and micrometrical accessories, was carefully

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unpacked. Curiously, Fraunhofer had failed to include instructions on its assembly but that didn’t deter Struve, who, using only a drawing he received from Fraunhofer earlier, managed to put the grand instrument together in just 5 days! The Dorpat 9.6 inch achromatic refractor had a focal ratio of 18 and was mounted on a beautiful wooden pier. Its tube was fashioned from fir wood and covered with a mahogany veneer that gleamed like polished copper, while its declination and hour circles had a silvery gleam. A couple of long, slender rods were mounted on either side of the instrument to minimize tube flexure. This was not only the most powerful telescope on Earth at the time but was also the most beautiful. The telescope was temporarily located in the western hall of the observatory, where a high, south-facing window provided an unobstructed view of the heavens. Fraunhofer’s telescope was restored in 1993 under the guidance of Enno Ruusalepp and now enjoys a new lease of life in the museum of Tartu Old Observatory, Estonia. As magnificent as the telescope looked astride its state-of-the-art equatorial mount, its optical evaluation was still forthcoming. That opportunity arrived on November 16, during a clear spell in the wee small hours. Examining the Moon and a suite of double stars, Struve proclaimed, “This magnificent work of art was doubly astonishing both for the excellence of its design and construction, and for its great optical power and the quality of its images.” In the words of Dr. Joseph Ashbrook, former editor of Sky & Telescope, “Wilhelm Struve’s first use of the Dorpat refractor marked a major milestone in astronomical history. The great, clumsy, altazimuth reflectors of the Herschels’ became obsolete on that date, for Struve had begun to measure double stars with the first modern telescope.” With the Great Dorpat refractor, Struve discovered 3134 double stars in a 3-year-­ long study, publishing his work in his magnum opus, Catalogus Novus Stellarum Duplicium (1827), which was refined over the decades until his retirement. Indeed the records at Dorpat reveal that 120,000 stellar pairs fell between the spider lines of his micrometer! The great telescope was also employed to measure the angular sizes of the major planets and their satellites, and Struve also carried out important observations of comets. The mechanical excellence of the telescope enabled Struve to work with extraordinary efficiency. Approximately 400 objects could be viewed at very high powers (typically 700 diameters), one object every 9 seconds! In just three years, he had examined an astonishing 20,000 objects, discovering a new double star for every 38 single ones examined! By anyone’s standard this was an extraordinary rate of discovery! Struve remained at Dorpat until 1839, after which he founded and became director of the new Pulkovo Observatory near St. Petersburg. The new Czar, Nicholas I, was determined to outdo the achievements of his predecessor, Peter the Great, and this included making the nation a world leader in astronomical science. He and his advisers chose a very suitable site for a new observatory at Pulkovo Hill, some 10  miles southwest of the city of Neva. The main observatory was annexed to a complex of other buildings bristling with turrets. Here, amid 54 acres of land, Struve was commissioned to put the most sophisticated telescope the world had yet seen, sparing no expense. Sure enough, Struve went straight to Munich, to the workshops

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of Merz & Mahler, where he ordered up an even larger refractor of 15-inch clear aperture, together with a large heliometer (an instrument discussed at length in Chap. 11), as well as a wide assortment of secondary instruments. The recipient of many honors, the elder Struve won the Gold Medal of the Royal Astronomical Society in 1826. He was elected a Fellow of the Royal Society in March 1827 and was awarded their Royal Medal the same year. Struve was also elected as a member of the Royal Swedish Academy of Sciences in 1833. In 1843 Wilhelm formally became a Russian. Struve carefully measured the “constant of aberration” in 1843. He was also the first to measure the parallax of Vega, although, as we have seen, Friedrich Bessel and Thomas Henderson had been the first to measure the parallax of a star (61 Cygni and Alpha Centauri, respectively). He was also one of the pioneering astronomers to identify the effects of interstellar extinction (though he provided no mechanism to explain the effect). His estimate of the average rate of visual extinction – 1 magnitude per kpc – is remarkably close to modern estimates (0.7 to 1.0 magnitude per kpc). Struve was also interested in geodetic surveying, and in 1831 published Beschreibung der Breitengradmessung in den Ostseeprovinzen Russlands. He initiated the Struve Geodetic Arc, which was a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through ten countries covering a 2820 km distance, in order to establish the precise dimensions of Earth. He retired in 1862 due to failing health and died 2 years later on the morning of November 23, 1864. Pulkovo Observatory would become the birthplace of the Struve dynasty. Struve’s son Otto (1819–1905) was from his second marriage to Johanna Bartels, who was daughter of the mathematician, Martin Bartels. Otto continued his father’s work, discovering a further 500 pairs with the 15-inch refractor and directing the institution from 1858 until 1899. The collective work of the Struves established the orbits of some 20% of all the binary star systems known to date. His name, as well as that of his sons, Otto and Karl, are immortalized by the naming of asteroid 768 Struve, and a lunar crater was named for another three astronomers of the Struve family: Friedrich Georg Wilhelm, Otto Wilhelm and Otto. The Struve astronomical dynasty continued well into the twentieth century, when Wilhelm’s great grandson, Otto (born 1897), broke with tradition by emigrating to the United States, becoming director of Yerkes Observatory and founding both the McDonald and Leuschner observatories. Otto Struve also acted as president of International Astronomical Union between 1952 and 1955 (Fig. 13.2). It is difficult to summarize the achievements of this great astronomer from the golden age. Perhaps it is fitting to quote the words of the Reverend C. Pritchard, who wrote a short biography of the man in the Astronomical Register (1865): Whatever is mortal of Wilhelm Struve, rests in the churchyard attached to the beloved institution which he so long adorned. His grave lies under the shadow of its domes and was selected by himself: yet it is not these domes alone which constitute its monument; the spirit of the man still breathes in the zeal, the labours, the unanimity, which survive the master, and reign within them. That spirit will be reproduced again and again in future ages, when other men, animated by the story of his example, shall endeavor to follow in his steps.

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Fig. 13.2  University of Tartu Old Observatory, housing the great Dorpat refractor. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/University_of_Tartu_Old_Observatory#/ media/File:Old_Observatory,_Tartu,_April_2012.JPG)

Sources Ashbrook, J.: The Astronomical Scrapbook. Cambridge University Press, Cambridge (1984) Aubin, D., et al. (eds.): The Heavens on Earth. Duke University Press, Durham (2010) Clerke, A.M.: A Popular History of Astronomy in the Nineteenth Century. Dossier Press, New York (2015) Couteau, P.: Observing Visual Double Stars. MIT Press, Cambridge, MA/London (1981) Hockey, T.: The Biographical Encyclopedia of Astronomers. Springer, New York (2009) Rousseau, P.: Man’s Conquest of the Stars. Jarrolds, London (1959)

Chapter 14

The Eagle-Eyed Reverend William Rutter Dawes

Many astronomical observations are useful for only a few years before they are completely superseded by new ones. This is especially true in fields that rely on instruments developed with rapidly changing technology. In marked contrast, the best visual measurements of moderately close double stars made 100 to 150 years ago are still good by modern standards. The measurements by Wilhelm Struve, E. Dembowski and W. R. Dawes are valued highly by today’s calculators of binary star orbits.

Thus wrote Dr. Joseph Ashbrook, former editor in chief of Sky & Telescope magazine in a short essay on the life of William Rutter Dawes (1799–1868). Using small classical refractors, made with just a token nod to optical theory, this benevolent English observer greatly advanced our knowledge of the heavens, showing that, above all, acute and highly trained eyes could see things other amateurs could not, even using larger instruments. Born on March 19, 1799, Dawes (Fig. 14.1) could be said to have had astronomical blood in his veins. His father, William Dawes the Elder (1762–1836), served as the astronomer on Governor Philip’s first expedition to Botany Bay, Australia, in 1787 on board HMS Sirius. By the time young William was born, his father had taken up a post as a mathematics master at Christ’s Hospital’s school for boys. The elder Dawes had a strong moral compass, though. Among many other things, he was an outspoken abolitionist. Perhaps this is why the elder Dawes entertained very different aspirations for his son, whom he wished to enter the clergy of the Church of England. Young William was unmoved at first by his father’s wishes, deciding instead to train as a physician at St. Bartholomew’s Hospital in London. It was only after Dawes obtained his medical degree and moved to Liverpool, in or around 1827, do we see a blossoming of his interest in astronomical topics, especially double stars. Writing many years later to his friend, Sir John Herschel, Dawes recounted how he got the double star bug: Having obtained the loan of a volume of Ree’s Encyclopaedia, I had copied out the list of Sir Wm. Herschel’s Catalogue’s of Double Stars, arranged in classes and constellations; This essay is dedicated to Peter Huesmann. © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_14

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Fig. 14.1  The Reverend William Rutter Dawes (1799–1868). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Dawes_William_ Rutter.jpg)

and [using] a capital little refractor of 1.6 inches aperture, and a copy of the French edition of Flamsteed’s Atlas, which was presented by Dr. Maskelyne to my father …. I worked away on almost every fine night, when uncertain health would permit, and found and distinctly made out …. Castor, Rigel, Epsilon 1 and 2 Lyrae, Sigma Orionis, Zeta Aquarii and many others, of which I made correct diagrams in a book now lying before me …. The difficulty was often to get to bed in summer before the Sun extinguished the sight of the game.

While in Liverpool, Dawes came under the influence of the writer and theologian Reverend Thomas Ruffles, who provided pastoral care for the George Street Congregational Church for nearly half a century. Seeing no conflict between his faith and his inspirational work as a double star astronomer, Dawes re-trained as a minister, and upon qualifying, he took charge of a small congregation of the same denomination in the town of Ormskirk, Lancashire, situated about 15  miles north of Liverpool. It was at Ormskirk during the 1830s that Dawes made the acquaintance of William Lassell (who was also a congregationalist), who lived just a few miles away, with the two men exchanging books on astronomy, observing notes as well as testing telescopes. This was well before either man rose to the status of ‘Grand Amateur.’ Dawes was fully 30 years old when he found the time to resume his passion for astronomy, acquiring a fine equatorially mounted 3.8-inch Dollond achromat of 5-foot focus to which a wire micrometer had been affixed. As luck would have it, the instrument and a measure of its achievement is described in good detail in George Bishop’s book, Astronomical Observations Taken at the Observatory South Villa, Inner Circle, Regent’s Park, London, during the years 1839–1851: The instrument appears to have been one of first rate excellence, as shown by the work performed with it, such objects as Zeta Cancri, Zeta Bootis and Mu Bootis, being well separated. In observing the angle of position, Mr. Dawes placed the stars between the parallel

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Fig. 14.2  A classic Dollond of 5-foot focus. With an instrument like this, Dawes honed his skill as one of the finest double star observers in history. (Image by the author) threads – a method suggested by Sir John Herschel – and since very generally adopted. A red illumination of the field was thought to be advantageous. The magnifying power at first employed was 225, but 285 was afterwards substituted as a working power: others as high as 625 being used for very close and bright objects. The observations were almost invariably near the meridian. The most interesting objects are specified in the important contribution to double star astronomy, taken as they were, by one whom John Herschel has styled observer in this particular branch that Europe affords. The catalogue includes more than 400 sets of measures.

Let’s look more closely at Bishop’s remarks. The telescope operated at a ‘working power’ of 285 and could be pushed as high as 625x for ‘very close and bright objects.’ These are magnifications that range from 75x to 165x per inch of aperture! In my study of other small classical refractors, as well as my own personal experience with a lovely 80-mm achromatic doublet of 1200-mm focal length, this author can personally vouch for the soundness of these amplifications in the pursuit of difficult binary and multiple star systems. These simple but highly effective instruments soak up tremendous magnifications, a sure sign of their optical excellence as well as their superior thermal properties (Fig. 14.2). During the early 1830s, Dawes conducted over 600 measures of doubles with his little Dollond and in so doing introduced some refinements to the techniques that were commonly employed at the time, and which made his work more accurate than his esteemed contemporary, Sir John Herschel. A notable advancement in this regard was the introduction of a Barlow lens to increase the magnification without increasing the apparent thickness of the micrometer threads. Another innovation introduced by Dawes involved the employment of a prism diagonal to render the apparent orientation of the line of intersection of two wires either horizontal or ver-

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tical, which helped reduce errors in measuring the star’s position (a bearing- like, 360-degree scale, measured anti-clockwise from north). His exemplary work as an amateur came to a rather abrupt halt towards the end of the 1830’s, when his first wife, Mary Scott, the widow of his former tutor, being considerably older than him, fell ill. He nursed her night and day and could not attend his flock, causing him to relinquish his pastoral duties at Ormskirk. After Mary died in 1838, Dawes was in need of employment, and to that end accepted a post as assistant astronomer at the residence of the tycoon George Bishop, who erected a lavishly equipped observatory (as was his philanthropic duty as a noble) at his home in Regent’s Park, London, after his retirement at age 50. There Dawes would put his world-class skills as an observer to good use. And it was here also that Dawes met his second wife, a widow of Mr. John Welsby, whom he married in 1842. Dawes remained at the South Villa observatory for 5 years as a salaried observer between 1839 and 1844. A successful international wine merchant (indeed, according to research conducted by Dr. Allan Chapman at Oxford University, Bishop’s products amounted to about half of the entire British wine excise tax), Bishop amassed considerable wealth. At age 45 he joined the RAS and, as was his civic duty, founded an observatory with which he might put some of his great wealth to some practical use. Back in 1836, Bishop had erected a fine 7-inch refractor (by Dollond) near his residence at South Villa. Bishop was also eventually elected a FRS member. He was only too delighted to have the by-now famous double star astronomer join his establishment. Like Dawes’ smaller instrument, the 7-inch Dollond is vividly described in Bishop’s aforementioned book: The telescope had a clear aperture of 7 inches and a focal length of 10.75 feet. The tube is of brass, and has been covered in a coating of paint for the sake of preservation. The mounting, generally, is similar to that of Captain Smyth’s equatorial now at Hartwell House, and has been found to answer extremely well. The polar axis is formed of four slabs of mahogany, braced together by strong iron screws; its length is 13 feet, and its breadth in the broadest part (which is near the middle of its length is 9 inches …. The clock-driven movement of the equatorial, an indispensable appendage, also by Mr. Dollond, is firmly attached to a stone pillar …… The eyepieces attached to the telescope magnify respectively 45, 70,108, 200, 320, 460,700 and 800 times. There is a polycratic wheel containing six magnifiers, the highest of which is 1200. One of the greatest conveniences in the measurement of double stars has been found to be the equatorial reclining chair. It was constructed by an ingenious mechanic …. The chair is of mahogany, with brass wheels and fittings. It is attached to the floor of the room, and revolving on an iron pivot, can be brought into any position that may be required.

Over the next quarter of a century, the post of assistant astronomer was to be filled by other well-known observers, including J. R. Hind, Albert Marth, Eduard Vogel, C. G. Talmage and Norman Pogson. Things went swimmingly for Dawes under the aegis of Bishop, during which time he pursued double star mensuration with singular gusto. After that time, the relationship between Dawes and Bishop began to deteriorate, as his employer (a non-astronomer) attempted to pass off many of the observations made by Dawes as his own. But in marrying a well-to-do widow, Dawes found a way out of the situation without causing further conflict between himself and Bishop.

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In 1844, Dawes was able to leave the employ of Bishop and take up residence in a grand country house near Cranbrook in Kent, a site very near where his old friend, Sir John Herschel, had long since put down roots. Here, he erected his own observatory, equipping it at first with a 6.3 inch Merz & Mahler equatorial refractor in 1846. With this fine instrument by the standards of the day, Dawes put his back into double star and planetary work. But he never stayed at Cranbrook for long, though, moving his observatory to his newly acquired premises at Wateringbury, near Maidstone, Kent, and also at Haddenham, Aylesbury, in the county of Buckinghamshire. By 1850, Dawes super keen eyes had independently discovered the Crepe ring of Saturn. Across the Atlantic, the American astronomer, W. C. Bond, using the 15-inch refractor at Harvard College Observatory, had spotted it on the nights of November 11 and 15, 1850. William Lassell, with his large 24-inch speculum mirror telescope, had failed to see it under conditions that he himself described as an “excellent night of November 21.” But Dawes had success with the much smaller Merz & Mahler refractor on the evening of November 25. “I detected for the first time a light within the ansa of the ring at both ends while examining the planet with my Munich refractor of 6.3 inches aperture,” he wrote. On December 3, 1850, Dawes showed the Crepe ring to Lassell in person, and while he did concede that it was visible through Dawes’ long focus achromatic, he was not quite prepared to admit that it escaped his notice in his own larger telescope. Later, though, Lassell did manage to see the Saturnian novelty many times with his large telescope. Genius really is the art of seeing the obvious! Having long abandoned the fickle behavior of the earliest reflectors, the experience Dawes garnered with the 6.3-inch Merz  – its sheer superiority in resolving power over the smaller Dollond  – convinced him that bigger really was better. Predictably, Dawes became an enthusiastic serial collector of ever larger and more powerful refractors. He embraced the promising new telescope maker in the United States – Alvan Clark – ordering a 7.5-inch Clark in 1854 after the maker reported that the dim companion to the star 95 Ceti had been discovered. And in 1859 Dawes acquired an even larger 8.25-inch Clark. With these fine instruments, Dawes was able to extend his tally of double star measurements to 2800. This vast treasure of field experience allowed him to derive an empirical relation between the aperture of a telescope and its ability to resolve tight stellar pairs. In a curious development, published in Vol. 35 of the Memoirs of the Royal Astronomical Society (1867), Dawes penned the formula that was to make him famous: It is a point of considerable interest to determine the separating power of any given telescope aperture. Having ascertained about five and thirty years ago, by comparisons of telescopes of very different apertures, that the diameters of star disks varied inversely with the diameter of the aperture, I examined with a great variety of apertures a vast number of double stars, whose distances seemed to be well determined, and not liable to rapid change, in order to ascertain the separating powers of those apertures, as expressed in inches of aperture and seconds of distance. I thus determined as a constant, that a one-inch aperture would just separate a double star composed of two stars of the sixth magnitude if their central distance was 4”.56; – the atmospheric circumstances being moderately favourable. Hence, the separating power of any given aperture, a, will be expressed by the fraction 4”.56/a.

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Dr. Ashbrook, commenting in his short essay on Dawes in his Astronomical Scrapbook, expressed this view of Dawes’ famous relation: “While this formula is very familiar to amateurs today, its narrow range of validity is often overlooked. Determined with small refractors and Dawes’ eye, the law does not tell what another observer can see with a large reflector or a catadioptric.” In light of ongoing studies conducted by amateurs using both contemporary refractors and high quality reflecting and compound telescopes, it appears that the Dawes’ limit is still a formidable resolution limit for many double star observers. Ashbrook conveys the impression that ‘modern telescopes’ ought to reach this limit owing to advances in optical technology, but intriguingly, this author has thus far obtained evidence that achromatic refractors – both large and small – can exceed these resolution limits by a small margin, and that, visually at least, reflectors (and by implication compounds) can also reach these limits in field tests. Indeed, it can be shown that a large central obstruction can resolve point sources slightly smaller than the classical Dawes limit owing to its ability to shrink the size of the Airy disk. That said, it need not necessarily imply that greater resolution feats on equally matched binary systems cannot be attained. One problem with the Dawes limit is that it is closely associated with an ‘optimized’ wavelength of 562 nm. Yet, the dark adapted eye is optimized at a significantly shorter wavelength of 510  nm, corresponding to an approximately 10% increase in angular resolution. Indeed, this author has suggested that red-green color blind individuals could conceivably resolve even finer pairs. Certainly, images conducted by noted UK imager Damian Peach has clearly shown how angular resolution is inversely related to wavelength by means of using color filters. Furthermore, previous work had suggested Dawes himself was able to exceed his own limit using at least one of the instruments he used to carry out his double star measurements. In addition, there are several sources in the literature that suggest that faint pairs consisting of early spectral type components (O, B and A) can be resolved beyond the Dawes limit. In light of these revelations, one must tread very cautiously indeed in declaring some sort of universal ‘law’ on the resolution limits of a given individual and telescope aperture. Though Dawes became independently wealthy later in his life, corresponding regularly with many of the astronomical elites such as Sir John Herschel, Richard A. Proctor and Admiral W. H. Smyth, he gave up much of his valuable time in the service of the local community, providing them with free medical care and regularly visiting the eldest and most vulnerable members of his congregation. According to his great nephew, the Reverend Arnold Taylor, Dawes enjoyed the company of animals, particularly dogs and horses, which he kept as pets on his estate. Many tales abound of his special relationship with canines, including one that suggests he understood them in unusual ways. One day, while on one of his house visits, he came across a ferocious guard dog that had been chained to its kennel. And though he was duly warned to keep a safe distance from the angry beast, Dawes walked up to it, stared into its eyes and forced it to retreat. Then, the man o’ the cloth dragged the cowering dog from its kennel, petted and made friends with it! Dawes suffered bouts of ill health throughout his life, including migraines, asthma and the chronic symptoms of ischemic heart disease. Yet despite this mal-

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aise, he went about his astronomical work with great diligence. Sometimes he would be found fast asleep in his observatory chair, the great equatorial having swung to a completely different part of the sky. In 1857, he and his wife left Cranbrook and moved to a charming estate in Haddenham, Buckinghamshire, where he was to live out the remainder of his life. After his second wife died in 1860, he only had the company of his retriever to tag along with him on his daily stroll to his observatory. Despite rapidly failing health in his autumn years – which was, by now, compounded by deafness also – he continued to make observations of the bright planets and double stars. In 1865, the Royal Astronomical Society awarded him its highest accolade – the Gold Medal – for his services to astronomical knowledge. On the morning of February 15, 1868, he passed away, nearing the start line of his 70th trip around the Sun. The life of William Rutter Dawes remains an inspiration to those who see harmony between religious faith and scientific advancement. As a Christian, he had a duty to seek wisdom from the book of Scripture and as an astronomer from the book of Nature.

Sources Airy G.B.: Address delivered by the Astronomer Royal on presenting the Medal of the Society to the Rev. William Rutter Dawes. http://adsabs.harvard.edu//full/seri/MNRAS/0015//0000148.000. html Ashbrook, J.: The Astronomical Scrapbook. Cambridge University Press, Cambridge (1984) Bishop, G.: Astronomical Observations Taken at the Observatory South Villa, Inner Circle, Regent’s Park, London, During the Years 1839 to 1851. Nabu Public Domain Reprints, LaVergne (2012) Chapman, A.: The Victorian Amateur Astronomer. Gracewing, Leominister (2017) Denning, W.F.: The Rev. William Rutter Dawes. http://adsabs.harvard.edu//full/seri/ Obs./0036//0000419.000.html Tebbutt, J.: Observations of the Solar Eclipse of 18th Aug. 1868. http://adsabs.harvard.edu//full/ seri/MNRAS/0029//0000116.000.html Warner, D.J.: Alvan Clark & Sons, Artists in Optics. Smithsonain Institution, Washington, DC (1958)

Chapter 15

The Telescopes of the Reverend Thomas William Webb Brief Biographical Details

Working for work’s sake, and that from the highest motives. – T. H. E. C. Espin

Thomas William Webb (Fig. 15.1) was born on December 14, 1806. However, it is noteworthy that in Reverend Epsin’s “A Reminiscence,” in the introductory pages of Celestial Objects for Common Telescopes [1962], his birthday is quoted as December 14, 1807, in the county of Hereford, England. He was one of two children to his parents, the Reverend John and Sarah Webb. The elder child, a girl, Anne Frances (born 1801), died tragically when Thomas was just a few years old, and he thereafter remained an only child. Thomas’ mother, who had long struggled with mental and physical illness, was unable to provide the usual maternal guidance to her son. Some sources state that she died when Thomas was just a boy, but in fact she survived to see her son marry and finally gave up the ghost in July 1849. It is difficult to gauge how Thomas dealt with his mother’s mental health issues. Perhaps the pain he felt made him somewhat upset or ashamed (a typical Victorian attitude), thus explaining why he rarely spoke about her. Breaking with the tradition of the time, young Thomas was home schooled by his father, together with a few other children from the local gentry, who instilled in him a great and abiding reverence for the workings of the natural world. His was a classical education; mastering mathematics, the natural sciences, ancient history, Latin, German, French and even some Hebrew. Such an upbringing made him a prolific maker of notes, preternaturally curious and studious – attributes clearly in evidence from the voluminous literature he left behind to posterity. In 1826, Thomas entered Magdalene College, Oxford, and received a second class honors degree in mathematics in 1829. While at Oxford, he also studied divinity and was ordained an Anglican minister in the same year. In 1843, he married Henrietta Montague, a woman he later described as “having rare gifts and a most generous heart.” The marriage was a happy one but, sadly, childless. Henrietta died of apoplexy (a stroke) on September 7, 1884, which dealt Webb a severe blow. The following year, his health failing rapidly, the Reverend T. W. Webb passed away on © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_15

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Fig. 15.1  The Reverend T. W. Webb (1807–1885), from the cover plate in the 1917 edition of Celestial Objects for Common Telescopes. (Image courtesy of Wiki Commons. https://upload. wikimedia.org/wikipedia/ commons/1/14/TWWebb. jpg)

May 19. According to Dr. Allan Chapman from the University of Oxford, Webb’s estate was valued at £16,986, indicating his considerable personal wealth that would have easily allowed him to pursue the typical career of a Victorian Grand Amateur. Yet, as we shall see, that was not the path he chose in his pursuit of astronomy.

Early Telescopic Forays Webb’s first recorded astronomical observation was of a meteor he spotted on the evening of January 5, 1818, when he was just 11 years old. Just a few weeks later, he made observations of the Moon with telescopic aid. What is clear is that Webb had access to a variety of small astronomical telescopes, lent to him by friends of the family. The first identified telescope owned by Webb was a small 1.3-inch refractor by Bates, which he made use of in the early 1820s. But by this time, he was dabbling in making his own optical devices, mostly small speculum metal mirrors of 3–6 inches in aperture. Though he endured many failures in casting good speculum mirrors, he finally achieved success in 1827, where his diary entry, dated September 9, showed that he had managed to make “a small Newtonian with fixed specula and eyepiece… extremely satisfactory and immensely improved, seemed to bear a power of 60 or 70.” Over the coming months, Webb was able to make further improvements to the instrument, finally exclaiming with some excitement on August 23, 1828, that. “….my telescope is a superior one by Herschel’s own tests!!!” The 1820s marked a crossroad in astronomical instrumentation. The achromatic refractor, employing a doublet objective of crown and flint glasses was, with very

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rare and notable exceptions, confined to small aperture telescopes (rarely in excess of 4 inches) because of the difficulty of obtaining sufficiently high-quality glass blanks that were free from bubbles and striae. This led to vigorous researches into devising other means of overcoming these technological problems. Two avenues of research were pursued: the dialyte and the fluid lens. In the late 1820s, A. Rogers proposed using a full-sized crown singlet coupled to a smaller piece of flint glass placed well back in the focal plane, with the result that adequate achromatism could be obtained. Rogers managed to focally retro-couple a 3-inch flint lens with a 9-inch crown object glass of 14-foot focus. Around about the same time, other amateur astronomers considered using liquid lenses. Organic fluids such as carbon disulfide were deemed particularly suitable, owing to their perfect transparency, relative stability and high refractive index. Webb actually built and used a telescope with a liquid lens for 4 years between 1830 and 1834 and to good effect. That being said, neither the dialytic nor the liquid lens refractors achieved much in the way of popularity. In much more recent times, the late British inventor, John Wall (1932–2018), the poorly acknowledged inventor of the Crayford focuser, managed to construct a 30-inch dialyte, making it the largest refractor in Britain. In the summer of 1834, Webb’s father purchased a ‘capital telescope‘for his son, built by the younger Tulley, with a 3.7-inch doublet object glass and a focal length of 5 feet (f/16). The instrument duly arrived on July 3, and by July 22, Webb had subjected it to “a thorough trial, to do which I sat up, & knelt down in the gravel path till past 1. The result was most and completely unexpectedly satisfactory….for very little did I think I had got a first rate instrument when I received it.” (Fig. 15.2). Fig. 15.2 Webb’s ‘common telescope,’ the 3.7-inch Tulley refractor. (Image by the author)

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Remarkably, this telescope was to be Webb’s main instrument for the next 24 years and served as the ‘common telescope’ he used to compile his now universally lauded Celestial Objects, first published in the same year as Charles Darwin’s Origins (1859). Using his Tulley achromatic, Webb carried out unsystematic observations of the solar photosphere, the Moon and the major planets, double, multiple and variable stars, as well as the brighter deep sky objects. Ever since 1844, Webb had been enthralled by Admiral W. H. Smyth’s A Cycle of the Celestial Objects, a masterful survey of the night sky conducted with a substantially larger (and not at all common for the era) 5.9-inch refractor also by Tulley. Although Webb openly acknowledged the greater suitability of Smyth’s Cycle to the most advanced amateurs, he (correctly) surmised that his work would be better served by what could be achieved with a smaller telescope. We can glean some information on the optical performance of the 3.7-inch Tulley refractor by exploring how well it performed on double stars he observed in compiling his Celestial Objects. The Dawes limit (expressed in seconds of arc) for such an instrument is 4.56/D, where D is the diameter of the object glass (in inches). This yields 1.23″. Double star astronomer R. W. Argyle, based at the Institute of Astronomy, Cambridge, found that Webb noted that both Zeta Cancri and Sigma 1517 Leonis were slightly elongated (both 1.0″ splits in 1849 and 1851, respectively), while Sigma Canis Majoris had ‘discs in contact’ (1.3″ in 1856). These data indicate that the Tulley refractor Webb used for nearly a quarter of a century was operating at or very near its theoretical resolving power.

The 3.5-inch Triplet Dollond Achromatic Apart from the instruments he owned outright, Webb lived at a time where there was a culture of sharing instruments among a large circle of friends and astronomical acquaintances. We know that Webb also borrowed at least one other instrument – a 3.5-inch Dollond refractor with a triplet objective. First constructed back in 1771, it had a focal length of 44.5 inches (relative aperture 12.7) and was purchased by William Wollaston, who then passed it down to his son, William Hyde Wollaston. In turn, the younger Wollaston bequeathed the instrument to the Astronomical Society of London (later the Royal Astronomical Society) in 1828. Wollaston stipulated that the instrument should not gather dust but be lent to “some industrious member.” Wollaston achieved his aims, and the instrument was used by a succession of observers, finally arriving at Hardwicke (then Webb’s parish and place of residence) in 1856. It is difficult to see how the 3.5-inch Dollond would be of any advantage to him over his (larger) Tulley refractor. Indeed, he later expressed some degree of ambivalence about this telescope. In a letter dated January 5, 1857, to the secretary of the RAS, Webb said of the Dollond triplet, “I cannot pronounce it first rate” but later said in his notes that the same instrument was “very fine against my Tulley, and though there is no very wide discrepancy, I think mine beats it.”

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It may be of interest to the reader that the self-same Dollond triplet was subjected to a more thorough optical assessment by the famous British optician, Horace E.  Dall, in 1980. His report showed that the instrument had a few small errors mainly related to stress-induced astigmatism, owing to slight warping of the lens elements arising from over-tight mounting inside its lens cell. The instrument is now exhibited in the Science Museum, South Kensington, London. Although one might expect an observer who became so intimately acquainted with a small achromatic refractor, using it regularly over the course of nearly a quarter of a century, might have held on to it for sentimental purposes, it is interesting to learn that in January 1858 Webb sold his Tulley, making temporary use of a smaller refractor by Bardou, which belonged to his wife, Henrietta, and which had an aperture of just 2.2 inches and a focal length of 27.8 inches. But a few months later, Webb took delivery – no doubt on the recommendation of his friend, the Reverend William Rutter Dawes – of a 5.5-inch object glass of 7-foot focus made by the talented American telescope maker, Alvan Clark of Cambridge, Massachusetts. After it finally arrived in June of 1858, Webb employed joiners in Birmingham to make a tube for it, but having seen their shoddy workmanship, immediately sent it back to them. By September of that year, he had made his own makeshift tube to assess the quality of the American object glass: “First Trial of the Great Object Glass by Alvan Clark, 5.5 inches clear aperture, fitted up temporarily in an old square deal tube. Its performance, in the utter absence of centering, appeared to be admirable.” In another note made in 1859 he claims that having examined the images of Zeta Cancri through Admiral W. H. Smyth’s 5.9-inch Tulley refractor, Webb judged this famous instrument to “appear inferior to my own’ [Clark].” A year passed, but Webb still did not secure a suitable tube to mount to the Clark object glass. Why he didn’t is somewhat of a mystery. Perhaps he was having second thoughts about dealing with such a large and cumbersome telescope? In addition, the optical tube would have required a very substantial mount. We see other clues as to why Webb delayed resolving these problems. The great telescopist always observed in the open air and from the serenity of his own garden. He never had an observatory, like many of his gentleman astronomer chums. Perhaps he found that a long focus 5.5-inch Clark might simply have been too large and unwieldy an instrument to use regularly in the field. J.  C. D.  Marsh in The Stargazer of Hardwicke; the Life and Work of Thomas William Webb, offers us further insight: “Webb was certainly aware of the micrometric work being carried out by Dawes, Smyth and others, and he would certainly have been able to afford a large telescope and micrometer had he so wished.” Marsh goes on to cite other reasons for his avoidance of that particular modus operandi, including the demands of his clerical duties and his deteriorating eyesight owing to advancing age. But it may have been the ‘general’ or ‘non-specialized’ nature of his observing practices – wandering from the endless delights of the Moon to a bright planet and onwards to an auspicious cometary interloper, and from there to the far distant stars – that might have given him pause to follow the paths of his closest astronomical acquaintances. Compared with many of his peers, Webb was a

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‘jack of all trades’ observer, uncommitted to any particular astronomical cause. His was a spirit more than happy to get lost in the glories his little telescope presented to him. For example, take this excerpt from the section on Cygnus in his Celestial Objects: “I had at one time conducted a survey of the wonders of this region with a sweeping power, but want of leisure, an unsuitable mounting, and the astonishing profusion of magnificence, combined to render this task hopeless for me, which, I trust, may be carried through by some future observer.” Whatever the reasons, we do know that Webb‘s interest in refractors waned somewhat as he heard word of new technology that was sweeping the British amateur community during the 1860s. Still, Webb still  made occasional  use of his ‘makeshift‘Clark achromatic, observing a variety of objects, including the exploration of the Great Comet of 1861 (1861 J1), where his surviving drawings show clear evidence of jets and dust shells reminiscent of recent comet apparitions, such as Hale-Bopp or Hyakutake. Ever since the first reflecting telescopes were made in the late seventeenth century, astronomers had used speculum metal (an alloy of mostly copper and tin) for their mirrors. But these had many issues. For one thing, metal is difficult to grind and figure into the required parabolic shape necessary to get the best images. It had a reflectivity of only 68% at 450 nm (blue) rising to 78% at 650 nm (red). However, when exposed to the elements, it tarnished rather quickly, losing an estimated 10% after just 6 months in the damp British air. Removing the mirror for polishing also changed its figure, requiring a complete regrinding of its surface. Furthermore, because of the high density of speculum metal, even fairly small mirrors were very heavy and cumbersome to mount. All these issues impelled a number of scientists to redouble their efforts to look for better ways of making telescope mirrors and, accordingly, experiments were set up to establish whether substances such as silver could be deposited onto glass substrates. In 1855, the great German chemist, Justus von Liebig, produced metallic surfaces refined enough to use in optical devices but never applied it directly to telescope mirrors. Within a year of Liebig’s findings, though, C. A. von Steinheil in Germany and Leon Foucault in Paris had independently demonstrated that silver could be deposited on a pre-figured glass substrate, the latter producing a fine speculum some 20 inches across. This was the game changer astronomers had wished for, because it suddenly made available large glass-based primary mirrors that maintained their reflectivity longer and could easily be re-silvered and polished as and when required. What’s more, because these silver-on glass mirrors were much cheaper than the lens-based object glasses that dominated until then, many more amateurs could afford to acquire them. By 1859, the British amateur astronomer, Reverend Henry Cooper Key, succeeded in fashioning a fine 12-inch f/10 mirror and shortly afterwards produced an 18.25 silver-on-glass mirror with a focal length of 11  feet. After publishing his methods, Key’s work came to the attention of George With (1827–1904), who managed to make four such mirrors ranging in aperture between 5 and 6.5 inches. With also corresponded with Webb and supplied him with a 5.5-inch silver-on-glass mirror that he subjected to tests.

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In August 1863, Webb wrote to the secretary of the RAS informing him that he had “a 5.5 inch silvered Newtonian on trial … and it does its duty well. I think it must be fairly equal to a 4-inch achromatic or more & he will yet, I am persuaded, do better yet.” Soon after, another British mirror maker came to the fore  – a young George Calver (1834–1927). Calver’s appetite for astronomy was whet after his local vicar, the Reverend Matthews of Great Yarmouth, showed him some of the splendors of the heavens through his newly acquired silver-on-glass reflector with a mirror supplied by With. Matthews is said to have set a challenge to Calver to see if he could make a mirror as good as the one he had in his possession. Luckily, Calver accepted the challenge and soon found himself hard at work, fashioning, gifting and selling his own specula. England now had three choice mirror makers, and amateur astronomy across the country flourished. A quiet revolution was underway. In 1864, Webb purchased an 8-inch mirror from With, but there are not many surviving records of him using it. However, in 1866, Webb’s father (then aged 90) bought a larger telescope for his only son, a 9.25-inch f/8 Newtonian reflector (Fig. 15.3) on an ‘equestrian’ mount manufactured by the Reverend Edward Lyell Berthon (1813–1899). This was to be Webb’s final and largest telescope that he would use regularly for the last two decades of his life. Owing to the large size and massive mounting of the With-Berthon Newtonian, Webb was compelled to change his observing habits; no longer could he observe in Fig. 15.3  Webb’s 8-inch Newtonian with optics made by George With. (Image courtesy of D. Buczynski. Used with permission)

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the open air freely, like he had done for decades. He would have to build an observatory of sorts for his new instrument. With a large number of astronomical friends and acquaintances to call upon, Webb had many architectural genres to choose from. He could lavish huge sums on a brazen, domed observatory, like those erected by the Reverend Dawes at Haddenham, Buckinghamshire, or the tycoon, George Bishop, in the Inner Circle of Regent’s Park, London. Instead he went for the much more economical Romsey-type observatory (shown below), so named because it was first devised by E. L. Berthon in his home parish of Romsey and was constructed relatively cheaply and quickly from wood, with a rotating canvas roof. It was situated a few yards south-southeast of the vicarage and served its purpose perfectly well for over 15 years, when it began to show its age all too easily. In a letter to Arthur Ranyard, dated February 2, 1883, Webb confessed: “My telescope roof is all to pieces. I’ll put on another roof with two pairs of opposite shutters, not only saving time in turning, but as the one side rises more steeply than the other, giving relief in position where now it cramps the head awkwardly. There was a bright thought.” (Fig. 15.4). The optical quality of his 9.25-inch With-Berthon reflector was undoubtedly excellent, as judged by the many exquisite drawings of the Moon and planets he left behind in his notebooks. Webb achieved a clean split of Eta Coronae Borealis, which, at the time, had a separation of 0.55″ – satisfyingly close to the Dawes limit for such an aperture (0.5″). In addition, his 9.25-inch speculum resolved Gamma 2 Andromedae at powers of 225×. Webb also reported seeing marked elongation in

Fig. 15.4  Denis Buczynski inspects the With/Berthon reflector (BAA# 83) at his home in Lancaster. (Image courtesy of D. Buczynski. Used with permission)

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Fig. 15.5  A ‘Romsey-­ type’ observatory. (Image courtesy of D. Buczynski. Used with permission)

Omega Leonis (0.52″ in 1878). This provides further evidence that when properly executed, Newtonian reflectors could be very effective double star splitters (at least for near-equal magnitude pairs). This also dovetails well with this author’s ongoing observations with modern 8-inch f/6 and 12-inch f/5 Newtonians (Fig. 15.5). Webb discovered 10 new double and multiple stars mostly with his 9.25-inch reflector, its considerable light-gathering power doing especially well with wide and faint companions. He did not conduct measurements on these systems, leaving that delicate work to more specialized double star observers, such as S. W. Burnham, W.  R. Dawes and Baron Dembowski, who employed large and well mounted refractors. Veteran BAA member Denis Buczynski said this about the telescope’s history after Webb passed away: ‘Webb was a friend of George With,’ he explained, ‘and I am sure he sky tested mirrors for With. Webb used a 9-inch f/8 on a Berthon equatorial, an unusual mount. The BAA mount was not a commercially produced mount, it was a one off. It was a cast iron pedestal tilted to accept a polar disc (this disc was made of slate covered by a circular sheet of brass), containing four brass rollers and the half circle which held the declination circle. The declination axis was in the plane of the polar disc above two of the rollers and held two curved arms which connected to the tube and also supported the steady rods. The mirror was ­definitely a With and was signed by him accompanied by a Latin inscription [Withus Herefordensis me ad astra investiganda fecit]. The only commercial mounts sold as ‘Berthon’ were made by Horne and Thornthwaite. The BAA mount was not one of them. I asked Horace Dall about the small discrepancy between the two sizes Webb had quoted for his telescope (9.00 and 9.25 inches), but he did not consider it significant. He said the quoted aperture was sometimes measured from the very edge of the mirror and sometimes from the interior of the edge chamfer. Also it was possible that Webb had in his possession

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more than one 9-inch mirror from With. After Webb’s death, his instruments were passed onto the Reverend T. Espin (who edited later editions of the ‘Celestial Objects’) at Tow Law, near Durham. After Espin’s death in 1935, the observatory at Tow Law continued to be operated by William Milburn, who was Espin’s assistant. In 1938 Milburn offered the Webb 9-inch for sale in an advert in the JBAA. The BAA accepted the donation of instrument 83 in the late 1940’s from Charles Waller. It is very possible that Waller had purchased the 9-inch from Tow Law, and then it was eventually donated to the BAA ten years later. The link between Tow Law and Waller is the only link needed to firmly establish that BAA instrument number 83 was the 9-inch With reflector used by Webb.

In the late 1970s and early 1980s, Buczynski used Webb’s With-Berthon as his main lunar and planetary telescope, having had both mirrors re-aluminized. He was kind enough to provide some drawings he made through it (shown below). He also confirmed that the optical figure on the mirror was first rate, as was another 18-inch With mirror tested by Buczynski and used by Nathaniel Green, which we will discuss more fully in the next chapter (Fig. 15.6). There are some subtle differences between the images used in modern Newtonian reflectors that employ aluminum as compared with their silvered counterparts. This is best illustrated by means of a graph showing how the reflectance varies with wavelength. Specifically, silver absorbs blue wavelengths much more strongly than aluminum (see Fig. 15.9). Thus, objects would be appear to be slightly red enhanced in the silver-on-glass reflector, while modern aluminum-coated mirrors would be better color balanced (perfectly achromatic) (Fig. 15.7).

Fig. 15.6  An edge-on Saturn as drawn by D.  Buczynski using Webb’s 9 .25-inch speculum. (Image courtesy of D. Buczynski. Used with permission)

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Fig. 15.7  Jupiter as recorded by D. Buczynski using Webb’s large Newtonian. (Image courtesy of D. Buczynski. Used with permission)

That said, Webb considered his reflector essentially achromatic. In his discussion on telescopes in Volume One of his Celestial Objects, he seems to have grown more partial to the images produced by his specula: An achromatic, notwithstanding the derivation of its name, will show color under high powers where there is much contrast of light and darkness. This ‘outstanding’ or uncorrected color results from the want of a perfect balance between the optical properties of the two kinds of glass of which the object glass is constructed; it cannot be entirely remedied, but it ought not to be obtrusive …. Reflectors are delightfully exempt from this effect; and as now made with specula of silvered glass, well deserved, from their comparative cheapness, combined with admirable defining power, to regain much of the preference which has of late years been accorded to achromatics.

According to science historian, Professor Thomas Hockey, based at the University of Northern Iowa, Webb entered into a long-standing debate concerning the perceived colors evident in the massive Jovian atmosphere. Specifically, one issue raised was the relative fidelity of the Jovian image garnered in achromatic refractors compared with those derived from the then (relatively) novel silver-on-glass reflectors (Fig. 15.8). Blue light is led astray in the achromatic doublet but was absorbed by the silver and has an ‘overabundance’ of red. But which was worse? “Webb finally came out decisively  on the side of the reflector,” writes Hockey, “which, at least, eliminated the blue altogether, rather than producing an annoying blue fringe.” (Fig. 15.9).

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Fig. 15.8  Mars as observed by Buczynski using Webb’s large Newtonian. (Image courtesy of D. Buczynski. Used with permission)

Fig. 15.9  This shows the reflectance of silver (Ag), aluminum (Al) and gold (Au) as a function of wavelength. (Image by the author)

Sources

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A Brief Commentary on Webb’s Notes As was the custom of observers of his age (and which, sadly, has much declined in the modern era), note keeping was an integral part of observing culture. A note-­ maker became a man or woman of letters. His or her observational books and other writings are laconic and factual, containing maxims, often expressed in correct Latin (in contrast to some examples of Admiral W. H. Smyth’s use of the Roman language in his Cycle). Webb paid very close attention to his observing conditions, his writing always neat and tidy. Unlike many other observers, Webb had a fondness for observing star fields; indeed he thought of these as new objects in their own right. He would observe on a Sunday. His notes were most often brief, well organized and not without a sense of humor. Webb published many of his finest works in Nature, its founder and first editor, a one Sir Norman Lockyer, rewarding the diligence of his long-time friend. Throughout his writings we gain many glimpses of his sincerely expressed reverence for the universe around him. For Webb, this reverence did not upwell from any deep understanding of the objects he visited with his garden telescopes. After all, the nature of the many nebulae he observed was not known at the time. Rather, that same reverence was derived from a trenchant sense of ignorance concerning the objects his eyes met with. As Albert Einstein once put it: “The most beautiful thing we can experience is the mysterious!” Despite the growing power of scientific naturalism within later Victorian society, Webb couched everything, with firmness and gentleness, in terms of the Biblical God he believed in. Seen in this light, his astronomical writings, and his devotion to exploring the wonders of Creation with his telescopes, were more like prayers than anything else. In the early twenty-first century, obtaining telescopes like those used by Webb is not difficult, nor necessarily expensive. What Webb’s legacy has shown us is that the kind of telescope one chooses is far less important than what kind of observer one ultimately becomes. Webb’s small refractors, which he used profitably for nearly a quarter of a century, would optically be similar (or inferior) to a modern long-focus achromatic. One can choose from an economical model or one that is more ornate. The same is true for Webb’s large Newtonian reflectors. Choose your telescope, carve your path through the starry wilderness and create your own legacy “til the dappled dawn doth rise.”

Sources Chapman, A.: The Victorian Amateur Astronomer. Gracewing, Leominister (2017) George Calver and some of his Telescopes. http://www.britastro.org/iandi/instrument-93.htm Hockey, T.: Galileo’s Planet: Observing Jupiter Before Photography. Institute of Physics Publishing, Bristol (1999)

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Robinson, J.M. (ed.): The Stargazer of Hardwicke; the Life and Work of Thomas William Webb. Gracewing, Leominister (2006) Rogers, A.: On the Construction of Large Achromatic Telescopes. M.N.R.A.S. 1, 71 (1827) Tolansky, S., Donaldson, W.K: The Reflectivity of Speculum Metal. http://iopscience.iop.org/09507671/24/9/308/pdf/0950-7671_24_9_308.pdf Wall, J.: Building a 30-inch Refractor. J.B.A.A. 112, 260 (2002) Webb, T.W.: Celestial Objects for Common Telescopes Vols One and Two. Dover, New  York (1962)

Chapter 16

The Astronomical Adventures of Artistic Nathaniel Everett Green

Art and astronomy have always been close allies. Sir William Herschel famously quipped that: “seeing to some degree is an art that must be mastered.” The great American lens maker and founder of a telescope dynasty, Alvan Clark, was a portrait painter by profession before he turned his hand to fashioning some of the finest refractors of the 19th century. And across the pond in England, a landscape artist of considerable ability set his hand to recording the surface features of the bright planets in extraordinary detail (Fig. 16.1). Born in Bristol in August 21, 1823, the third son of Benjamin Holder Green (1793–1865), then a haberdasher, and Elizabeth ‘Betsey’ née Everett (1795–1837). Nathaniel Green received most of his formal education from his maternal uncle, a one Reverend C. Green. At age 17, Green secured a job in a merchant’s office in Liverpool, but soon grew disillusioned with the post, where he felt his artistic talents were going to waste. At 21, he decided to enroll as a student at the Royal Academy, London, where he flourished and quickly established himself as a talented  landscape painter. In 1847, he married Elizabeth Goold, who hailed from Cork, Ireland, and shortly thereafter set up home at 39 Circus Road, St. John’s Wood, London, where they remained for the next 49  years. Here Green flourished as a highly sought-after art teacher, with one of his pupils including the young Queen Victoria, whom he tutored at her opulent country residence at Balmoral, Scotland, in 1880. It was not until the late 1850s that Green developed a keen interest in astronomy, and in particular, conducting visual observations of the Moon and bright planets, to which he would lend his great artistic skills. In 1859 he purchased a good 4.5-inch achromatic doublet objective from a reputable French optician and constructed his first telescope with it, which he used to begin his explorations of the planets. Soon he found himself pining for more aperture and acquired a 5-inch refractor followed by a 9-inch reflector in 1872. After that he acquired a fine 13-inch silver -on -glass reflector with optics from the renowned Hereford mirror maker, George With. This instrument had an open tube which facilitated its acclimation (there were no cooling fans in those days). Finally, in 1882, Green secured his largest telescope, an 18-inch silver-on-glass reflector, which he purchased from © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_16

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Fig. 16.1  Nathaniel Green’s Mars map. (Image courtesy of Wiki Commons. https://en.wikipedia. org/wiki/File:Nathaniel_Green_Mars_map_-556069113.jpg)

its previous owner, the Revd Jevon J Muschamp Perry, housing it in one of two observatories he set up in his London garden. He would usually employ powers between about 250 and 560x with the latter instrument, and, owing to the less than idyllic condition of his urban atmosphere, regularly resorted to stopping it down to just 7 inches using an off-axis mask. Being quite well to do, Green had the 13-inch instrument shipped to Madeira on the Portuguese archipelago. Here he could enjoy more frequent clear skies and better conditions, allowing him to more fully exploit the significant aperture increase in his telescope. It was this telescope that Green used to make his now famous study of Mars between August and September 1877. At first, he set up his telescope at a spot some 1000  feet above sea level but also investigated another site a further 1200 feet higher in altitude. Curiously, the latter site proved inferior to the former, which only serves to illustrate that greater altitude does not necessarily conflate with better astronomical conditions. His records show that of the 47 nights he spent at Madeira, 26 were favorable enough for drawing, 10 were passable, 10 good, 4 nights he reported as excellent and two were, in his own words, superb. Using soft pencils, Green recorded remarkable details of the planet, selecting the 12 best from a tally of 41 for publication in the Memoirs of the Royal Astronomical Society, Vol. 44, which was published in 1879. Green employed powers of between 200 and 400 diameters, but most usually he used 250x to make his now famous

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drawings. Green appears to have been the first to observe an active dust storm on the planet taking place over a large swathe of land just south of the Valles Marineris. Unlike his illustrious astronomical contemporaries, who were sketching the Red Planet crisscrossed with canals, Green reported none and even suggested that these were optical illusions. In declaring this, Green became the first visual observer to cast doubt on the reality of these controversial features in strong contradiction to G. V. Schiaparelli in Italy and Percival Lowell in the United States. Furthermore, Green also expressed skepticism regarding the idea that Mars had seas. He writes: “In regarding to the general dark markings on this planet, they are generally considered to be oceans, but if this is the case, should they not exhibit something of a reflection of the Sun’s light when on the meridian.” On scrutinizing his fine drawings, the eminent professional astronomer, Professor James Keeler, wrote: The admirable drawings of Mr. Green owe much of their value to the care which has been bestowed on the appearance of the different features and their agreement with views of Mars with large and small telescopes is doubtless due to the same reason. It seems to me that the habit of representing indefinite boundaries by sharp lines and neglect to a uniform scale of relative intensity are responsible for most of the discrepancies in drawings which are ascribable to personality of the observer in attributing faint markings.

The reader will note that Keeler based his comments on his own observations of Mars with a 13-inch refractor at Allegheny Observatory, Pennsylvania, the same aperture class to that employed by Green. He observed Mars once again with his 13-inch, but this time the observations were made from his garden at St. John’s Wood, London. Alas the conditions were not nearly so favorable there as they had been in Madeira. He wrote: “The definition afforded by the St. John’s Wood atmosphere has barely sufficed to identify the details of the Madeira drawings.” Comments like these reaffirm the importance of location in divining the maximum detail one can extract from a telescopic image. Green made more exceptionally high-quality drawings of Mars during the favorable opposition in 1886, using them to construct an accurate map of the planet’s northern hemisphere. He also made similar high-quality drawings of many lunar features, as well as Saturn and Jupiter with his telescopes that continue to inspire future generations of amateur astronomers. In 1885 alone, Green created no fewer than 156 drawings of these planets at or near opposition, producing especially valuable observations of the Great Red Spot. As one of the founder members of the BAA in 1890, Green was president during the years 1896–98, and for some years also directed its Saturn section. In 1894 the BAA Mars Section Director, B. E. Cammell, produced a manuscript report that was too long for the council to publish. Green was called upon to edit the memoir down to a more acceptable length, and this he did. In 1897, Green presented his 18-inch mirror to the association, and it was later used for many years at Headley Observatory, England, by the Rev T. E. R. Phillips, mostly for observations of Jupiter and Mars. And in more recent years, it was used productively by the well-known BAA veteran, Denis Buczynski, while he was living at Conder Brow, Lancashire.

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Fig. 16.2  The 18-inch reflector used at Headley Rectory Observatory by the Rev T. E. R. Philips. (Image courtesy of Denis Buczynski. Used with permission)

Green continued to remain very active, both as a telescopist and a landscape artist, right into old age. After a busy day of painting, he would relax over a light evening meal and then take to his telescopic work on every clear night. And on cloudy evenings, he’d pursue his other passion; microscopy. In the last decade of his life, he and his wife, Elizabeth, would winter in the milder climes of Cannes, France, to avoid the damp winters of England. Nathaniel Green; artist and astronomer, passed away after a short illness on November 10, 1899, survived by his wife and children (Figs. 16.2 and 16.3).

An Aside: The Many Lives of a Telescope I contacted BAA veteran, Denis Buczynski to learn more about the fate of the 18-inch With reflector owned and used by Nathaniel Green. He writes: It belonged to the BAA and was donated to them after Green died. It was the largest mirror that George With made. The BAA placed it on loan with Rev T. E. R.Phillips at Headley Rectory Observatory where it was used for mainly planetary observations, especially Jupiter up to the outbreak of WW2. All the main BAA observers observed there. It was magnet for them. The telescope (made entirely of wood) originally stood outside. Eventually it was remounted in the dome that contained the 12 inch Calver on the Calver mount but fitted with an open framework tube. It gave wonderful views in this location and dozens of drawings were published in the BAA Jupiter Section Memoirs. After the war years (Phillips died in 1948) the mirror was loaned out again then it was passed on in the 1960's

Sources

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Fig. 16.3  The resurrected 18-inch With reflector at the observatory of Denis Buczynski, Conder Brow in Lancaster. (Image courtesy of Denis Buczynski. Used with permission)

to Peter Cattermole, a mate of Patrick Moore, who was a planetary geologist. He had it for 25 years but did nothing with it. I picked it up from his house in Sheffield in the late 1980s and it was mounted (by David Greenwood) on a huge English Yoke mount made of heavy steel section and had an open framework tube. It was wonderful telescope to look at the Moon and planets with in good seeing it was a joy to see what it could show. Long focus 122 inches 18 inch aperture, fantastic! It was sent back to the BAA about 10 years later in the mid 1990's and is now in the museum at Hereford (where With lived and worked).

Sources Chapman, A.: The Victorian Amateur Astronomer. Gracewing, Leominister (2017) Green, N.E.: Observations of Mars, at Madeira, in August and September 1877. http://articles. adsabs.harvard.edu/full/1879MmRAS.44.123G McKim, R.J.: Nathaniel Everett Green: Artist and Astronomer. http://articles.adsabs.harvard.edu// full/2004JBAA.114.13M/0000020.000.html?high=5981edc12529108 Sheehan, W.: Planets and Perception: Telescopic Views and Interpretations 1609 to 1909. The University of Arizona Press, Tucson (1988)

Chapter 17

Edward Emerson Barnard, the Early Years

There are few stories in the annals of astronomy more endearing than that of Edward Emerson Barnard. Born in the slums of Nashville, Tennessee, on December 16, 1857, Barnard never knew his father, Reuben, who died 3 months before he came into the world. His mother, Elizabeth, herself a native of Kentucky, moved to Nashville in search of work, eking out a meager living fashioning and selling wax flowers. Edward was the younger of two sons, but little is known concerning his older brother by 3 years, Charles, only that he may have had significant learning difficulties. And while childhood is ideally a happy and carefree experience, Edward never looked too fondly on his earliest years. The young nation was engaged in a bloody Civil War and the South was laid waste. His boyhood, he would later divulge, was “sad and bitter that even now I cannot look back on it without a shudder.” Such was the poverty endured by the family that they would often go hungry. Indeed, Edward would later recall a desperate incident in which a steamer, packed with provisions, sunk in the local Cumberland River, causing a frenzy of looting. Some set out in boats to recover the submerged crates of foodstuffs. Barnard dived in, recovering a box of crackers that his mother ground to powder, whipped into batter and made into cakes (Fig. 17.1). Finding some relief from the drudgery of the workaday world was hard, but the young Barnard found it by lying on his back in a simple wagon bed, watching the stars at night. Their peaceful light comforted him. He would note their variation in glory, some exceedingly faint, others brilliant and fiery. Soon, he would greet them like friends. The end of the Civil War brought little relief to Nashville, though, when an outbreak of deadly cholera swept the city, claiming the lives of hundreds of people. Fortunately, young Edward survived, but just barely. In 1866, Elizabeth stumbled across a photograph bearing the name of Van Stavoren, identical to that of a gentleman she had made acquaintance with in Ohio during happier times. It turned out that he had established himself in Nashville as a photographer, and once she found his place of work, she was relieved to see that it was one and same man. Better still, Van Stavoren was on the lookout for a boy who could run errands for him across town as well as operating an enormous solar © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_17

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Fig. 17.1 Edward Emerson Barnard, aged about 9 years. (Image courtesy of Vanderbilt University)

c­ amera he had set up on the roof of his premises on the corner of Union and Cherry Street. Elizabeth wasted no time in recommending Edward, who was not quite 9 years old, for the post. And it was here that he would remain for the next 17 years (Fig. 17.2). Van Stavoren’s solar camera was one of the largest ever constructed and was designed to make life-sized enlargements on silvered paper from the corresponding negatives. Such work required an intense solar beam necessitating the camera to be precisely aimed at the Sun throughout the day. Barnard’s job was to turn a set of wheels at the side of the instrument in order to track the Sun across the sky. There was absolutely no room for error, though, as to do so would have risked setting the studio on fire! And while many lesser mortals fell asleep from pure boredom, Edward would not. Indeed, never once in the long years he operated the camera, nicknamed Jupiter, did he lose his bearings. But even here, Barnard discovered things that many others would never have contemplated, including, according to his biographer, William Sheehan, what astronomers call the equation of time: I knew that the sun attained its greatest altitude at noon. I amused myself by determining when noon had arrived by the fact that then I ceased to raise the instrument to follow the sun. I also established a noon mark by the aid of a shadow of a chimney. But I was surprised soon to find that neither of these signs agreed for any length of time with the noon ringing of the bell in a Catholic Church (St. Mary’s) nearby; sometimes the noon, as indicated by the highest altitude of the sun or by his noon mark, was too soon and at other times too late according to the church bell; the difference sometimes amounting to a considerable fraction of an hour. This set me thinking and wondering, but it was many years afterwards before I found out the explanation of this singular phenomenon, which was due to the equation of time.

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Fig. 17.2  The Jupiter apparatus mounted atop the roof of the Photographic Gallery, Nashville, Tennessee. (Image courtesy of Vanderbilt University, c. 1866)

Putting in long hours at the photographic gallery, Barnard would often make his way home well after sunset. As he walked he would notice the starry heaven above his head, and on one occasion a bright yellow star that did not keep its position relative to the fixed stars of the firmament. Unbeknown to him at the time, Barnard had unwittingly encountered the bright planet Jupiter. By the late 1860s, Van Stavoren’s business began to fail, and by 1871 he was bought out by a one Rodney Poole, who retained Barnard in his employ, though his role would have to change with the fashions of the time. ‘Jupiter’ was dismantled, and Barnard found himself selling outdoor photography kits and sign painting, an activity he was particularly good at. All of a sudden, the young man from Nashville had high ambitions to become an artist of sorts. But to the relief of future astronomers, his bubble was burst when Poole hired Peter Ross Calvert, a properly trained colorist and retoucher, whose practical work greatly surpassed that of Barnard. In the evenings after work and some supper, Barnard would devote himself to study, reading any books that would come his way. But on one auspicious occasion he was introduced to a book, the subject matter of which was astronomy. In his own words Barnard wrote:

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One night while pouring over some old books on mathematics which I had purchased second hand and perhaps not wisely… a young man came to my room…. We had been children together, but he was a born thief. As a boy he stole, and when he got older the law often laid its hands upon him. On several occasions I had helped him out from my meagre earnings, for my sympathies were easily worked upon. At one time I had paid his fine when a policeman brought him around where I was at work. In this night in particular I was in no mood to be gracious, for he came to borrow money from me, which I knew from previous experience would never come back. As security for the return of the money he had brought a large book. This I refused to look at; and finally, to get rid of him, I gave him two dollars (which was the amount asked for). I never saw him or the money again. Shortly after he had gone I noticed he had left the book lying open upon my table. I felt very angry, because the money was a large amount to me then, and it was sometime before I would open the book.

When he did eventually open it, Barnard was amazed at its contents! The opening section presented a series of essays on covetousness, but what really piqued his interest was an additional section dedicated to astronomy, of all subjects! In a treatise written by the Reverend Thomas Dick called, appropriately enough Dick’s Works, he discovered a set of star charts that enabled Barnard to finally name the stars that had befriended him from his youth. Indeed, according to his future friend and astronomical colleague, S. W. Burnham, he studied the book “with great avidity.” What particularly appealed to Barnard was the author’s attempt to reconcile science with the Christian faith. Soon Barnard was sharing his passion for all things astronomical with his work colleagues, and it so happened that another of Poole’s employees, a Scotsman by the name of James W. Braid, also expressed an interest in astronomy. Some 10 years Barnard’s elder, Braid was Poole’s chief photographer and had a good knowledge of basic optics. It was Braid who hobbled together the necessary lenses to make the first telescope Barnard would ever use. Consisting of nothing more than a paper tube into which some lenses were mounted, the instrument was a very crude affair, but Barnard found looking though it an exhilarating experience, using it to explore the battered lunar regolith with its rugged mountains and crater fields, as well as the constantly changing aspects of Jupiter’s bright satellites. As crude as this first optical accoutrement was, it most certainly whetted Barnard’s appetite for a better telescope. And Braid once again came to his rescue, constructing a 2.25-inch achromatic telescope with a focal length of 32 inches. Salvaging an old microscope eyepiece, the telescope gave good and sharp images with an enlargement of about 38 diameters. The telescope was then mated to a disused surveyor’s tripod for mounting. With this improved instrument Barnard enjoyed his first glimpses of the phases of Venus and the Great Nebula in Orion. Indeed, it is he that originated the oft-used description of the same object as a celestial ‘bat.’ “This simple telescope,” Braid later recalled, “gave Barnard more pleasure than anything else in life.” This was the instrument Barnard came of age with, for he had just turned 18. No sooner had he begun using the 2.25-inch that Barnard learned of the existence of yet another, slightly larger telescope in Nashville, which was in the possession of the wealthy Acklen family. But he was not acquainted with these upwardly mobile folk, and was too unassuming to muster the courage to visit their mansion house at

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Belmont. Better to write a polite letter of introduction in which he could make inquiries about the instrument he so desperately coveted. But Barnard had no experience in the art of polite and persuasive letter writing, so he turned to his more genteel colleague, Calvert, for assistance. Calvert agreed to help but only on the proviso that Barnard attend the Baptist Sunday School. Barnard agreed, and the letter of introduction was dispatched. To his great delight, Barnard got a reply where he was informed that he could indeed borrow the telescope on a short trial basis, and if it performed satisfactorily he would pay them the full asking price. Unfortunately, this was an instrument that was better to look at than through, for he found it to be mediocre at best. Still he had to pay the full $9.35 (a sum that represented more than three-quarters of his weekly salary) charge to have it safely delivered back to its owners. Barnard did, however, thoroughly enjoy his visits to Sunday school, a regular habit he maintained all the time he remained in Nashville. By now, Barnard was suitably well versed that he knew it was a good thing to invest in a quality instrument. But his next telescope acquisition, a 3-inch equatorial, also proved mediocre, and soon he sold it for cash. He would have to save hard to get the instrument that would progress the love of his life. As luck would have it, Braid got wind of good 5-inch equatorial refractor made by the noted telescope maker, John Byrne of New York. Byrne was originally apprenticed to Henry Fitz, maker of fine refracting telescopes for the discriminating amateur. The asking price would take Barnard’s breath away though, a whopping $550. Braid, who had connections to the Byrne family, managed to negotiate a reduced sale price of $380. Still, this represented a full two-thirds of Barnard’s annual salary at the Photograph Gallery. Working up the courage to ask Poole for a loan, Barnard got the cash to buy the telescope “with the last cent I had in the world,” he wrote, “besides going heavily into debt to make up the requisite price” (Fig. 17.3). The instrument arrived in Nashville sometime in early 1877, where he would immediately begin to use it to explore the heavens. His first night with his ‘large telescope,’ as Barnard put it, reads like a prayer: The first clear night after receiving my large telescope, I sat out on the roof of a three story house all night long, surrounded by ice and snow, the night being bitterly cold. After exploring the wonders of the moon until it sank from view beneath the western horizon my telescope sought the Milky Way. Here amid the splendor of that mighty zone of stars, I spent hour after hour sweeping among its marvellous fields of glittering suns, never wearying of the wonders constantly presented with each movement of the telescope, but gaining additional enthusiasm as the night drew apace. Nor did I forget the many double stars and clusters I had learned with my smaller instruments for they were each examined and I wondered at the beautiful contrasts of color in some of the binary systems and the myriads of stars revealed in the clusters that I had but dimly seen before with that small telescope. But from these lesser lights my telescope constantly swung back to the Milky Way, again to gaze on the ‘broad and ample road where dust is stars.’ So enraptured was I with these glimpses of the Creator’s works that I heeded not the cold nor the loneliness of the night. And when the approaching dawn began to whiten the eastern skies, I sought out the great planet Jupiter, then only just emerging from the solar rays, and beheld with rapture his four bright moons and vast belt system. But when the dawn had paled each stellar fire the coldness of the night forcibly impressed itself upon me and I retired from the field of glory.

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Fig. 17.3  The author’s 5-inch f/12 classical achromat, an instrument very similar to the Byrne refractor used by the young E. E. Barnard. (Image by the author)

Barnard was justifiably proud of his 5-inch refractor, or his ‘pet,’ as he referred to it in future correspondences. Indeed, his telescope was the largest in all of Nashville, save for the 6-inch Cooke equatorial at nearby Vanderbilt University. The archives show that the earliest recorded observation of a planet made with his 5-inch glass was dated to March 10, 1877, which show some pencil sketches of Uranus when it was a mere 3° from the bright star Regulus. On this evening he caught it with a low power of 52 and followed up those observations with oculars delivering higher magnifications of 101 and 173. It was that same year that Barnard met with Simon Newcomb, a distinguished astronomer from the U. S. Naval Observatory, who was attending a meeting of the American Association for the Advancement of Science (AAAS) being held at the State Capitol in Nashville. Barnard asked Newcomb how he might best advance in the field of astronomy given a small telescope. Newcomb advised him to look for comets and to conduct drawings of the various nebulae. He also mentioned the seminal work of a one S. W. Burnham, whose extraordinary eyes had shown him a suite of new and extremely tight double stars using only a 6-inch Clark refractor. Newcomb then inquired as to whether or not Barnard had studied mathematics to an advanced level. Timidly, he responded in the negative, to which Newcomb is reputed

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to have responded: “Lay aside at once that telescope and master mathematics, for you will never be what you seek to become without this mastery.” According to another account, this last remark deeply upset the young stargazer, for he immediately left Newcomb’s company to hide behind one of the columns of the capitol and burst into tears! Luckily, he didn’t entirely take Newcomb’s advice and soon determined to divide his spare time studying mathematics on cloudy and moonlit nights with the help of a hired tutor (who he had to pay out of his meager earnings) while continuing his telescopic work any time the night sky was clear and dark. As the AAS was in session, the Red Planet came within 35 million miles of Earth, and Barnard eagerly turned his ‘pet’ toward it. Because the mount was rather light weight, Barnard had to keep the magnification down from where it could theoretically go. In general, 173x was the highest he would squeeze out of it, but it was great enough an enlargement for him to make out the main features of the Martian disk. He noted a white cap on the planet and watched it gradually shrink in size. From this he correctly deduced that these were made of ice (actually a mixture of dry ice and water-ice). The ruddy patches, he concluded, were landmasses, and he even watched wispy patches near the limb of the planet that he correctly attributed to cloud formations. Remarkably, though he was scarcely 20 years of age, he refused to entertain the notion that Mars was inhabited by life forms. To Barnard, this was just wild speculation that had no place in a proper assessment of planetary science. Observing the planet again at the opposition of 1879, he seriously entertained the idea of publishing his own short book on Mars, inspired as he was by Richard A. Proctor’s opus, Saturn and his System. The book Barnard had in his mind’s eye, Mars: His Moons and His Heavens, was certainly an ambitious project, for not a single book-length treatise of the planet had yet been published in the English language. Though he did manage to write a booklet of sorts (less than 100 pages in all), it was never published. Perhaps his failure to bring the work to fruition reflected the time he spent courting a fellow employee at the gallery, Rhoda, sister of Peter Calvert, whom he married in 1881. And though she was fully 13 years his elder, the marriage proved a long and happy one, though sadly childless. Through 1879 and 1880, Barnard used his 5-inch Byrne to undertake a detailed study of Jupiter, and in particular, the nuances of its most famous feature, the Great Red Spot. He noted very subtle changes to its form, color and brightness. The drawings he left behind record a great deal of subtle detail, and it is apparent that even by now, he had a well-trained telescopic eye. For example, in his observing book dated to October 23, 1880, he writes: Jupiter is undergoing some remarkable changes now, there are a great many degrees of shade, somewhat like ill shaped spots and light spaces, appearing in the northern hemisphere near the Great Red Spot. The space between the north edge of the north equatorial band and the first linear belt is deepening in tint….[It is now] a grayish green [and] near the following limb is knobbed in appearance, as if several dark beads strung on it.

In those days, the discoverer of an icy comet could win a cash prize as well as considerable fame. In particular, the Warner prize offered $200 for such a discovery, the first recipient of which was fellow American, Lewis Swift, who found his sev-

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enth comet on April 30, 1881. Barnard took to comet hunting like a proverbial duck to water, spending long hours sweeping the skies over Nashville at ungodly hours of the morning. On May 12, 1881, Barnard discovered his first comet, which unfortunately, he did not announce. He found his second comet on September 17 of the same year, and another one on September 13, 1882. A lesser man might have squandered the cash on a larger telescope or some such. Barnard, however, used the money to put a deposit down on a home for his wife and his poor mother, who was, by this time, an invalid. But times were changing, and now, every astronomer in the world knew Barnard’s name, and it wasn’t long afterwards that he was appointed to a professional post at Vanderbilt University, completing his degree in mathematics by age 30. And the rest, as they say, is history.

Sources Barnard, E.E.: Changes in the Length of the Great Red Spot on Jupiter. http://articles.adsabs. harvard.edu/full/1885Obs.....8..244B. Barnard’s Byrne refractor through modern eyes. https:// www.cloudynights.com/topic/480795-testing-an-antique-john-byrnes-objective-at-stellafane/ Sheehan, W.: The Immortal Fire Within: The Life and Work of Edward Emerson Barnard. Cambridge University Press, New York (1995) Sheehan, W.: E. E. Barnard and Mars: The Early Years. http://articles.adsabs.harvard.edu//full/199 3JBAA.103...34S/0000035.000.html?high=527c0bc11b27852

Chapter 18

William F. Denning, a Biographical Sketch

Remember the days of old, consider the years of many generations: ask thy father, and he will shew thee; thy elders, and they will tell thee. – Deuteronomy 32:7 Oh Spring! Dear Spring! Thou more must bring Than birds, or bees, or flowers – The good old times, the holy prime Of Easter’s solemn hours: Prayers offer’d up and anthems sung Beneath the old church towers. – W. F. Denning

The mid to late nineteenth century was a period of frenetic astronomical activity in Britain. Inspired by the enthusiasm of home-grown ‘clerical’ popularizers of astronomy, such as W. R. Dawes and T. W. Webb, a new generation of British amateur astronomers arose, forming societies across the length and breadth of the country. They would take up the gauntlet of observing the heavens in search of booty. Telescopes were becoming more popular, not just the achromatic refractor, which held a special place in the history of Victorian astronomy, but also the Newtonian reflector, which was experiencing a bit of a Renaissance owing to the introduction of silver-on-glass mirrors offering decent aperture at prices that suited the budgets of many more amateurs. It was in this renewed spirit of enthusiasm that William F. Denning was to make his mark on the astronomical community (Fig. 18.1). Little is known of his early life. The eldest son of Lydia and Isaac Denning, William was born on November 25, 1848, in the picturesque village of Redpost, Somerset. Isaac was a retired army officer-turned-accountant, who provided a modest income for his family. When William was seven, the Denning family moved to the city of Bristol, presumably to realize a higher standard of living by entering into an accountancy partnership – Denning, Smith & Co – where they prospered and were further blessed by three more children – a brother Frederick and twin sisters, Margaret and Emma.

© Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_18

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Fig. 18.1  A lovingly refurbished 10-inch Calver reflector. (Image courtesy of Robert Katz. Used with permission)

Not much is known of William’s education, although judging by the standards of his many later astronomical correspondences, it is reasonable to assume that he received a good foundation at school. After leaving formal education, William followed his father into the accountancy business, remaining with the firm until Isaac’s death in 1884. William showed great promise as an athlete and cricketer and even dabbled in hockey. Indeed, according to a later account by T. E. R. Philips, Denning was invited by the legendary cricketer Dr. William G. Grace to be a wicket keeper for the county of Gloucestershire  – a considerable honor in itself  – although for reasons that still remain obscure, he declined the offer. One guess is that the young man had other ambitions related to astronomy, which he had expressed an interest in as early as 1865, aged just 17. One event that may have consolidated his decision to follow an astronomical career was the great Leonid meteor showers that occurred between 1866 and 1868, during which time many spectacular fireballs were witnessed streaming across the mid-November night sky. Denning then opened a correspondence with Alexander S. Herschel, the son of Sir John Herschel, who had carried out pioneering work on

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meteor spectroscopy. And while meteor watching was to become the enduring passion of Denning’s later life, his earliest forays into the hobby were decidedly varied. In 1865, Denning bought his first telescope, a good 4.5-inch refractor, with which he would carry out extensive work on the groupings of sunspots, observations of the transit of Mercury in the year 1868, as well as transit timings of the Galilean satellites of Jupiter, the latter of which formed the basis of his first publication, aged just 20, appearing in the Astronomical Register 6, Vol. 92, 1868, and auguring his subsequent meteoric rise in the community of British amateur astronomers. This first publication in the Astronomical Register was immediately followed up by several others in the next few years, during which time Denning was to spearhead a coordinated effort among dozens of his fellow amateurs to observe the Sun for a month-long period between March 14 and April 14, 1869, in order to search for the elusive planet Vulcan, which was postulated to exist inside the orbit of Mercury. Although no such planet was ever seen, it did not in any way diminish his enthusiasm for coordinating multi-observer surveys in the future. Indeed, it was this boyish enthusiasm for his work that led to him founding a new society with the help of his more influential astronomical friends. Known as the Observational Astronomical Society (OAS), this organization was established on July 1, 1869, with Denning himself acting as its first treasurer and secretary. Although the OAS did not ultimately have the legs to endure the sweeping changes that occurred over the coming years, ceasing to exist altogether after 1872, many would agree that it was a legitimate foreshadowing of the much more successful British Astronomical Association (BAA), which was founded in 1890, and which is still going strong today. Intrigued by the growing interest in large aperture silver-on-glass reflectors that were the talk of the town during these years, and sensing ‘the pomp and ceremony’ of refractor culture, Denning used his brain and took a punt on a 10-inch f/7 With-­ Browning reflector with a simple alt-azimuth mounting, which he purchased in 1871. Being unusually enthusiastic about exploring the telescope’s potential under the starry heavens, the truth soon set him free, and he embraced the same instrument to embark on an extraordinary program of visual work on the bright planets. It was these observations, and his subsequent commentaries, that were to abruptly hurl the young man into the limelight of the international astronomical community. Over the next 15 years or so, Denning became universally acknowledged as one of the finest planetary observers of his age, and especially of Jupiter. Having access to the best astronomical literature of the day, he became acutely aware that the drawings made by astronomers using larger telescopes were not revealing as much detail as one might have anticipated from their superior aperture. As a case in point, he argued that the Jovian whole disk drawings carried out by the third Earl of Rosse using the 72-inch Leviathan of Parsonstown were no more detailed than what was revealed by backyard telescopes with very modest apertures in comparison. In addition, being intimately familiar with the work of other great observers of his era, such as the English solicitor and amateur astronomer Stanley Williams, who had used a 6.5-inch Calver reflector on a simple equatorial mount to make all of his highly

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detailed observations of the Giant Planet, Denning reached this remarkable conclusion in a publication communicated in 1885: Many people would consider that in any crucial tests the smaller instrument would be utterly snuffed out: but such an idea is entirely erroneous. What the minor telescope lacks in point of light it gains in definition. When the seeing is good in a large aperture, it is superlative in a small one. When unusually high powers can be employed on the former, far higher ones proportionally can be used with the latter. We naturally expect that very fine telescopes, upon which so much labor and expense have been lavished, should reveal far more detail than in moderate apertures, but when we come to analyze the results it is obvious such an anticipation is far from being realized. The glare of excessive light and the endless moldings and flaring of the image can only have one effect in obliterating delicate markings.

Denning’s comments were made in response to some criticisms of both his work and the observations made by other keen observers he enjoyed correspondences with, who seemed to confirm rapid atmospheric changes in Jupiter’s massive turbulent atmosphere. In particular, they were directed at the comments made by the professional American astronomer, G.  W. Hough, who employed the 18.5-inch Dearborn refractor near Chicago, in his own Jovian studies, but who had failed to notice the same changes. Consequently, Hough dismissed the reports of Denning et al. as being attributed to “the poor quality of the images” in the smaller telescopes. Rising to Hough’s criticism, Denning not only reaffirmed what he and others had seen but began to seriously wonder why Hough had missed seeing these changes with such a formidable telescope. In another 1885 publication, Denning writes: “Apertures of 6 to 8 inches seem able to compete with the most powerful instruments ever constructed…a very large aperture shows the rushing of vapors across the disc, and violent contortions of the image, which are the inevitable result.” In support of his conclusions, Denning pointed out that the disk drawings of Mars made by Asaph Hall and the Scots-born American astronomer, William Harkness, were noticeably ‘bland’ in comparison with those drawn by the Reverend Dawes and Giovanni Schiaparelli, who both used instruments of 8-inch aperture, as well as the fine work of the British artist, Nathaniel Green, who had conducted extensive Martian observations from the Madeira archipelago, off the coast of Morocco, using a 13-inch silver-on-glass reflector. In addition, Denning also brought Sir William Herschel’s opinions in these matters to the fore: Sir William Herschel seems to have the non-utility of large instruments in the observation of bright planets for he wrote as follows: “On the course of these observations [on the belts of Saturn] I made ten new object specula and fourteen small plain ones for my 7 foot [6.3 inches] having found that with these instruments I had light sufficient to see the belts of Saturn well and that here [Bath, England] the maximum of distinctness might be much easier obtained than where large apertures were concerned.” After Nathaniel Green acquired his ‘ultimate’ telescope back in England – a reflector of 18 inches aperture – he found it useful to fit it with a “convenient gradation of stops.”

This was just the ammunition Denning needed to drive home his own findings: If a large diameter telescope is useless without stops, wherein does its utility consist? Better at once to adopt a smaller speculum and obviate the more troublesome manipulation of a

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large instrument. True there are very rare occasions when all the aperture may be utilized; but are they worth waiting for, and when they come, do the results answer expectations?

Denning undoubtedly had a point, as the air cells coursing over the British Isles do indeed seem to favor moderate but not large apertures, but it was not true everywhere. For example, in a study conducted by the American astronomer, Charles A. Young, using the 23-inch Clark refractor at Princeton, New Jersey, he admitted that while small apertures are less sensitive to the vagaries of Earth’s atmosphere, in his opinion, the images through the 23-inch were generally far superior to those garnered by the 9-inch glass with a frequency of about one night in three. Notwithstanding these comments, Denning was no Luddite, acknowledging that for other avenues of astronomical observing, aperture was an indispensable commodity: “In certain departments of research large apertures are absolutely required, and have performed work utterly beyond the capacity of moderate instruments.” Denning’s keenness for observing was legendary, so much so that it is no wonder he did so well with such a modest telescope without a driven mount, and no cooling fans – a circumstance that flies in the face of the modern amateur, who often regard such devices as ‘essential.’ Denning’s reports are also entirely in keeping with the author’s own field experience with a modern 8-inch f/6 Newtonian, which has proven to be among his best and most used telescope (also un-driven and with no cooling fans). We may gain a glimpse of Denning’s extensive experience by taking a look at a few comments he made in Chapter VIII of Hutchinson’s Splendour of the Heavens: “The telescope’s definition of Jupiter varies greatly according to the altitude of the planet. From 487 nights of observation (10-inch reflector) at Bristol the following percentages were observed: % Nights Jupiter South of Equator Jupiter North of Equator

Very Good 7.0 19.8

Good 14.1 29.1

Fair 15.5 25.6

Bad 33.8 18.6

Very Bad 29.6 7.0”

The reader will note the great advantage of observing the planet higher in the sky as viewed north of the celestial equator, where the orb is less affected by atmospheric turbulence. Note also the percentage of useful nights and/or observing spells Denning enjoyed from Bristol; a number wholly inconsistent with the ‘perpetual bad weather myth’ promulgated by modern amateurs. Self-evidently, there were more clear nights where work could be done over ‘cloudy’ England than is commonly reported today. Intriguingly, this anomalously high frequency of good observing nights/spells communicated by Denning was also independently reported by the consummate British amateur, Charles Grover (discussed later in this book), who’s biographer revealed that he observed on 146 nights (40%) during the year 1886. Denning was a keen observer of Jupiter’s Great Red Spot (GRS), watching it change in color, shape and size over many years with his With-Browning reflector, and about which he discusses at great length in Splendour of the Heavens. On the

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evening of February 13, 1888, Denning made a sketch of the Giant Planet with his 10-inch alt-azimuth reflector, which shows a considerable amount of detail. The size of the GRS is relatively enormous, though, much larger in comparison to anything seen in recent years. The reader will note a large, bright, cloud-like structure encapsulated within the spot. Another Jupiter drawing, by the young E. E. Barnard, using a fine 5-inch f/15 Byrne refractor, was made very close in time to Denning’s sketch, though several years’ later. As one set of plates dated April 22, 1886, show, Barnard’s superb eyesight recorded an equally large GRS with the same cloud-like structure inside it, and with an accompanying note (seen on the previous page), which states: “A white cloud has formed over the middle of the Great Red Spot, almost obliterating it.” Could Denning and Barnard have observed the same feature, albeit a couple of years apart? It’s very probable! Comparing the detail of the two sketches, we also see the superior resolving power and contrast transfer of Denning’s reflector coming into play. Denning’s contribution to planetary astronomy extended well beyond Jupiter, though. For example, in 1876, Professor Asaph Hall, using the great 26-inch refractor at the U. S. Naval Observatory, recorded an equatorial spot on Saturn, which he followed and measured through 60 rotations, and from these data deduced its period to be 10 h, 14 min and 24 s. Hall was careful to stress that this may not have been the rotation period of the planet per se, only that of the spot itself. Back in England, both Denning and Stanley Williams, using far more modest 10-inch and 6.5-inch Newtonian telescopes, respectively, were following vague markings on the Saturnian globe and came to a rotation period just 2 s shy of Hall’s estimate, all of which are in agreement with the best modern values for the planet’s rotation.

An Aside: Quality Never Goes Out of Fashion! How good were With and/or Calver mirrors? In a word, excellent, by all accounts. Calver deliberately left his mirrors slightly undercorrected to compensate for the natural overcorrection a mirror would exhibit as it cooled off. Robert Katz, a London astronomer, who lovingly restored a magnificent 10-inch f/8 Calver reflector on a simple alt-azimuth mount, shared his experiences of the telescope: My f8 10" Calver looks like an unwieldy beast and by any modern standards is overwhelmingly long. The original wooden stand had rotted and was missing its slow motion controls when I found it, but luckily Len Clucas, the former professional telescope-maker for Grubb Parsons in Newcastle had inherited an identical stand and cradle from the late master mirror maker David Sinden which he refurbished for me. A stepladder is essential for objects over 30 degrees high and viewing near the zenith is positively dangerous. And yet – climbing up to the eyepiece apart  – it is remarkably easy to use. The eyepiece is always in a convenient position – assuming you can reach it – the azimuth and altitude controls are smooth and make tracking easy even at powers of 300x and the ingenious system of a clamped tangent arm makes rewinding the azimuth screw simple without losing position. Even though it weighs a ton the telescope is also beautifully balanced; unclamped from the

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slow motions, with a 40-mm eyepiece in the barrel, I imagine it is the closest you can get to the laid-back star-hopping Dobsonian experience with Victorian equipment. The optics are fine and because the focal length is actually less than that of a standard SCT, views of deep sky objects are impressive with a low power eyepiece. It comes into its own with the planets, though, and the exceptional opposition night of Jupiter in September 2010 was memorable in many ways. Thanks to good seeing in South West London – the telescope is in Hampton Hill – I spent most of the night watching Jupiter turn in exquisite detail using a fine telescope made in 1882 by one of the two great telescope makers of his day; but a telescope so simple that a child can learn to operate it confidently in five minutes.

Thus, by all accounts, these fine Newtonian telescopes were first-rate tools that enabled their owners to conduct detailed studies of the firmament. The fact that Denning and others used an alt-azimuth mounting to conduct planetary studies (most of which were published in the best astronomical journals of the day) is also to be noted. Today, there is a tendency among some amateurs to dismiss the use of an undriven alt-azimuth mount because it doesn’t keep the planet in the center of the field. Truth be told, though, there will be plenty of opportunities when the finest details of a planet’s aspect can be made out as it crosses the field of view. So, like everything else in life, intrepid folk always find a way around such technical obstacles. In parallel to his growing interest in planetary observing, Denning took up the activity of comet hunting sometime in the 1870s, and he was rewarded for his efforts in the predawn hours of October 4, 1881, when, shortly after a spell observing Jupiter, he inserted a low power eyepiece and began sweeping the sky in its vicinity. Almost immediately he caught sight of a ‘suspicious’ object that turned out to be a new short-period comet. Nearly another decade elapsed before discovering his next icy interloper, which he stumbled upon in 1891, and this was followed by two other comet discoveries in 1892 and 1894. For each of these discoveries, Denning was awarded the bronze medal by the Astronomical Society of the Pacific. Denning was also the co-discoverer of a comet with the famous American astronomer, E.  E. Barnard in 1891. His publication rate rising to some 20 articles per year, Denning’s reputation as an observer of repute grew steadily, so much so that he was elected president of Liverpool Astronomical Society for the year 1887, increasing its already large membership from 440 to 641. In addition to his published articles, Denning embarked upon writing books on amateur astronomy. Although his earliest forays into this brave new world was met with unnecessarily harsh criticisms from the priggish founding editor of the scientific journal Nature, Sir Norman Lockyer, his later books, including Telescopic Work for Starlight Evenings (1891), were enthusiastically endorsed by the powers that be. We shall dedicate an entire chapter to this work to extract the accumulated knowledge of Victorian amateur astronomy. Many more accolades were bestowed upon W. F. Denning in the closing decade of the nineteenth century, not only at home but abroad. The Valz Prize of 1895 was awarded to him by the French Academie des Science, and in 1898 Denning received the prestigious Gold Medal of the Royal Astronomical Society in recognition of his

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monumental work on meteors. He was even given a mention in Chap. 2 of H. G. Wells’ famous novel The War of the Worlds, which was first serialized in 1897. Although it is undoubtedly true that Denning expressed an interest in the Martian canal theory, he was not convinced of the existence of canals, stating that” they were far more highly suggestive of natural than artificial production.” It is not known exactly when Denning acquired his largest telescope, a 12.5-inch Calver reflector, but what is certain is that he never acquired equatorial mounts for any of them. Nor did he bother building an observatory for his telescopes, a custom quite out of sync with the prevailing culture of his day. His writings were simplistic and unassuming, but they also reveal the workings of a true telescopic draughtsman, where accuracy and objective truth were held in higher esteem than artistic license. By the end of the nineteenth century, W. F. Denning was one of the most famous astronomers in the world, commanding an extraordinary web of correspondence with the scientific giants of his age. And while the accolades kept piling up, Denning’s reaction to this new-found fame was not in keeping with a man of his standing. An admixture of declining health and bitter criticism over his ideas regarding the stationary nature of meteor radiants, conspired to alienate the consummate English amateur so much so that he eschewed the limelight and became increasingly reclusive, giving up telescopic astronomy altogether by 1906. It is not known how Denning made a living in the last few decades of his life, but it is true that he did receive a Civil List Pension by the British government beginning in 1904, when he was 56  years old. This amounted to an annual stipend of £150, “in consideration of his services to the Science of Astronomy, whereby his health has become seriously impaired and of his straitened circumstances.” And while there is no evidence that he earned an income from the family accountancy business, it has been suggested that he received sporadic payments for his literary works, and some occasional prize money for his discoveries that just barely kept the wolf away from the door. Though he lived a solitary life, Denning kept up communication with the outside world through his many letters of correspondence and scientific publications. And while his telescopic career was now far behind him, it was by no means the end of his discovery days. In a singular period between 1918 and 1920, Denning, now a septuagenarian, observed a nova in Aquila (V603 Aql), the discovery of which was later contested. However, during a routine meteor watch in August 1920, the 72-year-old Denning discovered a new star in Cygnus, shining with a magnitude of 3.5. Nova Cygni was the talk of the astronomical world for many months to come, and he enjoyed a surge in correspondences from an adoring international following. As well as his correspondences, Denning took to writing poetry, in which he often explored the themes of nature, her cycles of decline and renewal. It has been suggested that Denning cultivated a strong Christian faith. The last decade of Denning’s life is one of great sadness. Upon visiting him at his last known address at Eggerton Road, Bristol, in 1922, Dr. W.  H. Steavenson recalled meeting a wretched soul, living in abject poverty, and with only an open fire and a tobacco pipe as sources of comfort. Even when Denning

Sources

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left the house, he became the butt of every schoolboy’s joke, who ignorantly taunted the eccentric astronomer. Denning remained an active observer of the heavens right up until a few weeks before his death on June 9, 1931, at age 83, caused by heart disease. Entirely self-­ taught, and arguably the most active and gifted observer of his generation, he will be remembered for his unbridled enthusiasm for his science, his love of nature and for his encouragement of a new generation of stargazers across the world.

Sources Beech, M.: W.  F. Denning  – The Doyen of Amateur Astronomers. http://hyperion2.cc.uregina. ca/~astro/DEN/short_bio.pdf Beech, M.: Denning on Novae. http://uregina.ca/~astro/DEN/nova.pdf Clerk, A.: A Popular History of Astronomy During the Nineteenth Century. Cornell University Press, New York (2009) Denning, W.F.: Telescopic Work for Starlight Evenings, Cornell University Library, New York (2010) Denning, W.F.: The Defining Powers of Telescopes. http://articles.adsabs.harvard.edu//full/1885O bs.....8..205D/0000205.000.html Denning, W.F.: Jupiter and the Relative Powers of Telescopes in Defining Planetary Markings. http://adsabs.harvard.edu/full/1885Obs.....8...76D Denning, W.F.: Obituary. http://adsabs.harvard.edu/full/1931Obs....54..276 E.  E. Barnard’s drawings of Jupiter dated 1880 to 1886 and carried out with his 5-inch Byrne refractor. https://archive.org/stream/jstor-40666891/40666891#page/n23/mode/2up Obituary Notices: Fellows:- Williams, Arthur Stanley. http://articles.adsabs.harvard.edu//full/1939 MNRAS.99R.313./0000313.000.html Philips, T.E.R. (ed.): Hutchinson’s Splendour of the Heavens, vol. 1. Hutchinson & Co, London (1923)

Chapter 19

A Modern Commentary on W. F. Denning’s Telescopic Work for Starlight Evenings (1891)

An Essay Dedicated to David Gray. Humility is the fear of the Lord; its wages are riches and honor and life. – Proverbs: 22:4

William Frederick Denning (1848–1931) is not a name that trips off the tongue of the modern amateur astronomer. Of all the sky watchers of that era, it is arguably the literary work of the Reverend Thomas William Webb, and especially his Celestial Objects for Common Telescopes, that is most celebrated by amateur astronomers. But while a great work in its own right, Webb was by no means the only popularizer of astronomy in England, nor was he necessarily the most knowledgeable and dedicated to his hobby. That accolade, in the opinion of many, should be reserved for an obscure Bristolian, who emerged from relative obscurity in what was the meritocracy of the Victorian astronomical tradition, to pen one of the loveliest treatises on the art of visual observation, both with and without a telescope (Fig. 19.1). In this essay, we shall explore Denning’s masterful tome, Telescopic Work for Starlight Evenings. First published in 1891, it was intended to bring to the modern reader a distillation of late nineteenth century astronomical knowledge, presented in such a way as to captivate the widest possible audience, both young and old, rich and poor, novice and learned alike. As explained in the preface to the work, the book was conceived of at the behest of some of his closest friends, to gather together the best nuggets from his published writings in The Journal of the Liverpool Astronomical Society (of which he served as president in the years 1887–88), The English Mechanic, and The Observatory, among many others. In Denning’s own words: The methods explained are approximate, and technical points have been avoided with the view to engage the interest of beginners who may find it the stepping stone to more advanced works and to more precise methods. The object will be realised if observers derive any encouragement from its descriptions or value from its references, and the author sincerely hopes that not a few of his readers will experience the same degree of pleasure in observation as he has done for many years.

© Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_19

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Fig. 19.1  W. F. Denning’s Superlative book, Telescopic Work for Starlight Evenings (1891). (Image by the author)

No matter how humble the observer, or how paltry the telescope, astronomy is capable of furnishing an endless store of delight to its adherents. Its influences are elevating and any of its features possess the charms of novelty as well as mystery. Whoever contemplates the heavens with the right spirit reaps both pleasure and profit and many amateurs find a welcome relaxation to the cares of business in the companionship of their telescopes on “starlight evenings”. pp. iv–v

Chapter I: The Telescope, Its Invention and the Development of Its Powers Covering Pages 1–19 In this chapter, Denning sets forth his extensive knowledge of the history of the telescope and its development over time. With an engaging writing style, he offers the reader an excellent summary of the key inventions that led to the state of affairs at the end of the nineteenth century. Burning glasses, carved into a convex shape, were known to the ancients and were used as magnifying glasses. One such example, Denning informs us, was recovered from the excavations of the ancient Roman town of Pompeii, which met its terrible demise in a. d. 79 in the

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aftermath of the eruption of Mount Vesuvius. The Roman writer and philosopher Pliny the Elder (a. d. 23–79) also gave mention to globules of glass, which could focus sunlight so intensely that it could ignite combustible material. The development of spectacle lenses from the thirteenth century onwards is also mentioned, but despite having some grasp of the optical science underlying their prescription, Denning is somewhat perplexed as to why it took so long for their adoption into telescopic devices. That said, he does proffer some tantalizing historical tidbits that the principle might have been known as early as the fourth decade of the sixteenth century: Francastor (most probably a one Girolamo Fracastoro), in a work published at Venice in 1538 states:– If we look though two eye lenses, placed the one upon the other, everything will appear larger and nearer. p. 4

Denning wryly comments that despite attempts by some fame-hungry individuals to claimed the invention of the telescope as their own – in particular Galileo Galilei and Simon Marius – or who pronounced they had ‘figured the principle out’ from a basic axiom of physics, it was very likely the case that one of humankind’s most revolutionary devices was very probably elucidated through purely accidental means! Indeed, Denning entertains the notion that the children of the Middleburg spectacle maker, Zachariah Jansen, might have stumbled upon the telescope by placing two spectacle lenses along the line of sight of their eyes, and unwittingly hit on an ingenious way of seeing faraway objects as though they were much closer. Having said this, Denning appears to align himself with the opinions of many contemporary scholars in attributing the invention of the telescope to a certain Hans Lippersheim (also known as Hans Lapprey), who was in possession of a simple telescope in 1608. On pp. 5–6 he refers to a critical piece of research carried out by the professional astronomer Dr. Doberck, who showed that Lippersheim had applied for a 30-year patent from the Dutch States, in exchange for an annual stipend: He solicited the States, as early as the 2nd of October 1608, for a patent for thirty years, or an annual pension for life, for the instrument he had invented, promising then only to construct such instruments for the Government. After inviting the inventor to improve the instrument and alter it so that they could look through it with both eyes at the same time, the States determined on the 4th October, that from every province one deputy should be elected to try the apparatus and make terms with him concerning the price. The committee declared on the 6th October that the invention useful for the country, and they offered the inventor 900 florins for the instrument. He had at first asked 3000 florins for three instruments of rock crystal. He was then ordered to deliver the instrument within a certain time, and the patent was promised him on the condition that he kept the invention secret. Lapprey delivered the instrument in due time. He had arranged it for both eyes, and it was found satisfactory; but they forced him, against the agreement, to deliver two other telescopes for the same money, and refused the patent because it was evident that already several others had learned about the invention. pp. 5–6

Denning proceeds from here to give an excellent overview of the unwieldy non-­ achromatic telescopes devised by Huygens, Hevelius, Cassini and Campani, among others, who ground and mounted lenses up to 8 inches in diameter with enormous focal lengths (up to 212 feet!) yet all still delivering powers of 150 diameters or less.

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From here, Denning discusses the development of the much more convenient reflecting telescopes – the Gregorian, Cassegrain, Newtonian and other compound designs  – and the problems associated with the construction of metallic mirrors fashioned from speculum metal that tarnished quickly and were exceedingly heavy in the larger apertures. Mr. Denning also discusses the origin of the Herschelian reflector, which involved tilting the primary mirror so that it reached a focus at the side of the tube without the requirement for a secondary flat mirror. The design, so he informs us, dates to 1728, when Le Maire first presented it to the French Academie des Sciences. Herschel adopted the design in order to increase the telescopes space penetrating power (light grasp), since it avoided a second reflection and hence saved more light that would otherwise have been lost with the addition of a second mirror. But such a design could not deliver the ‘defining power’ (image quality) of a conventional Newtonian. This is the principal reason why Herschel’s major work on the study of the planets and double stars were conducted with smaller Newtonian reflectors, which were much easier to operate and afforded the greatest degree of ‘mileage’ under the starry heaven. Denning chronicles the growth in telescopic aperture throughout the nineteenth century, discussing such telescopes as the 6-foot aperture speculum metal mirror built by the third Earl of Rosse as well as those used by Lassell and the great Melbourne telescope, which housed a 4-foot diameter (48-inch) speculum metal mirror with a focus of 28 feet. The latter telescope (produced by Howard Grubb of Dublin) was found to have poor defining power, but Denning seems to lay the blame squarely on the shoddy mechanical setup of the instrument rather than the optician. The chapter ends with a discussion of the invention in 1729 of the achromatic doublet by Chester Moor Hall and John Dollond and its development by Joseph von Fraunhofer, culminating in the creation of the sensational Dorpat refractor of 9.4-­ inch aperture, and its state-of-the-art German equatorial mount, which ushered in the age of astrophysics. Throughout the nineteenth century, astronomers began to build larger and larger refractors, first in Europe and then in North America, housed in magnificent domes that opened on every clear night to advance our knowledge of the heavens, and culminating with the Great Lick refractor of 36-inch aperture atop Mt. Wilson, California, which saw first light just three short years before the publication of Denning’s book. And while the author was aware that still larger refractors would surely come into existence, he seemed more interested in a new technological advance in the production of parabolic mirrors for Newtonian telescopes; enter the silver-on-glass reflector. Beginning on p. 14 and continuing on p. 15, Denning describes the exciting work of the French physicist Jean Bernard Léon Foucault (1819–1868), who published a valuable memoir in which he described an ingenious new method of parabolizing a glass disk followed by the deposition of a thin layer of silver upon its surface, and which exhibited much higher reflectivity than the old copper and tin alloy. It marked the end of the employment of speculum metal in telescope mirrors and ushered in a new age that promised to revolutionize both amateur and professional astronomy.

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What is more, Denning informs us that Foucault developed lab-based methods of testing the accuracy of the parabolic surface in such a way as to render traditional testing methods – which involved time consuming and labor-intensive trials under the stars – unnecessary. The customer could be assured of the quality of the mirror without it ever having been tested under the canopy of night. He writes: Silver on glass mirrors immediately came into great request. The latter undoubtedly possess a great superiority over metal, especially as regards light gathering power, the relative capacity according to Sir John Herschel being as .824 to .436. Glass mirrors have also the advantage in being less heavy than those of metal. It is true that silver film is not very durable, but it can be renewed at any time with little trouble or expense. p. 15

Mr. Denning gives high praise to two British silver-on-glass mirror makers, George Henry With (1827–1904) of Hereford and George Calver (1834–1927) of Chelmsford, whose reflecting telescopes, “were found nearly comparable to refractors of the same size.” p. 15. Author’s note:  Modern scholarship seems to have converged on the name “Lippershey” as one of the earliest constructors of the telescope. Denning refers to the same man as “Lipperheim.” It is amusing that Denning referred to Galileo as “Galilei,” to conform to the use of the surname in reference to individuals. Evidently, he thought it odd, which it most certainly is, in retrospect. Some memes are hard to shake. He also points out that the great American refractors had recently employed powers of 3300 diameters in the resolution of the tightest double stars. Denning, of course, was also a convert to reflectors, after enjoying a fine 4.5-­achromatic (probably of f/15 relative aperture) for a few years with which he carried out extensive solar work – a job ideally suited to the smaller refractor. In the end, though, he sold that telescope in order to purchase a 10-inch With-Browning reflector in 1871 (when he was 23 years old) pictured on page 77 of the book. This telescope, so Denning will inform us, proved far more powerful than his former instrument. Indeed, Telescopic Work for Starlight Evenings is a distillation of 20 years of observations conducted with this same telescope.

Chapter II: Relative Merits of Large and Small Telescopes Covering Pages 20–37 Were it not for the vast sea of air that hugs our planet’s crust, the principles of telescopic astronomy would be clear and unequivocal; aperture rules, period. This is the reason for the spectacular success of the Hubble Space Telescope (HST), which, owing to its 2.4-m primary mirror, has sent back the sharpest images of the heavens ever taken. It is also the reason why the widely anticipated replacement for HST, the James Webb Space Telescope, with its 6.4-m segmented beryllium mirror, is expected to completely outclass it.

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Down here on terra firma, the situation is rather more complicated. Although there is no substitute for aperture if one wishes to pursue faint fuzzies, there is a great deal of anecdotal evidence that there exist practical limits on aperture in the pursuit of the finest lunar and planetary images. In a nutshell, although larger apertures offer the potential to see finer details, the atmosphere through which the amateur observes, often limits or even negates those advantages. Denning was arguably the first astronomer to raise awareness about this important topic, and it was based upon his exceptional experience with instruments of all sizes, as well as his voluminous correspondences with the most active astronomers around the world. Denning begins the chapter by discussing the rise in the number of large observatory-­class instruments that had come to the fore during his lifetime and in past generations. Yet all the while he says, “There are some who doubt that such enormous instruments are really necessary, and question whether the results obtained with them are sufficient return for the great expense in their erection.” p. 20. After discussing the realities of large telescopes, including their housing in an observatory, their mounting and maintenance, Denning extols the virtues of smaller instruments and alludes to a quality this author has previously referred to in the past as ‘mileage’: …..[S]mall instruments involve little outlay, they are very portable, and require little space. They may be employed in or out of doors, according to the inclination and convenience of the observer. They are controlled with the greatest ease, and seldom get out of adjustment. They are less susceptible to atmospheric influences than larger instruments, and hence may be used more frequently with success and at places by no means favourably situated in this respect. Finally, their defining powers are of such excellent character as to compensate in a measure for feeble illumination. pp. 20–21

Denning begins with the telescopes of Sir William Herschel. Concerning his 4-foot reflector erected at Slough in 1789, he states that although Herschel discovered two of the inner satellites of Saturn shortly after the instrument was constructed, little else was achieved with it. Denning claims that Herschel much preferred the convenience of a smaller instrument – an 18.5-inch speculum of 20-foot focus – in performing his famous sweeps for nebulae. Indeed the 4-foot telescope quickly fell into comparative disuse, and his son, Sir John Herschel, after photographing it, had it sealed up for good on New Year’s Day, 1840. For defining power, Denning asserts that the great astronomer allegedly preferred instruments of much smaller size: “He found that his small specula of 7-foot focus and 6.3-inch aperture had “light sufficient to see the belts of Saturn completely well, and that here the maximum of distinctness might be much easier obtained than where large apertures are concerned.” p. 21. Following on from this, Denning discusses the great 6-foot aperture telescope erected by the third Earl of Rosse in Parsonstown (now Birr, Co. Offaly), Ireland. By 1891, this telescope had already been in service for 46  years and thus might provide insights into its relative utility. Denning concedes that it had done important work on elucidating the spiral morphology of many nebulae, M51 being perhaps the finest example. What follows is a fascinating overview of how it behaved. The satellites of Mars had eluded its grasp for three decades, until finally, in 1877, the outer moon, Deimos, was glimpsed twice; yet even then there was so much glare from the

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planet that no accurate measurements of its orbit were forthcoming. With Jupiter, too, its enormous aperture was apparently of little advantage. This seems to be confirmed by a series of drawings made by William Parson’s son, Laurence (1840– 1908), in the year 1873, and reproduced on p.  128 of Thomas Hockey’s book, Galileo’s Planet: Observing Jupiter Before Photography. They reveal no more detail than could be obtained in a telescope ten times smaller. Further insight into the efficacy of the Leviathan is gleaned from comments made by the Irish physicist, G. J. Stoney (1826–1911), who regularly used the instrument and who described his impression of γ2 Andromedae in a note from 1878: The usual appearance [of γ2 Andromedae] with the best mirrors was a single bright mass of blue light some seconds in diameter and boiling violently. On the best nights however, the disturbance of the air would seem now and then suddenly to cease for perhaps half a second, and the star would then instantly become two very minute round specks of white light, with an interval between which, from recollection, I would estimate as equal to the diameter of either of them or perhaps slightly less. The instrument would have furnished this appearance uninterruptedly if the state of the air had permitted. p. 23

Self-evidently, it was not the optical quality of the mirror that was at issue but the environment in which it was placed. This was corroborated by a later observer in charge of the Leviathan, a one Dr. Boeddicker, active during the 1880s, who claimed that on a first-class night, the amount of lunar detail seen with the giant mirror was “simply astounding.” We also learn that powers no higher than 600 diameters could be pressed into service, with occasional references to higher powers (1000x). Denning then considers the work of William Lassell, who fashioned a number of large specula with which he discovered the two large satellites of Uranus, Umbriel and Ariel, independently co-discovered Hyperion, a faint satellite of Saturn and, just 17 days after the discovery of Neptune, its brightest moon, Triton. (This name was not referred to by Denning, as it was not formerly bestowed upon it until 1949, when a second Neptunian satellite, Nereid, was discovered.) Though Lassell, together with his assistant, Albert Marth, discovered a large number of nebulae from the Sun-drenched Mediterranean island of Malta with his largest telescope of 4-foot aperture, Denning points out that it was with his 2-foot instrument that Mr. Lassell made all his planetary discoveries. Indeed, in 1871, Lassell wrote: There are formidable, and, I fear, insurmountable difficulties attending the construction of telescopes of large size…. These are primarily the errors and disturbances of the atmosphere and the flexure of the object-glasses or specula. The visible errors of the aperture are, I believe, generally in proportion to the aperture of the telescope…. Up to the size [referring to an 8-inch O-G] in question, seasons of tranquil sky may be found where its errors are scarcely appreciable; but when they go much beyond this limit (say to 2 feet and upwards), both these difficulties become truly formidable. p. 24

That being said, Lassell also concluded that when conditions were fine, the advantages of aperture were clear for all to see. Concerning his largest telescopes Lassell declared: “Nothwithstanding these disadvantages, they will, on some heavenly objects, reveal more than any small ones can.” p. 24. The chapter continues with Denning providing still more anecdotal evidence for the relative merits of large and small telescopes. Next in line, we hear about the

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24.8-inch Cooke refractor erected by a well-to-do gentleman at Gateshead, England, which, despite its intimidating size, proved to have a “singularly barren record”: The owner of this fine and costly instrument wrote the author in 1885: “Atmosphere has an immense deal to do with definition. I have only had one fine night since 1870! I saw then what I have never seen since.” p. 24

Author’s note:  The Gateshead debacle is a particularly poignant story that has value for contemporary amateurs. Showmanship has no place in astronomy! The chap who installed the telescope obviously gave paltry attention to the environment in which the instrument was erected. The same gentleman seems to have had only a casual interest in astronomy, with little or no real experience of how such instruments would likely perform. The local seeing rendered the great telescope stillborn. One cannot help but wonder how many amateurs have done likewise over the years. Before spending lavish amounts of capital on a telescope, field testing the site on which it is to be constructed or used is mandatory. This accounts for the relative success of the large American refractors atop Mount Hamilton, for example, and the Great Meudon refractor outside Paris (discussed in a later chapter), the sites of which were thoroughly field tested prior to their erection. The chapter continues with Denning relating other reports carried out by astronomers located at various observatories throughout the world. For example, at the Paris Observatory, Dr. M. Wolf gained intimate acquaintance with various instruments, including a 47.2-inch silver-on-glass reflector, and a variety of smaller instruments, including a refractor of 15-inch aperture and 15.7-inch silver-on-glass reflector. Wolf wrote Denning concerning his visual experiences with these instruments: “I have observed a great deal with the two instruments (both reflectors) of 15.7 and 47.2 inches. I have rarely found any advantage in using the larger one when the object was sufficiently luminous.” M. Wolf also avers that a refractor of 15 inches and a reflector of 15.7 inches will show everything in the heavens that can be discovered by instruments of very large aperture. He always found a telescope of 15.7-inch aperture to surpass one of 7.9 inches, but expresses himself confidently that beyond about 15 inches increased aperture is no gain. p. 26

Denning then relates the findings of Professor Young, who was assigned to a number of refractors, the largest being of 23-inch aperture, at Princeton, who related the following: The greater susceptibility of large instruments to atmospheric disturbances is most sadly true; and yet, on the whole, I find also true what Mr. Clark told me would be the case on first mounting our 23-inch instrument, that I can almost always see with the 23-inch everything I see with the 91/2 inch under the same atmospheric conditions, and see it better – if the seeing is bad, only a little better, if good immensely better.” p. 27

Another notable report comes from Mr. Keeler, who gained extensive experience with a number of instruments of various aperture atop Mount Hamilton: Mr. Keeler adds: “According to my experience, there is a direct gain in power with increase in aperture. The 12-inch equatoreal brings to view objects entirely beyond the reach of the 6 1/2 inch telescope, and details almost beyond the perception with the 12-inch are visible at a glance with the 36-inch equatoreal.” p. 28

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Author’s note:  These testimonies help to establish the veracity of a certain notion that, from a visual perspective at least, greater aperture is only advantageous when atmospheric conditions cooperate. The relative efficacy of a given instrument is strongly dependent on the environment in which it is housed. Thus, no contradictions are found between theory and experiment. This author is mindful that this discussion focuses primarily on instruments generally larger than those found in amateur hands, but in recent years there has been an attempt by some amateurs (salesmen?), zealous to promote premium refractors over other models, to cultivate the erroneous view that the former can punch through the seeing better on account of their supposed higher optical quality. This arose from a deliberate twisting of some theoretical work conducted by this author in conjunction with theorist Vladimir Sacek (which dealt mostly with the defocus aberration and its effects in long and short focal length systems). Although it was conceded that a slight advantage may be conferred on such higher quality instruments, in general, the seeing error completely overwhelms any small gains conferred in this way. As a further note of proof, many modern reflecting telescopes have Strehl ratios at or above those exhibited by ED refractors (as measured by their polychromatic Strehl ratios) and so, by implication, ought to punch through the seeing even more effectively. That this is not commonly reported (either historically or in the ‘legitimate’ contemporary literature) demonstrates that the effect is largely fictitious and irrelevant to any serious discussion of this interesting topic. We shall not dwell further on the ideas conveyed by Denning in this engaging chapter, save to say that he concluded that there must exist some optimized aperture combining the best of both worlds for work on average nights: There is undoubtedly a certain aperture that combines in itself sufficient light-gathering power with excellent definition. It takes a position midway between great illuminating power and sharp definition on the other. Such an aperture must form the best working instrument in an average situation upon ordinary nights and ordinary objects. M. Wolf fixes this aperture at about 15 inches, and he is probably near the truth. p. 35

Author’s note:  This author is in agreement with Denning’s general conclusion. Indeed, this topic was explored in relation to the efficacy of resolving double stars, where an 8-inch aperture was found to be optimal in one interesting analysis.

Chapter III: Notes on Telescopes and Their Accessories Covering Pages 38–65 In this chapter, the Last Master discusses the best choices of telescope and accessories needed by the amateur who wishes to pursue a serious, long-term study of the firmament. It begins with some sage advice: The subject of the choice of telescope has exercised every astronomer more or less, and the question as to the best form of instrument is one which has occasioned endless controversy. The decision is an important one to amateurs, who at the outset of their observing careers require the most efficient instruments obtainable at reasonable cost. It is useless applying

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to scientific friends who, influenced by different tastes, will give an amount of contradictory advice that will be very perplexing. Some invariably recommend a small refractor and unjustly disparage reflectors, as not only unfitted for very delicate work, but as constantly needing re-adjustment and re-silvering.* *My 10-inch reflector by With-Browning was persistently used for four years without being resilvered or once getting out of adjustment. Others will advise a moderate-sized reflector as affording wonderfully fine views of the Moon and planets. The question of cost is greatly in favour of the latter construction, and, all things considered, it may claim an unquestionable advantage. A man who has decided to spend a small sum for the purpose not merely of gratifying his curiosity but of doing really serviceable work, must adopt the reflector, because refractors of, say, 5 inches and upwards are far too costly, and become enormously expensive as the diameter increases. This is not the case with reflectors; which come within the reach of all, and may indeed be constructed by the observer himself with a little patience and ingenuity. pp. 38–39

Denning emphasizes the convenience of reflectors over equivalent aperture refractors and mentions the innovations of the new silver-on-glass telescope makers, who managed to decrease the focal ratio, allowing decent aperture and viewing comfort to be maximized. George Calver had already begun to make telescopes with focal ratios as short as 5 or 6, which were now ubiquitous and deservedly popular. Denning estimates that an 8-inch silver-on-glass reflector is equivalent to a 7-inch refractor (referring to a long focus achromatic instrument) in relative light-­gathering power, but in terms of defining power, especially in relation to planetary observing, Denning considers them equally good at equal aperture. Having observed through some of the finest telescopes in England, Denning was in a unique position to offer sensible advice to his readers: An amateur who really wants a competent instrument, and has to consider cost, will do well to purchase a Newtonian reflector. A 4 1/2-inch refractor will cost about as much as a 10-inch reflector, but, as a working tool, the latter will possess a great advantage. A small refractor, if a good one, will do wonders, and is a very handy appliance, but it will not have sufficient grasp of light for it to be thoroughly serviceable on faint objects. Anyone hesitating in his choice should look at the cluster about χ Persei through instruments such as alluded to, and he will be astonished at the vast difference in favor of the reflector…. When high magnifications are employed on a refractor of small aperture, the images of planets become very faint and dusky, so that details are lost. pp. 41–42

Later he elaborates on the relative effectiveness of reflectors and refractors: “To grasp details there must be a fair amount of light. I have seen more with 252 on my 10-inch reflector than with 350 on a 5 ¼-inch refractor, because of the advantage of the brighter image in the former case.” p. 49. Author’s note:  How refreshingly honest and insightful Denning is! Having owned and enjoyed a number of smaller refractors of apochromatic and long-focus achromatic pedigree over the years (of 5- and 6-inch aperture), they have all paled in comparison to an 8-inch f/6 Newtonian on virtually all objects (the Sun being a memorable exception) and yet cost many times less. Vanity formed a large part of this author’s recalcitrance to embrace the genius of Newtonian optics, but when given a fair chance (proper acclimation and accurate alignment of the optical train), the refractors left little to be desired. For some, it remains an inconvenient truth that

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a well-executed, mass market 20-cm f/6 reflector would wipe the floor with the finest 5-inch glass on Earth, but it is undoubtedly true. Denning is, however, sympathetic to the casual observer and acknowledges the role a small refractor might play in the pursuit of happy adventures: “Out of door observing is inconvenient in many respects, and those who procure a telescope merely to find a little recreation will soon acknowledge a small refractor to be eminently adapted to their purposes and conveniences.” p. 42. That being said, Denning is careful to qualify this statement with the following: Those who meditate going farther afield, and taking up observations habitually as a means of acquiring practical knowledge, and possibly of doing original work, will essentially need different means. They will require reflectors of about 8 or 10 inches aperture; and if mounted in the open on solid ground, so much the better, as there will be a more expansive view, and a freedom from heated currents, which renders an apartment unsuited to observations, unless with small apertures where the effects are scarcely appreciable. A reflector of the diameter mentioned will command sufficient light grasp to exhibit the more delicate features of planetary markings, and will show many other difficult objects in which the sky abounds. If the observer is especially interested in the surface configuration of Mars and Jupiter he will find a reflector a remarkably efficient instrument. On the Moon and planets it is admitted that its performance is, if not superior, equal to that of refractors. If however, the inclination of the observer leads him in the direction of double stars, their discovery and measurement, he will perhaps find a refractor more to be depended upon, though there is no reason to why a well mounted reflector should not be successfully employed in this branch. pp. 42–43

Author’s note:  Denning’s commentary here resonates very strongly with this author’s field experience. In respect of double stars, the 8-inch Newtonian was found to be a more effective instrument than a custom-made 5-inch f/12 classical refractor, though historically, and inch for inch, there is overwhelming evidence to show that the classical refractor is better suited to resolving binary systems to the limits imposed by their aperture. Indeed, for this exacting task, they remain primus inter pares. Denning feels the images of stars in refractors are better than reflectors: “As far as my own experience goes, the refractor gives decidedly the best image of a star. In the reflector, a bright star under moderately high power is seen with rays extending right across the field, and these appear to be caused by the supports of the flat.” p. 43. Author’s note:  The stellar images in refractors are indeed very pretty, the Fraunhofer diffraction rings being very subdued and sometimes quite invisible on stars of lesser glory. Newtonians show diffraction spikes around bright stellar luminaries, and brilliant planets like Venus present with a singularly peculiar aspect in a moderately large Newtonian. Although this is certainly the case, it is a subjective point. These diffraction spikes appear rather beautiful to some. And while they may bother some individuals, they do not degrade the image in any significant way and can be ignored or unlearned.

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The chapter continues with a brief discussion on telescope testing. Denning’s approach is very down to Earth in this regard. He recommends that one should always try before you buy, especially if the instrument is secondhand. As for the tests themselves, Denning does not recommend the Moon, as it is “too easy,” there being too much wonderful detail on view to sidetrack the observer. Instead he recommends turning the telescope on bright planets, especially Jupiter and Venus, to assess its defining power. Elaborating on Venus, he recommends viewing at dusk or dawn, preferably when the planet has reached a decent altitude. As the magnification is cranked up, the disk of the planet should remain “beautifully sharp and white.” A good telescope ought to hold its definition as the power is increased, with only an enfeebling of light as the image is spread over a larger area. A lesser telescope will show a deterioration of definition under the same conditions, producing a “mistiness” that confuses the definition in a palpable manner. Nor can these errors be ‘focused out.’ Denning also recommends star testing on a second or third magnitude star, the high power image of which ought to be tiny, circular and free from other distortions. If color is seen in a reflector, it is probably the eyepiece and not the telescope that is at fault, though he does not mention the effects of atmospheric refraction that can manifest itself if the object under scrutiny is at a low altitude. He is also careful to distinguish between atmospheric distortion and a bona fide optical fault. Testing even a first rate telescope on a bad night of seeing is sure to produce questionable results, and so these tests ought to be carried out over several nights to be certain of where the problem lies. Denning also mentions the intra- and extra-focal colors of the diffraction rings seen in well corrected achromatic refractors. Author’s note:  It is interesting that Denning does not suggest double stars as a test of telescope optics, in sharp contradiction to many of his contemporaries. In reality though, the resolution of double stars is not a particularly stringent test of optics, as even so-so telescopes will manage some tricky pairs. Such tests are more a measure of atmospheric seeing and transparency than anything else. The best tests are on bright planets, especially Jupiter, which can display a rich variety of low contrast detail that may prove elusive in a lesser instrument and become beautifully manifest in a higher quality telescope. No matter how wonderful or impressive the telescope being employed, without a sturdy mount, its powers will be greatly compromised. Denning considers both alt-­ azimuth and equatorial mounting systems, favoring the latter for high resolution projects, although stressing that high quality work can be also be done with simple non-driven mounts. Mr. Denning estimates that with an undriven, altazimuth mount, roughly 50% of the observer’s time has to be expended adjusting the telescope in order to keep the object centered in the field, particularly if one is examining an object at high magnifications. In the end, though, he cautions that a determined individual can make do with very simple equipment, and, in time, the observer “will gain patience and perseverance which will prove a useful experience in the future.” p. 55.

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Author’s note:  Denning actually opted for simplicity over technical sophistication with his own telescope, a 10-inch With-Browning Newtonian. It was mounted on a good but sturdy alt-azimuth mount, equipped with slow motion controls. By all accounts the instrument was permanently exposed to the elements (as evidenced by comments he made on p. 76), the optics and tube assembly covered over when not in use. Denning’s telescope was thus in a permanent state of acclimation with its environment. No cooling fans were used with the telescope, as they were not available at the time, and indeed, were never really necessary. While some modern amateurs would balk at this modest setup, it pays to remind the reader that Denning established himself as a world authority on planetary observing – particularly Jupiter and Saturn and their satellite systems – contributing a great body of knowledge in the form of drawings and written descriptions of his observations. That Denning chose this setup over something more sophisticated reinforces an old maxim, that the quality of the observer is far more important than the type of equipment employed, a maxim that resonates strongly with this author’s ethos. This is especially true today when the amateur can enjoy high-quality mass-market optics at very reasonable prices. Denning’s estimate of the time lost in active observing must be tempered by the fact that the oculars he employed had very much smaller fields than those typically enjoyed by amateurs today, many of which can cover several times the area of sky he would have routinely encountered, thus reducing the time needed for object centering and adjustment. It is in this chapter also that Denning advances a brief but most engaging commentary on eyepieces: Good eyepieces are absolutely essential. Many object-glasses and specula have been deprecated by errors really originated by the eyepiece. Again, telescopes have not infrequently been blamed for failures through want of discrimination in applying suitable powers. A consistent application of powers, according to the aperture of the telescope, the character of the object, the nature of the observation, and the atmospheric conditions prevailing at the time, is necessary to obtain the best results. p. 46

Denning describes the three most common oculars available to amateurs in his day: the negative, or Huygenian, the positive, or Ramsden, both of which had narrow fields of view and worked best at large relative apertures. He also mentions the Kellner, which afforded much wider fields of view (typically 40° or 50°) for deep sky viewing and decent definition at relative apertures at f/6 and higher. Mr. Denning is skeptical of the claims of some telescope makers and users who have stated that their telescopes can bear powers of up to 100 per inch of aperture: Telescopes are sometimes stated to bear 100 to the inch on planets, but this is far beyond their capacities even in the best condition of air. Amateurs soon find from experience that it is best to employ those powers that afford the clearest and most comprehensive views of the particular objects under scrutiny. Of course, when abnormally high powers are mentioned in connection with an observation, they have an impressive sound, but this is all, for they are practically useless for ordinary work. I find that 40, or at most 50 to the inch, is ample, and generally beyond the capacity of my 10-inch reflector. p. 47

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Author’s note:  Better oculars were invented in the mid to late nineteenth century, particularly the Plossl and orthoscopic, but owing to the greater number of un-­ coated elements, they were not commonly employed by amateur astronomers in Denning’s day. In respect of his comments regarding the 100x per inch claims by some observers and telescope sellers, this was a reasonable conclusion to draw, as one finds from experience that such high powers are indeed disadvantageous to delivering the best planetary images, especially in moderate and large aperture telescopes. Denning finds that 40–50x per inch of aperture to be the maximum upper limit for the vast majority of applications, and this remains true to this day. Indeed, we find that Denning commonly employed a power of 252 diameters on his 10-inch Newtonian in pursuing his studies of the bright planets, corresponding to approximately 25x per inch of aperture, in agreement with the recommendations of the majority of contemporary planetary observers of note. Indeed, it is only in the pursuit of the most difficult double stars and small planetary nebulae that higher powers are found to be useful, and only on the best nights. After these comments, Denning shares with us the details of a curious practice, apparently popular with dedicated observers for at least a century – using a single lens as an eyepiece: A great advantage, both in light and in definition, results in the employment of a single lens as eyepiece. True, the field is very limited, and, owing to the spherical aberration, the objects so greatly distorted near the edges that it must be kept near the centre, but, on the whole, the superiority is much evident. p. 47

Denning informs us that some distinguished observers, such as the Reverend William Rutter Dawes and Sir William Herschel, had also noted an improvement in light grasp and distinctness employing the same technique. Author’s note:  Though we take so much for granted today, with our high quality optical glass, free of striations and other artifacts, broadband multi-coatings and the like, the glass out of which these early oculars were constructed would surely have been inferior to even the ‘budget’ oculars we enjoy today. The complete lack of anti-­ reflection coatings would have generated ghost-images due to internal reflections, especially on bright objects, cutting down on contrast and definition of low contrast details. Adopting a singlet would have greatly reduced these effects at the expense of introducing horrid off-axis aberrations. This author once experimented with a modern ‘ball eyepiece,’ that is, a single, spherical eye lens, and while the definition at the center of the field was very nice, off-axis images were very badly distorted. In the end, he considered it more a novelty than a useful tool and has not used it since. Denning recommends that the observer acquire three eyepieces, corresponding to low, medium and high power, appropriately chosen to match the aperture of the telescope, and cautions that the magnifications they profess to deliver may not in fact be the values they generate. He offers a means of experimentally determining actual magnifications described on pp. 49–50. Denning continues by discussing the curious custom adopted by some telescope makers of using magnifying power as a

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‘sales pitch.’ Surprisingly, Denning identifies the famous maker, James Short (1710–68), as the individual who originated this dubious custom, who made his fortune selling small Gregorian-type reflectors, and which has sadly endured at least for so-called ‘department store’ telescopes right up to the present day. Here is a curious thing. Denning owned a 4-inch Gregorian telescope by Watson, similar to the instrument shown in Figs. 5.11 and 5.12, which, although over a century old at the time, had speculum metal mirrors that were still in good condition. The importance of observing in comfort (pp. 53–54) is a subject very close to Denning’s heart and, accordingly, he stresses the importance of using a chair while observing and even mentions some innovations made by amateurs published in the English Mechanic. He also reveals that for objects located high overhead, a small stepladder was found to be very useful with his 10-inch Newtonian. Comfort is of paramount importance in gaining the maximum enjoyment from an observing experience and can even make the difference between seeing something and seeing nothing at all. Beginning on p. 55 and ending at the top of p. 57, Denning remarks on the ‘character’ of the observer. Variations in visual acuity account for some of the discrepancies reported by observers, as well as their level of experience. Some individuals will see more than others. Historically, these differences have sometimes led to controversy: ….as a rule, amateurs should avoid controversy, because it rarely clears up a contested point. There is argument and reiteration, but no mutual understanding or settlement of the question at issue. It wastes time, and often destroys that good feeling which should subsist amongst astronomers of ever class and nationality…. paltry quibblings, fault finding, or the constant expression of negative views, peculiar to skeptics, should be abandoned, as hindering rather than accelerating the progress of science…. There are some men whose reputations do not rest upon good or original work performed by themselves, but rather upon the alacrity with which they discover grievances and upon the care they bestow in exposing trifling errors in the writings of their non-infallible contemporaries. p. 56

Author’s note:  There is nothing new under the Sun, and Denning’s comments are as true today as the day they were written. Denning himself was the subject of controversy concerning some of his ideas on meteor radiants. He held some erroneous views but was bitterly attacked by some of his contemporaries, just to prove that they were right and he was wrong! They wounded him deeply. This is likely one of the reasons why he withdrew from public life at the height of his career. On p. 58, Denning discusses the practice of stopping down, i.e., the act of deliberately reducing the effective aperture by means of a ‘stop.’ The practice was sometimes done to increase the defining power of the telescope, which, for clarity, we shall equate with image sharpness, but the underlying reason for this was thought by some to be caused by blocking off a defective part of the object glass or mirror. Denning, however, offers us another explanation – the atmosphere and its effects on the fielded aperture. Although it is true that stopping down could mask a figuring error (more likely to occur at the edges of the objective), Denning’s own experiments seemed to favor

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the idea that large apertures can often benefit from stopping down on nights of poor or average seeing because smaller apertures are less affected by atmospheric turbulence than larger ones. He suggests that, for visual use, apertures of 18 inches and over can quite often benefit from an aperture stop of 16 or 14 inches. But he cautions that the practice is of little value in the case of moderate aperture: With my 10-inch reflector, I rarely, if ever, apply stops, for by reducing the aperture to 8 inches the gain in definition does not sufficiently repay for the serious loss of light. But in the case of large telescopes, the conservation of light is not so important, and a 14-inch or 16-inch stop may be frequently employed on an 18-inch with striking advantage. p. 58

In a curious note under the subtitle, ‘Cleaning Lenses,’ Denning tangentially discusses some of the properties of silvered mirrors, in particular, the factors that may prolong the life of the thin silver layer. He notes that keeping the mirror dry is of benefit, as well as placing a protective cap over the optics when not in use. He claims that Calver was aware that some silvered glass mirrors held their reflectance longer than others and was related to the frequency with which the instrument was used and the environment in which it was fielded. Some mirrors held their reflectivity well for a decade or more, but this was apparently the exception rather than the rule. Intriguingly, he also states that the tarnish accumulated on silvered mirrors can work surprisingly well on lunar and planetary targets: A mirror that looks badly tarnished and fit for nothing will often perform wonderfully well. With my 10-inch in a sadly deteriorated state I have obtained views of the Moon, Venus and Jupiter that could hardly be surpassed. The moderate reflection from a tarnished mirror evidently improves the image of a bright object by eliminating the glare and allowing the fainter details to be readily seen. p. 60

Author’s note:  When silver tarnishes it generally leaves a tan colored film owing to the formation of silver sulfide, which can indeed reduce the reflectivity of the mirror, but the moderate deterioration Denning speaks of seemed to enhance his views of the Moon and bright planets. Perhaps this can be attributed to a filter-like or ‘apodizing’ effect. Filters do work superbly well on moderate and large aperture telescopes owing to their ability to suppress glare and enhance the visual appearance of subtle details that would otherwise be ‘washed out’ in the unfiltered image. Indeed, he has previously alerted readers to the benefits of employing a simple and inexpensive neutral density filter to improve the planetary images in large reflectors. More sophisticated filters, such as a polarizer, also work very well in this regard. The Televue bandmate planetary filter was also found to work brilliantly on an 8-inch Newtonian, employed routinely to observe Jupiter. Filters are capable of adding a whole new dimension to the art of visual observing, an effect serendipitously ‘discovered’ by Denning. The remaining pages of this chapter are devoted to miscellaneous topics, including dewing up and cooling down of telescope optics, the celestial globe, presumably a forerunner of the modern planisphere, the utility of opera glasses and finally a brief description of a new type of observatory showing up the length and breadth of the country. Unlike the all-brick, monolithic, cathedral-like domes housing the great

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refractors of the day, Denning indicated that the Romsey offered a much more economical means of housing one’s telescope and keeping all one’s ancillary equipment in a single place.

Chapter IV: Notes on Telescopic Work Covering Pages 66–86 In this invaluable chapter, Denning provides a distillation of his practical experience in the field. He begins by suggesting that the would-be astronomy enthusiast gain some background knowledge of the objects he or she wishes to devote time to. This can be achieved by reading up on the general descriptions provided by trusted authorities in the field. But theory ought to be a guide and not an absolute means to an end, for Denning seems to value practical knowledge over that learned in books: “An observer should take the direction of his labours from previous workers, but be prepared to diverge from acknowledged rules should he feel justified in doing so from his new experiences.” p. 68. Denning feels that the observer ought to be prepared for a night of observing, by making up a suitable list of objects he or she wishes to study. It need not be long or overly elaborate, nor should such a list be overly ambitious. A few objects studied well is far better than several dozen casually visited: When no such preparation is made much confusion and loss of time is the result. On a cloudy, wet day, observers often consider it unnecessary to make such provision and they are taken at a great disadvantage when the sky suddenly clears. A good observer, like a good general, ought to provide, by proper disposition of his means, against any emergency. In stormy weather, valuable observations are often permissible if the observer is prompt, for the definition is occasionally suitable under such circumstances. p. 69

Denning estimates that the British climate offers about 100 h of exceptional seeing per year, considerably more than is commonly cited today; these are not confined to just a few nights but occur sporadically over the course of weeks and months, for he says that a night might start out with decidedly mediocre seeing only to be found to be considerably improved just a few hours later. Denning claims that an east wind is often detrimental to viewing high resolution targets but does not consider this to be an absolute. He differs from the general opinion expressed by contemporary astronomers in claiming that windy weather can often bring very good seeing: I have sometimes found in windy weather after storms from the west quarter, when the air has become very transparent, that exceptionally sharp views may be obtained; but unfortunately, they are not without drawbacks, for the telescope vibrates violently with every gust of wind and the images cannot be held long enough for anything satisfactory to be seen. p. 69

Denning also mentions the favorable conditions that often attend hazy skies: Calm nights when there is a little haze and fog, making the stars look somewhat dim, frequently afford wonderfully good seeing…. The tenuous patches of white cirrus cloud, which

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float at high altitudes, will often improve definition in a surprising manner, especially on the Moon and planets. p. 69

Author’s note:  Denning’s knowledge was gained actively, in the field, more so than any of his contemporaries, for how else could he provide such extraordinary (and mostly correct) insights? Denning’s telescope was in a constant state of preparedness, as it was permanently fielded in the open air. He was thus ready to take advantage of any change in the weather that may have come about and use it to his advantage. Such knowledge cannot be learned from a book. That Denning entrusted experience over theory resonates well with this author’s own findings, especially in relation to double stars, where striking discrepancies between field observations and the prognostications of individuals posing as ‘theorists’ have been uncovered. Indeed, in some of these cases, the differences between theory and experiment have been totally irreconcilable. Beware of theorists posing as observers! Denning next discusses vision and its relation to telescopic observation. He concedes that there is much variation among the visual acuity of individuals, with some displaying remarkable vision and others seeing much less. He mentions a one Dr. Kitchiner, who claimed that the eye of a dedicated telescopist aged 47 is as much impaired as an ordinary individual aged 60! Denning is somewhat skeptical of that claim, though, stating that, “the Doctor’s opinion is not generally confirmed by other testimony, the fact being that the eye is usually strengthened by special service of his character.” Further, he states: Before the observer may hope to excel as a telescopist it is clear that a certain degree of training is requisite. Many men exhibit very keen eyesight under ordinary circumstances, but when they come to the telescope are hopelessly beaten by a man who has a practised eye. On several occasions the writer was most impressed with evidences of extraordinary sight in certain individuals, but upon being tested at the telescope they were found very deficient, both as regards planetary detail and faint satellites. Objects which were quite conspicuous to an experienced eye were totally invisible to them. p. 71

Author’s note:  Denning’s comments agree with the experiences of this author. On many occasions over the years, he has attempted to show his students some of the delights of the heavens, only to discover that, although they have decidedly better eyesight than his own, were nonetheless unable to ‘see’ the duplicity of test double stars, plainly seen with his own eyes. Only after pointing it out and after prolonged scrutiny did they come to ‘see’ what was plainly visible. The same is true of the Great Red Spot. Experience is a far better tool than raw visual acuity. Seeing is most definitely an art that must be learned, as Sir William Herschel perceived long ago. This also has implications for those that have derided the classical achromat, despite an enormous body of evidence demonstrating that users (whose eyes were trained) saw far more than what is commonly reported in the contemporary literature. Indeed they appeared to have seen things that still largely elude the majority of self-proclaimed veterans, calling into question their true status as observers.

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On pp. 72–73, Denning stresses the importance of note taking. The content of these notes need not be elaborate, just a few salient points about the date, time and seeing conditions, the instrument fielded and some brief written details on the objects observed. Denning recommends that such notes be made as close to the time of observation as possible. “If the duty is relegated to a subsequent occasion,” he says, “it is either not done at all or done very imperfectly.” Something ‘trivial’ recorded on an earlier date may turn out to be very important at a later date. Denning also recommends sketching what one sees at the telescope, even if the would-be observer is not skilled in such activities. They need not be works of art but simply show the ‘defining’ features of the object under scrutiny. With time, the note taker/sketcher becomes a “draughtsman”: My own plan in sketching at the telescope is to first roughly delineate the features bit by bit as I successively glimpse them, assuring myself, as I proceed, as to the general correctness in outline and position, then, on completion, I go indoors to a better light and make copies while the details are still freshly impressed on the mind. p. 74

Author’s note:  It is a sad state of affairs that the noble art of note taking is in decline; perhaps terminally. Many amateurs do not take any notes of any description. More’s the pity, for notes provide a means of assessing progress over time, and form the bedrock of an amateur’s experience under the starry firmament. They are an integral part of the culture of amateur astronomy and can prove invaluable in resolving issues that sometimes appear contradictory, especially if one is viewing through different instruments at different times. An observer without notes is liable to make the same mistakes over and over again. Thus, in a very real sense, an observer without notes has no past. Sketching is also an enjoyable and invaluable way of preserving information, and when conducted over a long period of time can prove to be of vital importance, especially if one records something novel. There is no right or wrong way to sketch. Denning preferred to sketch the basic features of his subjects at the telescope, while refining them indoors a short time afterwards. Others choose to scrutinize the object intently, committing to memory all the detail one can capture before returning indoors to do the sketch. Find the method that works best for you. In a section called “Friendly Indulgences,” Denning recognizes the need for outreach and to be gracious to friends and the curious passerby, or anyone who express an interest in viewing an astronomical object. But in the end, he feels that there is a fine line between getting on with one’s observing and being a showman. One comes away with the feeling that he was, for the most part, a solitary observer, who was happy in his own company and would rather get on with things than engage in some lengthy discussion with someone else while the sky remained clear: Of course it is the duty of us all to encourage a laudable interest in the science, especially when evinced by neighbours or acquaintances; but the utility of an observer constituting himself a showman, and sacrificing many valuable hours which might be spent in useful observations, may be seriously questioned. The weather is so bad in this country that we can ill spare an hour from our scanty store. p. 74

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Author’s note:  One cannot help but wonder what Denning would have thought of the star parties amateurs attend these days. I suspect he would have kept well away from them. Although star parties can be fun and provide a means of looking through various kinds of telescopes to assist making a decision on a future purchase, this hobby is still, by and large, a solitary pastime. We must remember that for every lion among us there is also a leopard. Denning discusses the realities of open air observing, wittily commenting that a shiny new telescope tube exposed to the elements of nature will soon lose its “smart and bright appearance,” although the views will remain as good as they always were. It is here also that the forgotten Bristolian reveals his great love affair with the heavens, providing vivid descriptions of the physical conditions he had to endure night after night. Because he remained a bachelor all his life and thus had no dependents, his world could best be likened to that of a monk, wedded, as it were, to his astronomical investigations. As a dedicated meteor observer, Denning spent endless hours on every clear night recording their brilliant tracks across the sky. This kind of work is not for the faint hearted, especially in the cold of winter. Denning describes his lot vividly: Night air is generally thought to be pernicious to health; but the longevity of astronomers is certainly opposed to this idea. Those observers who are unusually susceptible to affections of the respiratory organs must of course exercise extreme care, and will hardly be wise in pursuing astronomical work out of doors on keen, wintry nights. But others, less liable to climatic conditions, may conduct operations with impunity and safety during the most severe weather. Precautions should always be taken to maintain a convenient degree of warmth; and for the rest, the observer’s enthusiasm must sustain him. A “wadded dressing gown” has been mentioned as an effective protection from cold. I have found that a long, thick overcoat, substantially lined with flannel, and under this a stout cardigan jacket, will resist the inroads of cold for a long time. On very trying nights, a rug may also be thrown over the shoulders, and strapped round the body. During intense frosts, however, the cold will penetrate (as I have found during prolonged watches for shooting stars) through almost any covering. As soon as the observer becomes uncomfortably chilly, he should go indoors and warm his things before a fire. p. 75

After relating many humorous stories about finding ‘wee beasties’ taking up residence inside his telescope tube, Denning returns to more pressing matters, emphasizing that an observer eager to discover something of importance must necessarily be a person of method and perseverance and not to divest too much importance to his instruments: “A skilled workman will do good work with indifferent tools; for after all it is the character of the man that is evident in his work; and not so much the resources which art places in his hand.” p. 80. Author’s note:  The old adage is true: a bad workman always blames his tools! Today, we are blessed to have vastly superior tools to anything Denning could have dreamed of. And yet, all the while, we seem to want more and more. Fortunate indeed is the person who is happy with his or her tools! In the final pages of this interesting chapter, Denning discusses the potential of photography to revolutionize the science of astronomy. His opinions are brief, but

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he was essentially correct about its growing prowess. Since very few amateurs had the means of conducting photographic studies of the heavens at that time, though, he does not dwell on the topic. The author encourages his readers to follow the astronomical literature, and recommends all the greats of the age, including the Reverend T. W. Webb’s Celestial Objects for Common Telescopes, Chamber’s Descriptive Astronomy and Noble’s Hours with a 3-Inch Telescope, as well as more specialized texts. He also encourages his readers to consult practical periodicals of the day, especially the English Mechanic, Nature and Knowledge. Denning encourages those who live in towns and cities to get out and do some observing, explaining that the conditions can be quite good, especially for viewing the Moon and the planets. He mentions that smoggy conditions may actually aid in bringing out detail on the planetary bodies: “I have frequently found planetary markings very sharp and steady through the smoke and smog of Bristol. The interposing vapours having the effect of moderating the bright images and improving their quality.” p. 81. He ends this chapter on an enthusiastic note: A telescope may either be employed as an instrument of scientific discovery and critical work, or it may be made a source of recreation and instruction. By its means the powers of the eye are so far assisted and expanded that we are able to conceive of the wonderful works of the Creator than could be obtained in any other way. p. 86

Author’s note:  The population of Bristol, where Denning lived for most of his life, quintupled during the nineteenth century, reaching 330,000 by 1901. The burning of coal would have been the main source of energy driving commerce and heating households, and so smog would have been a common phenomenon, especially during still winter nights in the city. Denning yet again mentions the beneficial effects of dimming the image as regard to gleaning more defining power from planetary bodies. Were he alive today, Denning would probably have been an enthusiastic proponent of filters in planetary astronomy. Unbridled enthusiasm distinguished Denning from many of the classic authorities of his day. His tone was approachable, unpretentious and reassuringly upbeat.

Chapter V: The Sun Covering Pages 87–112 We now begin to explore the late nineteenth century knowledge of the heavenly bodies, one by one, beginning with the Sun. As a guide, this author will bring to bear his experiences with a telescope not too dissimilar to Denning’s own – an 8-inch f/6 Newtonian on a modern alt-azimuth mount, which has given him wondrous views of the firmament (Fig. 19.2).

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Fig. 19.2  Denning Crater, Mars. (Image courtesy of Wiki Commons. https://en.wikipedia.org/ wiki/Denning_(Martian_crater)#/media/File:Dennin_Crater_Floor.JPG)

The opening pages of this chapter discuss basic solar facts, as true today as they were in Denning’s time. The Sun, we learn, has a mean distance from Earth of about 92,900,000  miles, computed from a solar parallax of 8.8″, and a diameter of 866,000  miles. Interestingly, Denning provides a series of micrometer measures (p. 88) of the solar disk diameter, showing that it varies from 32 min 66 s at the end of December to 31  min 32  s at the end of June. This reflects the slight elliptical nature of Earth’s orbit, carrying our planet slightly closer to the Sun in mid-winter in the Northern Hemisphere and a little further away in mid-summer. Denning relates the fact that the most conspicuous features of the solar disk – sunspots – were likely seen throughout antiquity, and among observers from a number of civilizations. The earliest account offered by Denning dates to a. d. 188. These spots were seen by the naked eye through dense fog, most commonly at sunrise and sunset. Denning himself speaks of observing four large spots (p. 89) on a foggy autumnal evening in 1870, just as the Sun was setting. He claims that if these spots are bigger than about 50″, they should be picked up by the average eye. Author’s note:  Although a curious visual phenomenon, this author strongly advises that the reader not look at the Sun even in the very foggy conditions described above. Many a tyro has damaged his or her eyes in doing so. Denning is reluctant to attribute the telescopic ‘discovery’ of sunspots to any one individual but mentions, in particular, various early telescopists, including Fabricius, Galilei, Harriot and Scheiner, as claiming the limelight. He also corroborates later accounts by historians of astronomy, who claim that England’s Thomas Harriot saw these spots telescopically as early as December 8, 1610: “The altitude of the Sonne being 7° or 8°, and it being a frost and a mist, I saw the Sonne in this manner.” p. 90.

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Denning also mentions a drawing made by Harriot, showing three large sunspots. Thus, Denning was probably aware of Harriot’s early telescopic observations, possibly predating those made by Galileo. The most common way in which observers in Denning’s day observed the Sun was to employ deeply colored glass of various depths, either red or green, placed at the focal plane, together with a Herschel wedge, invented in 1830 by Sir John Herschel. Denning claims that red tinted glass is inferior to its green tinted counterpart: “The diagonal, by preserving a part only of the solar rays, which are transmitted by the object glass. This little instrument is comparatively cheap, and no telescope is complete without one.” p. 92. Denning suggests that a small telescope, a refractor of 3- or 4-inch aperture, or a reflector of no more than 4 inches, are best employed in solar studies and recommends that larger instruments be stopped down to improve definition. He also mentions, owing to the great natural brilliance of the Sun, that unsilvered mirrors are perfectly adequate for obtaining good solar images. With comfort and safety never being far from the mind of the author, Denning stresses that the solar observer be shaded from the Sun’s burning rays as much as is practical. He also recommends keeping the ‘solar telescope’ in the shade to ensure it does not induce the annoying thermals that can destroy high-definition features. As regard to suitable magnification, he suggests that a power of about 60 and a field of view of just over half an angular degree is desirable to get a good ‘whole disk’ perspective. Higher powers can prove useful to gain better images of smaller features, though he does not recommend magnifications higher than about 150x. Once again, Denning mentions using a singlet eyepiece (presumably the field lens of a Huygenian ocular) in obtaining high power views yielding the highest definition. Oddly enough, Denning gives scant mention to other methods of observing the solar disk, particularly by projecting the image onto a smooth, white surface. There is one reference made to this technique, appearing on pp. 93–94: At Stonyhurst Observatory excellent delineations of solar phenomena are made; and the late Father Perry, who lost his life in the cause of science, thus described the method: – “On every fine day the image of the Sun is projected on a thin board attached to the telescope, and a drawing of the Sun is made, 10 1/2 inches in diameter, showing the position and outline of the spots visible. pp. 93–94

Solar projection techniques were used by the very earliest telescopists, including Galileo. In a most curious account related on p. 95, Denning describes the use of a primitive reticle scale, just a graduated piece of plain glass, mounted at the focal plane of a 4-inch Cooke refractor, borrowed from a friend, with which he was able to estimate the size of a large sunspot observed on June 19, 1889. Using this technique he calculated that the real size of the spot was 27,000 miles! This technique could also be done using projection methods. Author’s note:  How wonderful it is to be able to measure anything! Denning was no mathematician, of course, but he did have an excellent command of numbers, as we shall see in many other references explored later in the book.

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The chapter continues with discussions on various solar phenomena, beginning with the majesty of a solar eclipse, briefly describing their prediction (saros cycles) and rarity at any arbitrarily chosen location. On p. 98, the aspects of a series of 12 partial solar eclipses as seen (or imagined) from England through the years 1891 to 1922, are reproduced. This is followed by an equally brief discussion on the sunspot cycle and how it may be followed by the amateur with modest equipment. Another Curious Aside  In his younger years, Denning was a keen hunter of the hypothetical planet Vulcan, explaining why he had a particular interest in all things solar. Indeed, he helped organize coordinated searches with a number of English solar astronomers. Moreover, in Chapter IV, p. 85, he made two lists of (I) ‘suspected objects to be erased,’ and (II) ‘objects that in the future will add to our store.’ Vulcan appears in the former list, suggesting that, at the time of writing of the book, he had firmly given up on the prospect of finding an intra-Mercurial planet. The quest for Vulcan reached fever pitch in Europe and across the United States during the late nineteenth century, bolstered by the work of mathematical (but myopic) astronomers of the ilk of (the arrogant) Urban Leverrier (1811–77), who uncovered a small, residual perihelion shift in the position of the planet Mercury, amounting to 43 arc seconds per century. Indeed, a hitherto obscure physician and amateur astronomer named Edmond Modeste Lescarbault (1814–94) claimed to have observed such a planet in March 1869 at his private observatory in the picturesque village of Orgères-en-Beauce, in northern France. Leverrier was happy to accept him as the discoverer and formally named the planet Vulcan  – after the Roman god of fire  – in March 1860, which supposedly circled the Sun every 19.7 days, at a distance of about 21 million km from the solar surface. But soon, the astronomical community grew skeptical of Lescarbault’s sensational ‘discovery,’ claiming that such a world, even though as small as the Moon, would have been easily visible to many astronomers who had watched the Sun for many years. By the time Denning penned his wonderful tome, most astronomers had dismissed the notion that a ninth planet, Vulcan, really existed, even though the reason for the measurable 43″ per century perihelion shift of Mercury was not yet accounted for. The explanation had to wait until Albert Einstein formulated his epochal theory of general relativity in 1915, which perfectly accounted for the Mercury anomaly. Indeed, Einstein was to later write that his heart raced when his calculations exactly explained the planet’s sojourn through the curved space near the Sun. “For a few days,” he wrote, “I was beside myself in joyous excitement.” From pp.  100–112, Denning goes on to describe, in considerable detail, the telescopic morphology of sunspots as well as their distribution on the solar surface. He provides an accurate and essentially modern value for the solar rotation period of about 25 days and 8 h. It was also known to him that the rotation period varies with solar latitude, thus providing good evidence (like Jupiter, discussed later) for its essentially gaseous nature. On p. 105, Denning presents a list of historically interesting astronomers and their estimates of the solar rotation rate from Cassini (1678) to Wilsing (1888), showing that such knowledge was known for nearly two centuries.

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Denning displays his voluminous knowledge of solar phenomena in these closing pages of Chapter V, including the work of many astronomers – both contemporary and historical – as well as some of his own detailed observations carried out with a 4-inch glass. This includes a discussion on solar faculae, prominences and historically significant eruptions, as well as some observational anomalies including spots noted at unusually high solar latitudes: “Mechain saw a spot in 1780 having a latitude of 40 1/3°; in April 1826 Cappoci recorded one having 49° of S. latitude Schwabe and Peters observed spots 50° from the equator. Lahire, in the last century, described a spot as visible of 70°; but the accuracy of this observation has been questioned.” p. 111. Finally, on p. 112, Denning provides a curious reference to a quantitative brightness differential between the solar limb and its center, a measure previously unknown to this author: In observing the Sun with a telescope the amateur will soon notice that the surface is far more brilliant in the central parts than round the margin of the disk. Vogel has estimated that immediately inside the edges the brightness does not amount to one seventh that of the centre. The difference is entirely due to the solar atmosphere, which is probably very shallow relatively to the great diameter of the Sun. p. 112

Author’s note:  The Sun is, by and large, composed of a fourth form of matter known as plasma. At temperatures in excess of a few thousand Kelvin, atoms break up to form a ‘soup’ of charged particles consisting of electrons, protons and an assortment of atomic nuclei. It is this moving ‘plasma’ that generates the Sun’s prodigious magnetic field and all its associated phenomena.

Chapter VI: The Moon Covering Pages 113–136 Early in autumn, when the evenings are frequently clear, many persons are led with more force than usual to evince an interest in our satellite, and to desire information which may not be conveniently obtained at the time. The aspect of the Moon at her rising, near the time of the full, during the months of August, September, and October, is more conspicuously noticeable than at any other season of the year, on account of the position she then assumes on successive nights, enabling her to rise at closely identical times for several evenings together. The appearance of her large, ruddy globe at near the same hour, and her increasing brilliancy as her horizontal rays give way under a more vertical position, originated the title of “Harvest Moon,” to commemorate the facility afforded by her light for the ingathering of the corn preceding the time of the autumnal equinox. p. 113

It is with such wonderful prose that Denning opens his chapter on observing our closest neighbor in space. Denning was a man happy to be in the open air, either with telescope, a field glass, or with his unaided eyes, observing the grand spectacles of the heavens. In the preceding paragraphs, he clearly outlines why the Moon is of such critical importance to life on Earth, in issuing the tides, for example, and stabilizing Earth’s climate. But he also notes its importance, since time immemo-

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rial, in human time keeping, as well as how its welcome light assisted the plight of navigators of the seven seas. What follows thereafter are some basic physical facts about the Moon. For example, he states the apparent size of the Moon at apogee and perigee (29′21″ and 33′5″, respectively), though he appears to have mistakenly stated these the wrong way round on p. 114. The lunar diameter he quotes – 2160 miles – and its mean distance from Earth – 237,000 miles – are essentially those of the modern value. Denning then launches into a general overview of the lunar regolith as seen through a good telescope: When we critically survey the face of the Moon with a good telescope, we see at once that her surface is broken up into a series of craters of various sizes, and that some irregular formations are scattered here and there, which present a similar appearance to mountain ranges. The crateriform aspect of the Moon is perhaps the more striking feature, from its greater extent; and we recognise in the individual forms a simile to the circular cavities formed in slag or some other hard substances under the action of intense heat. In certain regions of the Moon, especially near the south pole, the disk is one mass of abutting craters, and were it not for the obvious want of symmetry in form and uniformity in size, the appearance would be analogous to that of a giant honeycomb. These craters are commonly surrounded by high walls or ramparts, and often include conical hills rising from their centres to great heights. While the eye examines these singular structures, and lingers amongst the mass of intricate detail in which the whole surface abounds, we cannot but feel impressed at the marvellous sharpness of definition with which the different features are presented to our view. It matters not to what district we direct our gaze, there is the same perfect serenity and clearness of outline. Not the slightest indication can be discerned anywhere of mist or other obscuring vapours hanging over the lunar landscape. pp. 114–115

Denning correctly states that the Moon is devoid of an atmosphere and probably doesn’t have water, in spite of the many ‘seas’ that adorn lunar maps. On pp. 115 through 116, Denning presents an explanation for why the Moon shows the same face toward Earth throughout its cycle (it is almost completely tidally locked) and presents the interesting phenomenon of libration, where the lunar countenance can show up to 59% of its surface over the course of its orbit about Earth. Denning also mentions the wonderful phenomenon of earthshine, the “new Moon in the old Moon’s arms,” and how the observers of old remarked that a waning Moon showed this earthlight more strongly than the new Moon. The chapter continues by discussing the kinds of instruments best suited to lunar work, for the casual as well as the more serious observer: A small instrument with an object glass of about 2 ½ inches will reveal a large amount of intricate detail on the surface of our satellite, and will afford the young student many evenings of interesting recreation. But for a more advanced survey of the formations, with a view to discover unknown objects or traces of physical change in known features, a telescope of at least 8 or 10 inches is probably necessary, and powers of 300 to 350, and more. p. 118

Author’s note:  Yet again, Denning dispenses sterling advice to the would-be student of the Moon that is entirely in agreement with all subsequent authorities on the subject. You’ll see more with a larger telescope and will be able to use higher powers to ferret out the finer details. Such advice appears to have been lost on a current

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subsection of amateurs who are willing to squander a veritable fortune for small refractors of very limited aperture. Such are the times we live in! On pp. 118 and 119, Denning discusses the fascinating phenomenon of a lunar eclipse, their frequency and appearance, both telescopically and to the naked eye. Here we find some invaluable historical records of how the intensity of a total lunar eclipse varied from apparition to apparition, with references to observations conducted by astronomers dating back nearly nine centuries. Although some total lunar eclipses were spectacularly bright, with a beautiful, coppery orb being clearly visible to the naked eye, at other times, the eclipsed Moon completely disappeared: On May 5, 1110, Dec.9, 1620, May 18, 1761, and June 10, 1816, our satellite is said to have become absolutely imperceptible during eclipse. Wargentin, who described the appearance 1761, remarks: – “The Moon’s body disappeared so completely that not the slightest trace of any portion of the lunar disk could be discerned, either with the naked eye or with a telescope. p. 119

Denning recalls his observations of a peculiarly dim lunar eclipse: On Oct. 4 1884, I noticed that the opacity was much greater than usual; at a middle period of the eclipse the Moon’s diameter was apparently so much reduced that she looked like a dull, faint, nebulous mass, without sharply determinate outlines. The effect was similar to that of a star or planet struggling through dense haze. p. 119

In contrast, Denning describes the eclipse of March 19, 1848, as unusually bright: “The Moon presented a luminosity quite unusual. The light and dark places on the face of our satellite could be almost as well made out as an ordinary dull moonlight night.” p. 119. In addition to these records, Denning mentions some explanations for the variability of the intensity of such eclipses. In particular, he describes a theory first suggested by the great German astronomer and mathematician Johannes Kepler, who attributed this variability to differences in the humidity of the atmosphere, as well as more contemporaneous explanations proffered by a one Dr. Burder, who attributed such changes to the activity of the solar corona. Author’s note:  Denning did not mention the considerable effects of atmospheric dust, which has a known reddening effect on astronomical bodies, e.g., sunsets, owing to a phenomenon known as Rayleigh scattering. His description of the unusually dim appearance of the lunar eclipse of October 4, 1884, could be explained by the volcanic eruption of Krakatoa, Indonesia, in August 1883, which would have ejected a considerable mass of dust into Earth’s upper atmosphere, causing freak meteorological conditions well into 1884. Our satellite presents such a wealth of intricate detail through a Newtonian of moderate aperture that it is scarcely possible to describe the impact with which it assaults the eye on a clear and tranquil night. The images of the Moon at moderate and high power through an 8-inch f/6 Newtonian would have been broadly comparable to what Denning saw and recorded so diligently that it is possible, at least to some degree, to relive the visual extravaganzas he remarks upon in the subsequent pages of his chapter on our faithful satellite in space.

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Although there is little doubt in Denning’s mind that the Moon is, to all intents and purposes, geologically dead, he is of the opinion, like so many other dedicated lunar observers before and after him, that changes can and do occasionally occur on its surface. Pp. 120 through 123 recount a number of observations carried out by historical figures concerning this perennially interesting subject, beginning with the views of Sir William Herschel, who conducted extensive lunar observations using his “most excellent” 6.3-inch Newtonian reflector of 7-foot focus. On p.  120 he reproduces Herschel’s lunar observations, dated to April 1787: “I perceive three volcanoes in different places of the dark part of the New Moon. Two of them are already nearly extinct, or otherwise in state of going to break out, the third shows an eruption of fire or luminous matter.” p. 120. But other observers soon offered less far-fetched explanations of these ‘fiery’ structures, particularly Schröter, who in fact used an identical 7-foot reflector to that employed by Herschel, suggesting they were due to reflected light from Earth falling upon elevated spots and having “the unusual capacity to return it.” Denning’s contemporary, Wilhelm Tempel, of comet fame, reported what he thought was an impact of some sort on the evening of June 10, 1866, near the locus of the great crater Aristarchus: “Of course,” he wrote, “I am far from surmising a still active chemical outbreak, as such an outbreak supposes water and an atmosphere, both of which are universally not allowed to exist on the Moon, so that the crater-forming process can only be thought of as a dry, chemical, although warm one.” p. 121. On the same page, Denning recounts the extraordinary tale of the German astronomer Johann Friedrich Julius Schmidt (1824–1885), who claimed that the ­5.5-mile-­diameter crater Linné had completely disappeared in 1866: “He averred that he had been familiar with the object as a deep crater since 1841 but in October 1866 he had found its place occupied by a whitish cloud. This cloud was always visible but the crater itself appeared to have become filled up, and was certainly invisible under its former aspect.” p. 121. Denning discusses the observations of other observers, who took Schmidt’s report seriously, but in the end, the lack of confirmation led him to think that it was a trick of the light. On p. 122, he also relates the case of a one Dr. Klein, who, in contrast to Schmidt, reported the actual appearance of a “deep, dark crater” – about 18 miles to the west-northwest of Hyginus! This time, Denning himself had a look at the region with his 10-inch With-Browning Newtonian, but like many of his contemporaries, described it as a “saucer like depression” rather than the “sharply cut, deep crater” described by Klein. Authors note:  Schmidt’s observations caused international controversy for several decades, drawing the attention of many astronomers of repute. But while Schmidt had established himself as a careful and experienced observer, in the end the case was considered unproven. It is now known that the visibility of this crater is highly dependent on seeing conditions, being all but invisible under poor atmospheric conditions. Throughout the twentieth century, a sizable fraction of lunar observers continued to search for so-called transient lunar phenomena (TLP), which basically refer to

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any sudden changes to the lunar surface and which have a scientific basis in meteorite impacts, lunar out-gassings and the like. The lunar enthusiast is encouraged to keep reporting such anomalies when they occur. But you need to get outside and actually look at the Moon! In the next section, Denning brings our attention to the importance of timing when it comes to observing high resolution objects on the lunar surface: “As the Sun’s altitude is constantly varying with reference to lunar objects, they assume different aspects from hour to hour. In a short interval the same formations become very dissimilar.” p. 122. Furthermore, Denning offers the reader some excellent advice, which, sadly, is not at all stressed by contemporary lunar observers: The lunar landscape must be studied under the same conditions of illumination and libration, with the same instrument and power, and in a similar state of atmosphere, if results are to be strictly comparable. But it is very rarely that observations can be effected under precisely equal conditions; hence discordances are found amongst the records. p. 123

What follows on from this is an excellent summary of the most prominent lunar visual spectacles, together with brief notes on what can be observed with a modest telescope. The importance of note taking is once again stressed, especially the local time to the nearest minute. The text is illustrated by some exquisite drawings of T. Gwyn Elger (and reproduced quite well in this inexpensive reprint!). On p. 135 Denning discusses the occultation of stars by the Moon, which, he reminds us, occur several times each month! Here he mentions something rather curious: The stars do not always disappear instantaneously. On coming up to the edge of the Moon they have not been suddenly blotted out, but have appeared to hang on the Moon’s limb for several seconds. This must arise from an optical illusion, from the action of a lunar atmosphere, or the stars must be observed through fissures on the Moon’s edges. p. 135

The reader is encouraged to find out how the discussion develops! Author’s note:  One gets the strong impression that Denning was an advocate of the volcanic origin of the lunar craters, a theory that was supported well into the twentieth century. This is despite the fact that the impact theory of crater formation was alive and well ever since the time of Dr. Robert Hooke (1635–1703), who was among the first to suggest the latter as a plausible, alternate theory, based on experimental science.

Chapter VII: Mercury Covering Pages 137–144 In the opening paragraphs of this chapter, Denning identifies Mercury as the closest planet to the Sun, though he still gives mention to the elusive planet Vulcan, discussed previously in connection with the our nearest star. He then presents the

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basic astronomical information about Mercury, including its orbital period, eccentricity, elongations, true and apparent diameter, which, he informs us, varies from 4.5- to 12.9 seconds of arc at superior and inferior conjunction, respectively. These data are essentially modern. Denning also mentions the curious fact that the great Polish astronomer, Nicolaus Copernicus, never once saw Mercury! “Copernicus, amid the fogs of the vistula, looked for Mercury in vain, and complained in his last hours that he had never seen it!” p. 138. Following on from this, Denning discloses the number of sightings of the planet he made at this point in his astronomical career: I have seen Mercury on about sixty-five occasions with the naked eye. In May 1876, I noticed the planet on thirteen different evenings, and between April 22 and May 11, 1890, I succeeded on ten evenings. I believe that anyone who made it a practice to obtain naked-­ eye views of this object would succeed from about twelve to fifteen times in a year. p. 139

He then follows up with details of particular apparitions of Mercury, as preserved in his voluminous notes, when the planet was particularly bright and striking to the eye, such as in February 1868 and in November 1882. Author’s note:  It is probably true that many an amateur astronomer has never observed Mercury, owing to its very low altitude and proximity to the Sun. Denning was a prodigious observer, though, and the number of sightings he mentions pays testimony to that precocity. With characteristically delightful prose, Denning describes the momentous first sighting of the planet in the telescope and the excitement it induces in the observer: The first view of Mercury forms quite an event in the experiences of many amateurs. The evasive planet is sought for with the same keen enthusiasm as though an important discovery were involved. For a few evenings efforts are in vain, until at length a clearer sky and a closer watch enables the glittering little stranger to be caught amid the vapours of the horizon. The observer is delighted and, proud of his success, he forthwith calls out the members of his family that they, too, may have a glimpse of the fugitive orb never seen by the eye of Copernicus. p. 139

After presenting further historical tidbits, he then describes the general appearance of the little planet as it appeared through his telescope; Mercury has a dingy aspect in comparison with the bright white lustre of Venus. On May 12, 1890, when the two planets were visible as evening stars, and separated from each other by a distance of only 2 degrees, I examined them in a 10-inch reflector, power 145. The disk of Venus looked like newly polished silver, while that of Mercury appeared of a dull leaden blue. A similar observation was made by Mr Nasmyth on September 28, 1878. The explanation appears to be that the atmosphere of Mercury is of great rarity, and incapable of reflection in the same high degree as the dense atmosphere of Venus. p. 140

Author’s note:  Although some observers have reported a pinkish tint to the planet over the years, this is indeed reminiscent of the appearance of the planet seen in various telescopes over a few decades of time by this author. Regarding Mercury’s lack of an appreciable atmosphere, Denning’s conclusion is absolutely sound. Any primordial air it might have had has long been stripped away by the solar wind.

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What remains now is an extremely nebulous vapor, consisting mostly of the ions of the alkali and alkaline Earth metals. Continuing on in this chapter, Denning discusses the ways in which the enthusiast may derive the maximum amount of information from this small and somewhat elusive world. With his simple, un-driven mount, he advises the would-be observer to catch the planet just before dawn and to carefully follow it as it rises higher in the sky. He refrains from making any detailed studies until a few hours after rising, however, when the disk takes on a much steadier appearance. During these better moments, he most likens Mercury to the planet Mars in terms of the dark markings and spots it presents to the trained eye. For this he employed a power of about 212 diameters with his 10-inch silver-on-glass reflector. On pp. 141–2, Denning reproduces the details of a correspondence he had with the famous Italian astronomer, G.  V. Schiaparelli (of Mars fame) in 1882, who, using a fine 8.5-inch Merz achromatic refractor, agreed wholeheartedly with Denning that Mercury most resembles the Red Planet, at least superficially. Two fine drawings of the planet made by the Bristolian observer himself are presented on p. 143. Denning further discloses details of Schiaparelli’s belief that the length of Mercury’s day is the same as its orbital period, in the same way as our Moon. He does, however, stress that these details still required corroboration. The final pages of the chapter discuss transits of the planet as well as an occultation of Mercury by the Moon, dating to April 25, 1838. Author’s note:  Schiaparelli’s claims about the length of a Mercurial day were not ultimately borne out. The planet in fact takes twice as long to revolve on its axis (176 days) as it does to complete one orbit of the Sun (88 days). However, this was not determined until 1965 using radar techniques.

Chapter VIII: Venus Covering Pages 145–154 Denning begins this chapter by commenting on the illustrious beauty of Venus as it presents in the sky at dawn or at dusk, and how many of the ancients believed the morning and evening stars were not one and the same. As harbinger of the day, Venus was known as Lucifer by the ancient Greeks, and Hesperus, when the planet appeared as an evening star. When it appeared as an evening object in the autumn of 1887, Denning informs us that many people thought that the Star of Bethlehem had returned after a hiatus of nineteen centuries! He explains that at its greatest brilliancy, the planet is reduced to a slender crescent subtending an angular diameter of 65″ at inferior conjunction. And when displaying its full disk, it shrinks in both size and luminous glory, presenting a disk scarcely one seventh as large (9.5″). As anyone who has examined Venus with telescopic aid will attest, the planet can be disappointing:

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When the telescope is directed to Venus it must be admitted that the result hardly justifies the anticipation. Observers are led to believe, from the beauty of her aspect as viewed with the unaided eye, that instrumental power will greatly enhance the picture and reveal more striking appearances than are displayed on less conspicuous planets. But the hope is illusive…. There are no dark spots, of bold outline, such as we may plainly discern on Mars, visible on her surface. There is no arrangement of luminous rings, such as encircle Saturn. There are no signs of dark variegated belts, similar to those that gird Jupiter and Saturn; nor is there any system of attendant satellites, such as accompany each of the superior planets. pp. 146–7

Nonetheless, Denning concedes that Galileo’s observations of the phases of Venus through his primitive telescopes were enough to put the Copernican principle on a firm footing. As with observing Mercury, he recommends that Venus is best observed during the day. He then launches into a brief survey of historical observations of the planet by celebrated observers of past centuries including J. D. Cassini (1666), Bianchini (1726–7), Schröter (1788) and Sir William Herschel (1777–93), and observations made in his own century including, Mädler (1833) and Di Vico (1840–1). Denning recounts in detail some observations conducted by Schröter, who thought that Venus had enormous mountains, the peaks of which would occasionally penetrate the clouds and reveal their presence in the telescope. Like Mercury, the rotation period of Venus was unknown in Denning’s day and varied enormously from 23 h, 21 min (Cassini 1666) to 224.7 days (Schiaparelli 1880). Author’s note:  Schiaparelli was the closest to getting Venus’ rotation period correct. At 224 days it was less than 20 days short of the modern determined value of 243  days. He deduced this time period by assuming that the planet was tidally locked, owing to its closer proximity to the Sun than Earth. We now know that Venus rotates in a retrograde direction, a result of a possible collision with a large embryonic planet early in the history of the Solar System. Beginning on pp. 150 through 151, Denning discusses the nature of the many faint markings detected by observers over the years. He notes that many of these reports were made by astronomers using rather small telescopes and how observers endowed with the visual acuity of the Reverend Dawes, failed to detect any markings with the telescopes they employed. He cautions that small telescopes will often create illusory views: Perhaps it may be advisable here to add a word of caution to observers not to be hastily drawn to believe the spots are visible in very small glasses. Accounts are sometimes published of very dark and definite markings seen with only 2 or 3 inches aperture. Such assertions are usually unreliable. Could the authors of such statements survey the planet through a good 10- or 12-inch telescope, they would see at once they had been deceived. Some years ago I made a number of observations of Venus with 2-, 3- and 4 1/2 inch refractors and 4and 10-inch reflectors, and could readily detect with the small instruments what certainly appeared to be spots of a pronounced nature, but on appealing to the 10-inch reflector, in which the view became immensely improved, the spots quite disappeared, and there remained scarcely more than a suspicion of the faint condensations which usually constitute the only visible markings on the surface. p. 151

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Denning gives mention to one of Venus’ most mysterious and enduring phenomena, referred to today as the Ashen Light; a faint ‘ashy light’ similar to earthshine seen on the Moon, when the planet is near inferior conjunction and its slender crescent is most prominently displayed. He refers to the kind of illumination as a ‘phosphorescence.’ He reports that Mr. Zanger, based in Prague, observed a ‘coppery ring’ completely encircling the planet on a number of occasions. Author’s note:  The ashen light has a very long history associated with it, dating back to the mid-seventeenth century. One of the finest astronomical artists of the post-war era, Richard Baum, of Chester, England, produced some wonderful renderings of the Ashen Light using his beloved old 4.5 Cooke refractor. The remainder of the chapter discusses alleged observations of a satellite of Venus dating from the seventeenth and eighteenth centuries. The putative Cytherean moon, unofficially named ‘Neith,’ was never positively identified and the consensus among astronomers of the nineteenth century was that the earlier sightings were nothing more than an ignis fatuus resulting from ghost reflections from eyepieces and the like. Curiously, Denning mentions the transits of Venus which occurred in 1874 and 1882, which he himself observed and even mentions the ‘future’ transit of 2004, which would thrill a new generation of astronomers. Author’s note:  It is noteworthy that Denning completely avoids speculating on the nature of the Cytherean environment, particularly in light of the wild speculations that were doing the rounds in the late Victorian period. Back in 1870, his compatriot, Richard A. Proctor (1837–88), embracing Darwinian ideology, thought nothing of considering Venus as the abode of life: It is clear that, merely in the greater proximity of Venus to the sun, there is little to render at least the large portion of her surface uninhabitable by such beings as exist upon our earth. This undoubtedly would render [the sun’s] heat almost unbearable in the equatorial regions of Venus, but in her temperate and subarctic regions a climate which we should find well suited to our requirements might very well exist … I can find no reason … for denying that she may be considered the abode of creatures as far advanced in the scale of creation as any which exist upon the earth.

Many of Denning’s contemporaries thought it a certainty that life exists on other planets. Today, many more scientists are conceding that this may not be the case, especially in light of how complex living things appear to be and the utter failure of naturalistic models to explain the origin of life.

Chapter IX: Mars Covering Pages 155–166 Mars is the fourth planet in order of distance from the Sun. He revolves in an orbit outside that of the Earth, and is the smallest of the superior planets. His brilliancy is sometimes considerable when he occupies a position near to the Earth, and he emits an intense red

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light, which renders his appearance all the more striking. Ordinarily his lustre does not equal that of Jupiter, though when favourably placed he becomes a worthy rival of that orb. In 1719 he shone so brightly and with such a fiery aspect as to cause a panic. The superstitious notions and belief in astrological influences prevailing at that time no doubt gave rise to the popular apprehension that the ruddy star was an omen of disaster, and thus it was regarded with feelings of terror. Fortunately, the light of science has long since removed such ideas from amongst us, and celestial objects, in all their various forms, are contemplated without misgiving. They are rather welcomed as affording the means of advancing our knowledge of God’s wonderful works as displayed in the heavens. p. 155

In line with previous chapters, Mr. Denning summarizes the main physical data associated with the Red Planet, which is essentially modern. Mars can vary enormously in its apparent size, from 4″ when it is near conjunction with the Sun, swelling to over 30 s of arc at opposition. It has been known since the time of Galileo that Mars can present with a prominent gibbous phase. When it is furthest from the Earth, Denning reminds us that it is only large, observatory class telescopes can make out any significant details on Mars, but as it approaches opposition it can become a ‘magnificent object’ worthy of scrutiny even with the smallest of optical instruments. He advises that meaningful observations conducted by amateurs should really only be done in the weeks leading up to and immediately following opposition. Denning is clearly aware that the Martian atmosphere is very rarefied in comparison to our own world and thus its surface features are relatively easy to delineate in a modest telescope. The discussion then develops with a mention of some seminal historic observations conducted by his astronomical forebears, most notable of which are Fontana, Cassini and Huygens, who came up with pretty astonishing measures of the rotation period of the planet (now called a sol), which demonstrated that a Martian day was only a little longer than the Earth. Denning mentions the intense white patches seen at the planet’s poles but still cautions to call them “polar snows.” A drawing of the planet as it appeared to Denning on the evening of April 13, 1836, appears on p.  157 using his 10-inch Newtonian, power 252x. On p. 158 of the text, Mr. Denning describes the long tradition of Martian map-­ making, that is, aerography, conducted by many of his diligent predecessors, including the work of Maraldi, Herschel, Schröter, Madler, Schmidt and Dawes, whose names adorned the earliest Martian maps available to amateur astronomers. Darker regions were almost invariably associated with ‘seas,’ and the brighter sections, ‘continents,’ indicating that these early telescopists were keen to impress a sense of the familiar to the planetary images they studied with their instruments. By the time he was penning the words of this text (c. 1890), Denning humorously quips that the naming of new Martian features had been reduced to the level of farce: A few years ago, when christening celestial formations was more in fashion than it is now, a man simply had to use a telescope for an evening or two on Mars or the Moon, and spice the relation of his seeings with something in the way of novelty, when his name would be pretty certainly attached to an object and hung in the heavens for all time! A writer in the ‘Astronomical Register’ for January 1879 humorously suggested that “the matter should be put into the hands of an advertizing agent” and “made the means of raising a revenue for

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astronomical purposes.” Some men would not object to pay handsomely for the distinction of having their names applied to the seas and continents of Mars or to the craters of the Moon. pp. 158–9

Author’s note:  How ironic! Denning was almost prophetic about the “cash for names” culture that would grow up in modern times. No need for the learned astronomer; one can now purchase one’s own star! My eldest son had a star named after him – a well-meaning gift from a friend – though he wasn’t too impressed when he saw it through a telescope! On pp. 159 through 160, Mr. Denning discusses the ‘recent’ discovery of the two diminutive satellites of Mars, discovered by Professor Asaph Hall using the 25.8 inch Washington refractor in 1877. These eluded the eye of both Sir William Herschel, who undoubtedly used large enough instruments to detect them, as well as the astronomers who employed the great 72-inch Leviathan of Parsonstown. Denning doesn’t provide any real explanations for this anomaly but may well have been attributed to the fact that the great refractor was mounted on a state-of-the-art, clock-driven equatorial mount, which helped to stabilize the images of the planet from moment to moment and was most ably suited to studying images for prolonged periods. Denning also discusses the interesting phenomenon of the Martian “canals” [Denning’s emphasis] as observed by G. V. Schiaparelli, beginning in the winter of 1881, together with their evolution into ‘duple’ structures by the summer of 1890. Curiously, while Denning does mention a few other individuals who saw the canals, he himself does not emphatically admit seeing such structures (see page 160). Perhaps the most illuminating confirmation of the Martian canals comes from Denning’s compatriot, the lawyer and amateur planetary observer, A.  Stanley Williams of Brighton, who recorded no less than 43 such structures, seven of which were clearly double, and all using only a 6.5-inch Calver reflector employing powers between 320 and 430, though magnifications below 300 were deemed useless. Author’s note:  That Williams was able to employ powers of and in excess of 50x per inch of aperture using his 6.5 inch Calver bears some testimony to the underlying quality of its optics; a point well borne out by my discussions with a few contemporary observers who have restored such instruments to functional use. Having said all that, Denning does provide his recommendations concerning the size of telescope that will provide fine, high magnification details of the Red Planet under favorable conditions: “Rather a high power must be employed  – certainly more than 200; and if the telescope has an aperture of at least 8 inches, the observer will be sure to discern a considerable extent of detail.” pp. 162–3. Denning divides Martian surface phenomena into a number of categories: • Seas, which he defines as dark areas, some of which can be picked up with apertures as small as 1.5 inches. He mentions the excellent work of Charles Grover, who started his career with very small instruments. • Lighter areas that surround the ‘seas’ which can extend for hundreds of miles.

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• Irregular streaks, condensations and veins, which, to some degree or other may appear linear. He does suggest however that on a night of good seeing, these linear structures resolve into ‘spots.’ (p. 161) • Atmospheric features owing to Mars’ thin but still appreciable sea of air, some of which can be traced right the way to the limbs of the planet. Denning presents still more invaluable information concerning measures of the rotation period of the Red Planet as estimated by a dozen or so astronomers dating from the mid-seventeenth century. Although all of these estimates are very accurate, it is curious that Sir William Herschel got closest to the modern accepted value as early as 1784, a full century before Denning penned this work. He includes his own value of 24 h, 37 min and 22.34 s reduced from data collated from 15 years of observations made from his home in Bristol [see footnote on p. 162]! The remainder of this interesting chapter covers some historical sightings of the satellites of Mars- Deimos and Phobos. Denning notes that no sooner had Asaph Hall discovered them with the 25.8 inch Washington Refractor, that a suite of other sightings were reported using much smaller instruments; some as diminutive as 7.3 inches! This seems all the more incredulous considering that at greatest elongation from the planet, Phobos and Deimos shine feebly at magnitudes + 11.5 and + 13.5, and are separated from the Martian limb by a mere 12″ and 32,″ respectively. Finally, Denning mentions some notable historic occultations of Mars on p. 166. Author’s note:  The 165-km-wide Martian crater, Denning, located at 17.7° south latitude and 326.6° west longitude in the Sinus Sabaeus quadrangle, has been named in honor of the great British observer.

Chapter X: The Planetoids Covering Pages 167–169 In this very short chapter, Mr. Denning describes the state of affairs of asteroid discoveries made up until that time and their location, orbiting some 2–4 times further out from the Sun than Earth, between the orbits of Mars and Jupiter. He recounts the elucidation of Ceres by Piazzi in 1801 and a few of the brighter asteroid discoveries in the decades that followed. Denning discloses that at the time of writing (c.1890), some 300 planetoids had been discovered at a rate of about six per annum, though many more were yet to be discovered. The largest and brightest of these are visible in common, backyard telescopes but they are not the most exciting objects to observe owing to their diminutive size and faintness. Denning wisely suggests that on-going searches for asteroids be conducted by properly equipped observatory-­ class instruments. On p. 168 Denning makes this interesting remark: “A real variation of light has been assumed to occur, but this is not fully proved.” p. 168. Author’s note:  Denning alludes to the possibility that the asteroids vary in brightness. Today we know that asteroids rotate and thus display different surfaces to the

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sunlit side facing the Earth. These surfaces will often have differing albedos, thereby explaining the variation in brightness. Today, though astronomers estimate that millions of asteroids exist, only 60 or so have sizes larger than about 60 kilometres and about 750,000 have sizes of the order of 1 kilometer. Most of the asteroids uncovered during Denning’s lifetime were between magnitude 10 and 12. Asteroids are thought to represent the left over debris from the formation of the solar system, some 4.6 billion years ago.

Chapter XI: Jupiter Covering Pages 170–194 Of all the planets, Jupiter is the most interesting for study by the amateur. It is true that Saturn forms an exquisite object, and that his wonderful ring-system is well calculated to incite admiration as a feature unique in the solar system. But when the two planets come to be repeatedly observed, and the charm of first impressions has worn away, the observer must admit that Jupiter, with his broad disk and constantly changing markings, affords the materials for prolonged study and sustained interest. With Saturn the case is different. His features are apparently quiescent; usually there are no definite spots upon the belts and rings. There is a sameness in the telescopic views; and this ultimately leads to a feeling of monotony, which causes the object to be neglected in favour of another where active changes are in visible progress. p. 170

William Denning was arguably the most experienced observer in the world at the height of his astronomical career. Having clocked up thousands of hours conducting naked eye observations of meteors, telescopically scanning the sky for comets (of which he was the discoverer of five such bodies), and providing regular and highly detailed views of the planets, his opinions were well sought after by the best professional astronomers of the day. In regard to planets, it was arguably the giant world, Jupiter, that captivated his imagination most strongly, and for reasons he makes clear in the opening paragraph of the chapter quoted above. It is therefore no small wonder that he dedicated 24 pages to its study. Denning’s renderings of Jove were referenced in every authoritative work on the planet over the past century. For serious work on Jupiter, Denning used his 10-inch silver-on-glass reflector, the drawings from which were widely disseminated in the popular publications of the day. These and other archives show that he employed the same instrument to continue his Jupiter studies for a full decade after he penned his magnum opus. Denning’s interest in Jupiter appeared to be mostly scientific in nature. As we have seen with the other planets, he spent long hours making estimates of the rotation of these bodies, Jupiter included. But in making such observations, he picked up many fine details of this complex and rapidly changing world, the characteristics of which have been confirmed to exist in the modern age. After describing the various belts and zones that can be seen though a good telescope, Denning, as usual, never fails to acknowledge the outstanding work of his forebears in establishing many of the basic facts often taken for granted by his con-

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temporaries [and his descendants too]. On p.  172, he mentions that the earliest detection of distinct belts girdling the planet was made by “Zucchi” as early as 1630. Undoubtedly, Denning was referring to the Italian Jesuit priest and astronomer, Niccolo Zucchi(1586–1670), who made many important contributions to the science of optics, even proposing that concave mirrors could replace lenses to focus light as early as 1616. As we have seen, it was astronomers such as Robert Hooke and G.D. Cassini, using the long focus non-achromatic refractor, who were amongst the first to see definite spots on the planet, allowing them to make good estimates of Jupiter’s rotation period. Denning informs us that it was Cassini who first noted that spots located at different Jovian latitudes appeared to rotate at different degrees of celerity; the higher the latitude the slower the rate of rotation. Cassini measured this discrepancy to about 6 min, while Sir William Herschel, observing a century later, whittled it down to nearer 5 min. Author’s note:  The phenomenon of differential rotation, that is, when different parts of a body rotate at different rates, is indicative of the non-solid makeup of the body under study and can readily be observed by amateur telescopes on the Sun, Jupiter and Saturn. Differential rotation is the reason why Jupiter observers acknowledge different systems of longitude on the planet: System I, which defines the longitude of the equatorial region, rotates at a rate of 9 h 50 min and 30.003 s, while System II longitude, covering the higher latitudes (both north and south), has a period of 9 h 55 min and 40.6 s. Beginning at the bottom of p.  173 and continuing through to 175, Denning engages in a fascinating discussion on arguably Jupiter’s most interesting phenomenon; the Great Red Spot. He describes how this enormous elliptical shaped feature has changed dramatically in size and color intensity over the years (as evidenced by many of his own superlative drawings of the Jovian disk). During the late nineteenth century, the spot was enormous: “From measures at Chicago, in the years 1879 to 1884, Prof. Hough found that the mean dimensions of the spot to be:- Length 11″.75, breadth 3″.71. These figures represent a real length of 25,900 miles and a diameter of 8200 miles. The latitude of the spot was 6″.97S” p. 174. Author’s note:  What invaluable information we have here! How else might we obtain such knowledge? The Great Red Spot (GRS) has been shrinking throughout the twentieth century. During NASA’s Voyager spacecraft flybys in 1979, it had a major axis of 14,500 miles and a Hubble Space Telescope measure made in 1995, showed it to be only 13,020 miles across. Finally, in 2009, it had to shrink still further to just 11,130 miles. This author’s own telescopic observations over the years has also confirmed that it is both decreasing in size as well as rapidly losing its elliptical shape, and is more circular than it has been in living memory. No one knows precisely why this is the case, but since we do know it is a massive storm system, it must lose energy as it ages and thus, we may be witnessing its slow demise. Is the Giant Planet in the process of losing its most iconic telescopic feature? Will it be visible to future generations? Time will tell!

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Mr. Denning, like many of his contemporaries, used the GRS to obtain estimates of the rotation period of Jupiter. On page 175 however, he does present some intriguing data which show significant changes in the rotation rate of the same feature. Author’s note:  It is not at all clear whether Denning was altogether aware of the possibility that the GRS itself was not fixed in longitude, but in fact slowly drifts over time. The interested reader should consult the later work of Bertrand M. Peek, who, in his book, The Planet Jupiter; An Observer’s Handbook(1958) provides some excellent graphical data showing just how much the GRS has drifted in longitude over time (1851–1935) on page 153 of the text. Because atmospheric features such as the GRS are not fixed in longitude, they cannot ultimately be relied upon to arrive at the best rotation period measures for the planet. Today planetary scientists have abandoned all such approaches, relying instead upon the rotation of the Jovian magnetosphere as the most reliable method of deriving the planet’s rotation period. This so-called System III method, presents a rotation period of 9 h 55 min. After discussing the usual Jovian features such as spots, barges, belts and zones, Denning returns to the GRS and speculates on why, over the years, its color intensity varied so much with the passing of the years. On p. 179, he offers a fascinating, and, as far as this author is aware, unique explanation of his own: My own opinion of the spot is that it represents an opening in the atmosphere of Jupiter, through which, in 1872–82, we saw the dense red vapours of his lower strata, if not his actual surface itself. Its lighter tint in recent years is probably due to the filling-in of the cavity by the encroachment of durable clouds in the vicinity. p. 179

Author’s note:  Denning was incorrect about claiming to see the ‘surface’ of the planet. But his explanation of why the GRS varied in color intensity is very imaginative and is at least scientifically plausible. In other literary sources we learn that Denning believed the spot to sink and soar periodically in the Jovian atmosphere, causing it to fade and intensify over time. This idea has fallen out of favor with planetary scientists today, however. Instead they propose that the brick red color of the spot is due to the complex interactions of cyano compounds with sunlight. Other researchers have implicated sulfur- and phosphorus-rich molecules upwelled from deep within the Jovian atmosphere. On p. 178, he provides a plate of Jupiter drawings made by some of the finest British observers of Jupiter of the age including Dawes, Huggins, Joseph Gledhill, as well as one presented by Denning himself. Curiously, the drawings show considerable detail that are broadly comparable between observers. Historically speaking, Dawes was in possession of a fine 7.5-inch Clark refractor at the time the drawing was recorded, Huggins employed a slightly larger 8.25-inch Clark object glass, and Gledhill probably used a similarly sized equatorial refractor to conduct his sketches (dated to 1870 and 1872). Denning devotes the next few pages to discussions concerning other bright and dark equatorial spots and peculiar changes to the belt system of the planet as

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described by a variety of historically significant observers. This is followed by some general advice to the would-be student of the Giant Planet: Drawings of Jupiter obtained under the highest powers that may be employed with advantage, and with a cautious regard to faithful delineation, will probably throw much light on the phenomena occurring in the planet’s atmosphere. And it is most desirable to pursue the various markings year after year with unflagging perseverance; for it is only by such means that we can hope to unravel the extraordinary problem which their visible behaviour offers for solution. Too much stress cannot possibly be laid on the necessity of the observers being as precise as possible in their records. The times when an object comes to the central meridian should invariably be noted; for this affords a clue to its longitude, and a means of determining its velocity. Its position N. and S. of the equator, should be either measured or estimated; and alterations in tone, figure or tint described, with a view to ascertain its real character. p. 183

Author’s note:  A modern 8- or 10-inch reflector will show a wealth of detail on Jupiter, quite comparable to the drawings recorded on page 178 of Denning’s tome. Some of the finest contemporary renditions of Jupiter can be seen in the work of Dr. Paul Abel, a British astronomer by profession, but also a keen amateur planetary observer, who uses an equatorially mounted, SkyWatcher 8-inch f/6 Newtonian to conduct all his superlative planetary drawings. In the remainder of this fascinating chapter, Denning extols the virtues of observing the many fascinating satellite phenomena associated with Jupiter. A table presented on p.  188 gives some of the basic physical data of the Galilean satellites (abbreviated I to IV in order of distance from the planet). Their measured angular diameters (ranging from 0.91 to 1.49″) agree well with modern figures. What is more, they were all large enough for Denning to record them as discernible disks with his 10-inch With-Browning reflector, even when they are located to one side of the planet or the other. Denning states that Sir William Herschel was amongst the first to observe differences in albedo in the Galilean satellites, particularly in observations carried out between 1794 and 1796. Denning attributes these differences to real surface features: “Spots exist on the surfaces of these objects, and probably occasion many of the differences observed.” p. 189. On p.  193, Denning provides still more historical details of observers who recorded distinct markings on the Galilean satellites: Spots have been seen on the satellites both in transit and while shining on the dark sky. This particularly refers to III and IV. II has never given indications of such markings on its bright uniformly clear surface. Dawes, Lassell and Secchi frequently observed and drew spots. Secchi described III as similar in aspect to the mottled disk of Mars as seen in a small telescope; his drawings exhibit no analogy, however, to those of Dawes of the same object. III. has been remarked as a curious shape, as if dark spots obliterated part of the limbs. Sat I. was observed in transit on Sept. 8, 1890 by Barnard and Burnham, and it appeared to be double, being divided by a bright interval or belt. They used a 12-inch refractor, powers 500 and 700, and the seeing was very fine. p. 193

Author’s note:  In retrospect, it is not at all surprising that surface details on satellite II were not forthcoming, owing to its diminutive size (0.91″) and its smooth

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ice-covered surface. Denning also notes the observations of E. E. Barnard and S. W. Burnham who were able to use powers of 500 and 700x on a 12-inch Clark refractor, providing further evidence of their optical prowess in sharp contradistinction to the prognostications of the ‘forum culture’ of the post-modern amateur, who has been blinded by his/her commitment to materialism.

Chapter XII: Saturn Covering Pages 195–214 The globe of Saturn is surrounded by a system of highly reflective rings, giving to the planet a character of form which finds no parallel among the other orbs of our solar system. His peculiar construction is well calculated to be attractive in the highest degree to all those who take delight in viewing the wonders of the heavens. Saturn is justly considered one of the most charming pictures which the telescope unfolds. A person who for the first time beholds the planet, encircled in his rings and surrounded by his moons, can hardly subdue an exclamation of surprise and wonder at a spectacle as unique as it is magnificent. Even older observers, who again and again return to the contemplation of this remarkable orb, confess they do so unwearyingly, because they find no parallel elsewhere; the beautifully curving outline of the symmetrical image always retains its interest, and refreshes them with thoughts of the Divine Architect who framed it! The luminous system of rings attending this planet not only gratifies the eye but gives rise to entertaining speculations as to its origin, character, and purposes with regard to the globe of Saturn. Why, it has to be asked, was this planet alone endowed with so novel an appendage? And what particular design does it fulfil in the economy of Saturn? It cannot be regarded as simply an ornament in the firmament, but must subserve important ends, though these may not yet have been revealed to the eye of our understanding. pp. 195–6

In these opening lines of Chapter 12, Denning lays bare the palpable sense of fascination with Saturn and its glorious ring system as revealed by the power of the telescope. Denning clearly felt the Solar System was designed purposefully, to reflect the glory of an all-powerful Creator, as well as to delight and stimulate the mind of man. Author’s note:  Despite the fact that astronomers have uncovered several thousand exoplanets in exotic stellar systems, none matches our Solar System in the precise arrangement of its planets. And though journalists are very quick to suggest that some of these exoplanets are habitable, no hard evidence of life has been forthcoming. Denning was not aware that other planets exhibit ring systems albeit, very faint ones, including Jupiter and Uranus, which were not discovered until well into the age of robotic space exploration. One the great joys of reading older authors of astronomy is that they can provide brand-new insights and factual information that has been lost in the mists of time. As commented on previously, Denning was very meticulous in his presentation of historical information as introductory material for his chapters on visual observing. One gains the strong impression that he felt it right and honorable to note, albeit

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briefly, the achievements of those observers who came before him, and to include the comments of his contemporaries, even if they did not accord with his own. For example, we all know that G. V. Cassini discovered the famous division in the ring system that bears his name. But can anyone inform this author of the conditions under which he made these observations? Neither could this author until he stumbled across an account reproduced on page 198, where he learned that the Cassini Division was discovered in twilight! And Denning tells us that he gets this information from Dr. Smith’s Optics (1738), who recounted the story thus: In the year 1676, after Saturn had emerged from the Sun’s rays Sig. Cassini saw him in the morning twilight with a darkish belt upon his globe, parallel to the long axis of his ring as usual. But what was most remarkable, the broad side of the ring was bisected right round by a dark elliptical line, dividing it, as it were, into two rings, of which the inner ring appeared brighter than the other one, with nearly the like difference in brightness as between that of silver polished and unpolished- which, though never observed before, was seen many times after with tubes of 34 and 20 feet, and more evidently in twilight or moonlight than in a darker sky. p. 198

Author’s note:  Although this is ‘secondary source’ material, of course, it is nonetheless thrilling to ‘discover’ a historical morsel like this popping up in the pages of Denning’s tome. This author spends a considerable amount of time each year observing in twilight conditions, and enjoys finding things in twilight. He can also vouch that lunar and planetary images can look magnificent in twilight. Incidentally, as already mentioned, Denning was a keen observer by day and by night. Indeed, if the date of the Jupiter drawing made by Denning, and reproduced below, is correct, modern computer programs can show us that he must have observed it in a bright sky! But to what extent, if anything, is Cassini’s assertion that his celebrated Division can be seen better in twilight? Is there any science to back that up? It would be good to investigate this interesting assertion.

An Aside: A Great Old Telescope Dr. Jim Stephens, based in Mississippi, USA, kindly sent me a link to an antique With-Browning reflecting telescope, owned by Robert A.  Garfinkle FRAS.  The instrument, a 8-inch f/7.5 silver-on-glass speculum, was originally owned by Edmund Neison (1851–1938), who passed it on to Thomas Gwyn Elger (1838–97), who passed it on to Walter Goodacre (1856–1938), who passed it on to Hugh Percy Wilkins (1896–1960) before being acquired by Garfinkle. These individuals were accomplished and highly respected lunar observers in their day. This instrument would have been very similar to that employed by Denning in his surveys of the sky. The reader will note the mirror was re-silvered and tested at Kitt Peak, where its accuracy was estimated to be about 1/25 wave; not bad at all for an antique

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Newtonian and a testimony to the kind of quality available to those Newtonian users of old. Denning, as a world class authority on the planet Saturn, discusses many curious phenomena recorded by observers, both historical and contemporary. For example, on page 200 Denning states that only two relaible determinations of the planet’s rotation period had been made; the first by Sir William Herschel dating to 1793, who provided a value of 10 h and 16 min, and another almost a century later by Professor Asaph Hall, who estimated Saturn’s day length to be 10 h 14 min. Denning informs us that both observers had estimated these timings by following the progress of bright and dark spots in the upper atmosphere of the planet. Curiously, he also notes that Hershel made an earlier estimate of 10 h 32 min and 15 s. Author’s note:  The modern accepted value for the length of a Saturnian day is 10 h, 39 min and 22 s, which is especially close to Herschel’s measure. It never ceases to amaze how astonishingly close this celebrated astronomer from antiquity did this using equipment most modern observers would turn their nose up at. On pp. 201 through 205, Denning launches into a most fascinating discussion on Saturn’s rings, reminding us of facts that are all too often forgotten, such as the greater brightness of the inner ring (with the Cassini division providing the cut off) in comparison with the outer. On page 201, he states that the angular width of the Cassini division is 0.4″ which translates to a real width of 1700  miles. He also brings to our attention the remarkable fact that very small telescopes are able to see this division, such as a report by Charles Grover, who observed it clearly with a 2 inch refractor (see a note towards the bottom of page 209 for reference). Author’s note:  The actual width of the Cassini division is dependent upon where it is measured in respect of the planet. At its widest extent, it is about 0.75″ but is significantly narrower as it is measured along an imaginary line running through its central meridian. That said, Denning was clearly aware that on an extended object at least, angular resolution was considerably better than that attributed to double star measurement. The Dawes limit for a 2-inch aperture, for example, being 4.57/2 = 2.29″. Two splendid drawings of Saturn accompany the text; one made by the distinguished Belgian observer F. Terby (p. 203) and another on page 201, by Denning himself (with his 10 inch reflector, power 252 diameters). Both reveal great skill in their execution, showing not only the celebrated Cassini division but also the Crepe ring and the Encke division in the outer ring. Extensive banding on the globe is also recorded in both drawings. On p.  204, in a section entitled Discordant Observations, Denning brings our attention to the dangers of attributing too much to telescopes of very small aperture: It is curious that the details of Saturn have occasioned more dissension amongst observers than those of any other planet. This may have partly arisen from the great distance of Saturn, the comparitive feebleness of his light, and complexity of his structure. The planet is usually better defined than either Mars or Jupiter; but with tolerably high powers on small instruments the image is faint, and features so diluted that the impressions received

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cannot always be depended on, especially when the air is unsteady. A fluttering condition of the object is sufficient in itself to cause deception. p. 204

Author’s note:  As Denning reminds us, small telescopes run out of light quickly and, as a result, many details that can readily be seen in larger aperture instruments will prove much more elusive in smaller telescopes. Beware of observers who produce seemingly wondrous details on planets in small aperture telescopes under unfavorable and/or low altitude conditions! Denning provides an excellent overview of the Saturn’s magnificent satellite system, at least, as was then known. Small telescopes can show several quite well; Titan, Tethys, Rhea, Iapetus and Dione, can be seen well in a 4-inch refractor. Enceladus, Denning informs us, can be seen with moderate aperture, but b­ ackground stars are often mistaken for it. When the rings are presented edge on, good opportunities are afforded to observe satellite eclipses and can be observed with telescopes of modest aperture. On p. 205, he reproduces a very nice sketch recorded by a one Mr. Capron who observed Titan in transit across the face of the planet on the evening of December 10, 1877, using a 8.25-inch reflector, power 144 diameters. A Curious Endnote  Denning did not discuss the physical nature of Saturn’s ring system. In particular, whether they were solid structures or made up of many smaller, composite particles. This interesting question was addressed by the great Scottish physicist, James Clerk Maxwell, in a most brilliant paper published in 1859. In this paper, Maxwell showed conclusively that were Saturn’s rings solid, they would be rapidly torn apart by Saturn’s enormous tidal forces.

Chapter XIII: Uranus and Neptune Covering Pages 215–26 By the time Denning penned his marvelous tome in amateur astronomy (1891), the discovery of Uranus was over a century in the past, but as one will see from the opening pages of this chapter, it stimulated a great deal of discussion among observers and whether or not it was misidentified by many astronomers before the time of Herschel. As you’d expect, Denning does a good job recounting the details of Herschel’s gradual realization that he had discovered a whole new world beyond the orbit of Saturn, but also some curious details of how it was repeatedly missed by earlier observers: “Flamsteed observed it on six occasions between 1690 and 1715, while Le Monnier saw it on 12 nights in the years from 1750 to 1771, and it seems to have been pure carelessness on the part of the latter which prevented him from anticipating Herschel in one of the greatest discoveries of modern times.” p. 216. Though it was undoubtedly seen throughout antiquity owing to its faint visibility (magnitude 6) to the naked eye, details concerning its visual appearance had to await access to telescopes of sufficient power. Coupled with a small mean angular

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size of 3.6″ and comparative faintness, many seasoned observers of the nineteenth century found it difficult to see any surface markings on the planet, with many, including William Lassell, working with a 2-foot speculum metal reflector in Malta (1862), reporting either a bland disk or, at best, faint banding. Further observations conducted with some of the large refractors at Nice (30 inch), France (1889), and the 23-inch equatorial refractor (1883) at Princeton the United States seemed to affirm the presence of equatorial banding on the planet. But what is particularly revealing is the lack of any accurate determination of the planet’s rotation period, with estimates of anything between 10 and 14 h. That such uncertainty persisted concerning the latter provides solid evidence that the markings on Uranus were of an extremely faint nature and required quite powerful telescopes and considerable patience to discern. Denning himself alludes to the difficulty of observing such banding: “With my 10 inch reflector I have suspected the existence of the belts, but under high powers the image is too feeble to exhibit delicate forms of this character.” p. 219. Author’s note:  The modern accepted value for Uranus’ rotation period is 17  h 14 min. This author has never observed banding with a fine 5-inch f/12 achromatic refractor, and has (possibly) glimpsed one or two of them in a modern 8 inch Newtonian, though the consensus of opinion gravitates toward a 12 inch as about the minimum aperture needed to see these features with any certainty. It is made clear to the reader that Uranus was strongly tilted on its axis was not at all apparent at the end of the nineteenth century when Denning penned his tome, though he does mention some wildly discordant results obtained by the French observers, M. Perotin, working with the great Nice refractor, and the brothers Henry at the Paris Observatory. The former noted only a small (10°) tilt of the planet relative to the common plain of the orbits of its satellites, whilst the latter estimated the value to be 41°! Author’s note:  These data only serve to compound the singular difficulty of observing Uranus, even with large, observatory class telescopes. No consensus could be made regarding its tilt (really 97°) owing to the difficulty in observing this small and faint planet far from the warming rays of the Sun. Denning notes that the motions of the then four known satellites of Uranus showed that they orbited in retrograde (see p. 221), but a little note of clarification is needed here: the planet itself, like Venus, orbits in a retrograde sense (as seen from the north pole of the Sun), but its satellites have orbits that are prograde with respect to Uranus itself. In the aftermath of some cataclysmic event in its early history, Uranus was set “rolling its way,” as it were, around the Sun; in sharp contradistinction to all the inner worlds of the solar system, which spin like tops as they move in their orbits. Denning dedicates the remainder of the chapter to Neptune, which, as one can imagine, is presented as even more mysterious than Uranus. After providing an excellent overview of the historical details of the discovery of the planet (involving

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Messrs Le Verrier, Adams and Galle), Denning does offer us a fascinating account of how the planet was seen half a century before them (1795) by Lalande: It was found that the planet was previously observed by Lalande on May 8 and 10 1795, but its true character escaped detection. This astronomer had observed a star of the same star in the exact place noted on the former evening, he rejected the first observation as inaccurate and adopted the second, marking it doubtful. Had Lalande exercised discretion, and confided in his work, he would hardly have allowed the matter to rest here. A subsequent observation would have at once exhibited the cause of the discrepancy, and the mathematical triumph of Le Verrier and Adams, half a century later, would have been forestalled. p. 223

Author’s note:  Hindsight is a wonderful thing, is it not? Denning informs us that the telescopic sight of Neptune is far from inspiring. Our knowledge of this distant orb is extremely limited, owing to his apparently diminutive size and feebleness. No markings have ever been sighted on his miniature disk, and we can expect nothing until one of the large telescopes is employed in the work. No doubt this planet exhibits the same belted appearance as that of Uranus, and there is every probability that he possesses a numerous retinue of satellites. In dealing with an object like this, small instruments are useless; they will display the disk, and enable us to identify the object and determine its position if necessary, but beyond this their powers are restricted by want of light. p. 223

Author’s note:  Denning’s surmising concerning this distant planet has been proven to be well founded. Owing to its tiny size (2.7″ at opposition) it is never much to write home about and is indeed a rather lackluster telescopic sight. Yet it does exhibit belts (and spots) like that of its sibling, Uranus. Indeed, planetary scientists group these worlds together as ‘icy giants’ of the Solar System, and even show up in a number of extrasolar planetary systems thus far characterized by astronomers. On p. 223, Denning does mention William Lassell’s idea that Neptune may have a very faint ring system but is skeptical as to its veracity in light of the limited observations made with large telescopes at the time of writing of his book. Lassell did however discover Neptune’s largest satellite, Triton, just 17  days after the planet itself was discovered. With a maximum elongation only 18″ from Neptune, this 14th magnitude would have been most difficult to pinpoint, and is thus a testimony to the skills employed by its discoverer. On p. 224, Denning presents a very curious paragraph exploring the possibility of trans-Neptunian planets! He mentions, in particular, the theoretical work of a one Professor Forbes, who wrote a memoir in 1880 “tending to prove that two such planets exist.” Author’s note:  There is nothing new under the Sun! Astronomers have long entertained the idea that more worlds lie beyond our ken than we can ‘see’ with the telescopes we devise. Such discoveries continue apace in the twenty-first century.

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Chapter XIV: Comets and Comet Seeking Covering Pages 227–59 Supersitious ideas with regard to comets as the harbingers of disaster have long since been discarded for more rational opinions. They are no longer looked upon with as ill omened presages of evil, or as: “From Saturninus sent, to fright the nations with a dire portent.” Many refernces are to be found among old writings to the supposed evil influence of those bodies, and the dread which their appearance formerely incited in the popular mind. Shakespeare makes an allusion to the common belief; “Hung be the heveans with black, yield day to night! Comets, importing chance of time and states, Brandish your crystal tresses in the sky;” and in relation to the habit of connecting historical events with their apparition, he further says; When beggars die, there are no comets seen; The heavens themselves blaze forth the death of princes.” But happily, the notions prevalent in former times have been superseded by the more enlightened views naturally resulting from the acquirement and diffusion of knowledge; so that comets, though still surrounded by a good deal of mystery, are now regarded with considerable interest, and welcomed, not only as objects devoid of malevolent character, but as furnishing many useful materials for study. Mere superstitions have been set aside as an impediment to real progress, and more intelligent age has recognized the necessity only with facts and explaining them according to the laws of nature; for it is on facts, and their just interpretation that all true searches after knowledge must lie. Comets are properely regarded as bodies which, though far from being thoroughly understood in all the details of their physical structure and bahaviour, have yet a wonderful history, and one which, cold it be clearly elucidated, would unfold some new and marvellous facts. pp. 227–8

William Denning was not only a world class planetary observer; he was also the discoverer of several comets viz, 1881V, 1890VI, 1892 II and 1894 I, and with the exception of the comet discoveries Holmes and E Hind, the only bodies of such kind unveiled since the time of Caroline Herschel. Denning independently found Comet 1891 I less than 24 h after it was first seen by the great American astronomer, E. E. Barnard. To find a comet takes a great deal of commitment, of course, invariably requiring many hundreds or thousands of hours of sweeping the skies at dusk and dawn in the hope that a new icy interloper would find its way into the field of view of his telescope. Indeed, Denning’s tally of comet discoveries was not rivaled until much later into the twentieth century, when the remarkable George Alcock, added to Britain’s prestige for finding these curious celestial interlopers. In this chapter, we gain a unique glimpse of the state of scientific knowledge regarding comets in the late nineteenth century, as well as the methods which were employed in their detection. Almost immediately, we gain the unmistakable impression that Denning found observing comets to be a particularly exciting pastime, and his enthusiasm proves infectious: Whilst its grand appearance in the firmament arrests the notice of all classes alike, and is the subject of much curious speculation amongst the uninformed, its merits, apart from

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other considerations, the most assiduous observation on account of the singular features it displays and the striking variations they undergo. Indeed, the visible deportment of a comet during its rapid career near perihelion is so extraordinary as to form a problem, the solution of which continues to defy the most ingenious theories. The remarkable changes in progress, the quickness and apparent irregularity of their development, are the immediate result of a combination of forces, the operations of which can neither be defined or foreseen. Jets and flame and wreaths of vapour start from the brilliant nucleus; while streaming away from the latter, in a direction opposite to the Sun, is a fan shaped tail, often traceable over a large span of the heavens and commingling its extreme fainter limits with the star dust in the background. p. 228

Author’s note:  Denning was all too aware of the unpredictability of comets, having observed them with great enthusiasm from his home in Bristol. Indeed, of all celestial objects viewed by amateurs it is arguably the comet which has the greatest ability to inspire or disappoint, even in the twenty-first century. And despite great strides in understanding comet morphology, astronomers can hardly ever reliably predict what kind of spectacle they will put on as they near the warming rays of the Sun. It was perhaps this unpredictability that so attracted Denning to these marvelous objects. Because of their rather elusive nature, at least at the end of the nineteenth century, discovering a comet was a sure way to come to the notoriety of one’s astronomical peers. Cash prizes and (more commonly) medals were issued by the astronomical societies of the world for the man or woman who would find a new comet. Indeed, a caricature of Mr. Denning was published in the April 9 1892 issue of Punch Magazine in honor of the discovery of his third comet (1892 II), which he stumbled across on the evening of Friday, March 18 1892. His discovery was also featured in The Times (Fig. 19.3). Denning informs us (bottom of p. 228) that some 300 comets had their orbits worked out at the time (1891), and a further 500 had been observed and deduces from this that they must be extremely plentiful. He then provides a general description of how a typical comet evolves as it moves closer to the Sun: Usually the telescope gives us the earliest intimation that one of these bodies is approaching us. It is first seen as a small round nebulosity, with probably a central condensation or stellar nucleus of the 10th or 11th magnitude. The whole object expands as its distance grows less, and it assumes an elongated form preparatory to the formation of a tail. The latter varies greatly in different instances; it may either be a narrow ray, as shown in the southern comet of January 1887, or fan shaped extension like that of the great comet of 1774. Barnard’s Comet of December 1886 exhibited a duple tail. Occasionally a fine comet bursts upon us suddenly, like that of 1843 or 1861.The former was sufficiently bright to be discovered when only 4 degrees from the Sun, and the latter presented itself quite unexpectedly as a magnificent object in the strong twilight of a June sky. p. 229

Although all the scientific facts were not in Denning’s possession, he does mention something of the physical nature of comets: Comets are not compact or coherent masses of matter; they more likely represent vast groups of planetary atoms, more or less loosely dispersed and sometimes forming streams. The effect of sunlight upon such assemblages will be that the whole mass becomes illuminated according to density, and that no phase will be apparent insomuch as the light is able to penetrate through its entirety. p. 230

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Fig. 19.3 William F. Denning of comet fame; a cartoon published in Punch magazine, Vol 102 April 9, 1892. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ William_Frederick_ Denning#/media/ File:William_Frederick_ Denning_-_Punch_ cartoon_-_Project_ Gutenberg_eText_14592. png)

Author’s note:  Denning’s assertion that comets are loose assemblages of matter proved to be correct! Cometary bodies are well described as ‘dirty snow balls’ with average densities about 50% that of water, and which typically contain water ice, dust, and an enrichment of simple organic molecules including hydrogen cyanide, methanol and formaldehyde. On p. 230 Denning provides us with details of how a comet’s orbit may be computed. If three trustworthy observations of the comet’s position have been made, it is possible to distinguish between the conic sections represented by the parabola, ellipse and hyperbola. Only comets that follow elliptical orbits, he informs us, are periodic. Thereafter Denning launches into a fascinating general discussion on a great many comets dating back to the sixteenth century. On p. 231 he mentions that it is his belief that Sir William Herschel may have mistakenly identified some comets as nebulae, as they were subsequently shown not to exist in the locations he noted for them. The chapter is generously illustrated with drawings of famous comets, many of which were seen and drawn by Denning himself. Comet seeking has more to do with the quality of the observer than the equipment he/ she employs. After all, as he reminds us, “Messier discovered all his comets using a small 2-foot telescope of 2 1/2 inches aperture magnifying 5 times and a field of 4°.” On p.  252 he gives more specific recommendations on the kind of instrument suited to comet sweeping: Opinions are divided as to the most suitable aperture and power for this work. Any telescope from 4 to 10 inches may be employed in it. A low power (30 to 50) and a large field (50 to 90′) eyepiece are imperative; and the instrument, to be really effective, should be

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mounted to facilitate sweeping either in a vertical or horizontal direction. A reflector on an altazimuth stand is a most convenient form for vertical sweeps. The defining capacity of the telescope need not necessarily be perfect to be thoroughly serviceable, the purpose being to distinguish faint nebulous bodies, and not details of form. Far more will depend upon the observer’s aptitude and persistency than upon his instrumental means, which ought to be regarded as a mere adjunct to his powers and not a controlling influence in success, for the latter lies in himself. Very large instruments are not often used, because of their necessarily restricted fields. Moreover, small instruments, apart from its advantage in this respect, is worked with greater flexibility and expedition. pp. 252–3

Author’s note:  Comet seeking by amateurs has greatly declined in recent years owing to the establishment of automated surveys using large, observatory -class telescopes, but it is still true that the majority of successful comet hunters in the last few decades employ moderate (generally less than 16 inches) aperture telescopes, capable of fairly wide fields of view, and low powers. A good example is the telescopes used and owned by the Canadian amateur astronomer and discoverer of 22 comets, David H. Levy. Some of Levy’s work will be covered later in the book. On pp. 252 through 253, Denning provides the reader with most invaluable data concerning the number of hours he and his astronomical contemporaries worked while comet hunting. He mentions this rather in passing, as the subsection really concerns the suitability of the English climate to the task of seeking comets: From some statistics printed in the ‘Science Observer,’ Boston, it appears that during the seven months from May to November, 1882, Lewis Swift was comet seeking during 300 hours. I have no English results of the same kind, but my meteoric observations will supply a means of comparison. From June to November, 1887 (six months), I was observing during 217 hours, and for nearly a similar period during the last half of 1877, though in each year work was only attempted with the Moon absent. My results for 1887 averages 36 hours per month, which is little less than the average derived from the comet seeking records above quoted. It is therefore fair to suppose that as much may be done here as in some regions of the United States. Mr. W.  R. Brooks wrote me in 1889, saying, “We have much cloudy weather in this part of America. While in other portions of the country clear weather abounds, it is not so in this section, where much of my work has been done. This is a most fertile section; the beautiful lake region of N.Y.; but it is for this reason a cloudy belt. It is far different in Colorado and California. In the latter place, at Lick Observatory, I hear they have 300 clear nights a year; a paradise for the astronomical observer. pp. 251–2

Yet, then as now, the keen telescopist may have to contend with prolonged periods of cloudy weather. In a letter he received from Professor Swift dated July 30, 1889, he says: “I arrived home, after a few weeks’ visit to the Lick Observatory, on March 1, and have not had half a dozen first class nights since; not in thirty years have I seen such prolonged rainy and cloudy weather.” p. 252. Author’s note:  This provides solid evidence of the both the industry of these Victorian observers and the likely frequency of opportunities available to observe. Factoring in the many other nights when Denning was actively observing while the Moon was in the sky, it is not unreasonable to think that the British climate is much more amenable to pursuing our wonderful hobby than is commonly believed! On p. 255, Denning presents more historical data showing the average annual rate of discovery of cometary bodies from 1782 through to 1889. Prior to 1845,

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between 1 and 2 comets were discovered per year, but after 1845 it increased several fold, so that by the 1880s it had increased to about 5 per year. This undoubtedly reflects the increasing number of astronomers joining the race to uncover them. In addition, he presents data illustrating at what times of the year these comets were discovered. During the months of July and August, the number of comets discovered peaked but was generally higher in the second half of the year. Denning does not provide an explanation, but it seems reasonably clear that the longer periods of twilight during the summer months afford greater opportunities for observers to pick up comets approaching the Sun. In addition, the second half of the year is warmer in the northern hemisphere (where virtually all comets described by Denning were discovered) making comet sweeps more pleasurable. Author’s note:  What invaluable information we have here!

Chapter XV: Meteors and Meteoric Observations Covering Pages 260–285 No one can contemplate the firmament for long on a clear moonless night without noticing one or more of those luminous objects called shooting stars. They are particularly numerous in the autumnal months, and will sometimes attract special attention either by their frequency of apparition or by their excessive brilliancy in individual cases. For many ages little was known of these bodies, though some of the ancient philosophers appear to have formed correct ideas as to their astronomical nature. Humboldt says Diogenes of Apollonia who probably belonged to the period intermediate between Anaxagoras and Democritus, expressed the opinion that, “together with the visible stars, there are invisible ones which are therefore without names. These sometimes fall upon the Earth and are extinguished, as took place with the star of stone which fell at Aegos Potamoi.” Plutarch, in the “Life of Lysander,” remarks: “Falling stars are not emanations or rejected portions thrown off from the ethereal fire, which when they come into our atmosphere are extinguished after being kindled; they are, rather, celestial bodies which, having once had an impetus of revolution, fall or are cast down to the Earth, and are precipitated, not only on inhabited countries, but also, and in greater numbers, beyond these into the great sea, so that they remain concealed.” In later times however, opinions became less rational. Falling stars were considered to be of a purely terrestrial nature, and originated by exhalations in the upper regions of the air…. Another theory, attributed to Laplace, Arago, and others, was that meteors were ejections from lunar volcanoes. But these explanations were not altogether satisfactory in their application. The truth is, that men had commenced to theorize before they had begun to observe and accumulate facts. They had learned little or nothing as to the numbers, directions, and appearances of meteors, and therefore, possessed no materials on which to found any plausible hypothesis to account for them. pp. 260–61

Denning was the ultimate outdoor man, preferring, if at all possible, to be under a starry sky than being huddled up indoors. He was the consummate observer, being equally adept both with and without a telescope. Indeed, as this author has alluded to earlier, he probably spent more observing time with his naked eye than peering through the eyepiece of his permanently stationed reflecting telescope. Denning was

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an international authority on meteors. Indeed, it was his research in this area of observational astronomy that led to his election as fellow of the Royal Astronomical Society. That said, it was the reaction to his ideas (and exacerbated by a midlife illness) concerning these luminous bodies that ultimately led to his withdrawal from public life. Once again, Mr. Denning opens this chapter with exquisite prose, extolling the knowledge of the ancients who pondered the nature of the ‘shooting stars’ just as solemnly as we do today. Indeed, he reminds us that many ideas that we receive as ‘modern’ or ‘contemporary’ often had their originations in the ruminations of minds that have long since departed this world. What is more, the march of time is no guarantee that ideas become any more developed than they were when they were first conceived of in the backwater of human history. All of human thought is to be likened to the winding course of a meandering river and, more often than not, intellectual brilliance is no safeguard against being dead wrong. While many observers throughout history were keen to report the brightness and color of meteors, few had the presence of mind to record the direction and longevity of such events. It is these latter facts, Denning explains, that were of greater importance in elucidating their true nature. He continues to ascribe credit where it was due to a number of pioneers in this field including Edward Heis (1806–77), who conducted a systematic study of meteors, including their trajectories on the celestial sphere. He also acknowledges the work of the German astronomer, Julius Schmidt (1825–1884), based at Bonn and Athens, and contributions from his compatriots, Professor Alexander Herschel (1836–1907), grandson of Sir William Herschel, and Mr. R.  P. Greg, who collated and analyzed large bodies of observational data to calculate the all-important radiant points; loci on the celestial sphere through which meteors were seen to emanate. By the 1850s it was becoming clear that meteor showers were strongly associated with comets, but it was the Italian astronomer, G. V. Schiaparelli, who in 1866 definitively associated them with the orbits of comets. Analyzing the Perseid meteor shower, Schiaparelli provided incontrovertible evidence that they were associated with the orbit of Comet III 1862. He also showed that the meteor showers of November were also strongly correlated with the orbit of Comet Temple 1861 (page 264). Meteor showers, it became clear, occur when Earth swept up debris from the tails of comets as it intersected their orbits in space. Thereafter, Denning engages in a brief but fascinating discussion of meteorites that had fallen to earth without being completely destroyed. On page 266, he lists a number of historical meteorite finds dating back to 1478 b. c. through to the end of the nineteenth century. On p. 267, he notes that these meteorites fall into a variety of categories: those in which iron was found to constitute their bulk (siderites), those of mixed stone and metallic composition; siderolites; and those entirely composed of rocky material, aerolites. Author’s note:  While the nomenclature of meteorites has changed in modern times, the basic classification system employed by Denning still stands today. The vast majority of these are classified as chondrites, and are composed of a variety of

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silicate minerals and small amounts of organic matter, arranged in roughly spherical particles called chondrules. About 8% are achrondrites, characterized by their more amorphous nature and resemblance to terrestrial igneous rock. The remainder have substantial metal content (stony irons or iron meteorites). From pp. 267 through 270, Denning relates some fascinating firsthand accounts of fireballs, unusually bright, violent, and long lived meteors, including a few of his own description, that occurred throughout the nineteenth century. Some of these were real monsters. For example, in the table presented on p. 268 of his book, he relates that one fireball witnessed by a one G. von Niessl, began to incandesce about 250 miles above the ground and fell to an altitude of 85 miles before disappearing. In so doing, it crossed a whopping 1200 miles of sky! Denning includes an eyewitness testimony of a meteorite which fell in Mazapil, Mexico, on the evening of November 27, 1885 (see p. 270). And in another account, he relates the sonic boom associated with a fireball which streaked across the sky on the evening of November 23, 1877, in which “the explosion of a 13-inch bombshell, consisting of 200 pounds of iron, would not have produced a sound of one hundredth part the intensity of the meteor explosion.” It is clear from these communications that Denning had a very special interest in the human dimension of meteor science; when earth and sky converge to break the monotony of an otherwise ordinary day. Author’s note:  While this author has enjoyed some memorable fireballs over the years, some notable apparitions were entirely missed. Perhaps the most memorable ‘non event’ occurred in the early evening of Monday, February 29, 2016, when an unusually loud and bright green fireball streaked across the skies of Scotland and northern England, creating quite a media sensation. A telescope had already been set up in the author’s back garden for the purposes of conducting some routine double star observations, when he retired indoors to ‘spend a penny.’ A few minutes later, he heard his cell phone ‘ping’ as a few excited friends texted him inquiring if he had seen the fireball streaking across the sky. “No,” he replied, “I was on the throne!” On pp. 271 through 272, Denning describes some extraordinary meteor storms that occurred in history, most notably on November 12, 1799, and one in the wee small hours of November 13, 1833, when the people of North America counted more than 1000 meteors per minute over the space of 2 h! Another storm apparently occurred on November 27,1872, “when 33,000 meteors were counted by Denza and his assistants at Moncalieri, Italy, between the hours of 5 h 50 m and 10 h 30 m P.M.” Author’s note:  Such reports have become the stuff of legend in modern times, with all meteor showers in recent years being more of a disappointment than anything else. It’s almost as if some events in the heavens are winding down?! Or maybe we just need a peppering of new comets! On pp. 272 through 273, Denning launches into a fascinating discussion on the subject of telescopic meteors (see the curious drawing by W.  R. Brooks, repro-

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duced in Fig.  57), that is, meteors seen moving across the field of view of the telescopic field: Observers engaged in seeking for comets or studying variable stars employ low powers and large fields, and during the progress of their work notice a considerable number of small meteors. At some periods these bodies are more plentiful than at others, and appear in such rapid succession that the observer’s attention is distracted from the special work he is pursuing to watch them more narrowly and record their numbers. They range between the 7th and 11th mags. Winnecke in the year 1884 noticed 105 of these objects on thirty two evenings of observation with a 3 inch finder, power 15, and field of 3 degrees. I have also remarked many of these objects when using the comet eyepieces of my 10 inch reflector and find they are apparently more numerous than the ordinary naked eye meteors in the proportion 22 to 1. It would be supposed from the great rapidity with which the latter shoot across the firmament that the smaller telescopic meteors are scarcely distinguishable by their motion, as they dart through the field instantaneously and only be perceptible as lines of light. But this impression is altogether inconsistent with the appearances observed. They possess no such velocity, but usually move with extreme slowness, and not unfrequently the whole of the path is comprised within the same field of view. The eye is enabled to follow them as they leisurely traverse their courses, and to note peculiarities of aspect. Of course, there are considerable differences of speed observed, but as a rule the rate is decidely slow and far less than that shown by naked eye meteors. I believe that telescopic meteors are situated at great heights in the atmosphere, and that their diminutive size and slowness of movement are due to their remoteness. pp. 272–3

Author’s note:  Granted, any reasonably experienced observer has seen meteors streak across the field of view of his/her telescope, but who among you would take the time to measure the ratio of naked eye meteors in comparison to those seen at the telescope? Personally, this author has never taken the time to even consider such a question, though he concedes that the description of the various speeds of telescopic meteors is accurate from his own experiences in the field. Denning offers us a good explanation as to why some appear to move relatively slowly across the field of view; they are located at greater altitudes. What remarkable insight! What a wonderful pastime this could become for someone with modest equipment! On pp.  274 through 276, Denning provides brief overviews of all the major meteor showers enjoyed in the northern hemisphere throughout the year. On page 277 we gain a glimpse of the sheer enthusiasm he had for observing such phenomena. Figure 58 shows a curious drawing of the changing appearance of a slow moving meteor as it made its way across the sky during the early evening of December 28 1888. He noted its change in brightness at various intervals as well as its morphology and committed the apparition to memory! The remaining pages of the chapter describe the details of finding meteor radiants and the question of whether these points are stationary or whether they in fact move. We now understand that meteor radiant points are not stationary but are seen to slowly drift eastward by about a degree per day on average. Denning disputed this conclusion.

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Chapter XVI: The Stars Covering Pages 286–323 The planetary observer has to accept such opportunities as are given him; he must use his telescope at the particular seasons when his objects are well presented. These are limited in number, and months may pass without one of them coming under favourable review. In stellar work no such irregularities can affect the progress of observations. The student of sidereal astronomy has a vast field to explore, and a diversity of objects of infinite extent. They are so various in their lustre, in their grouping, and in their colours, that the o­ bserver’s interest is actively retained in his work, and we often find him pursuing it with unflagging diligence through many years. No doubt there would be many others employing their energies in this field of labour but for the uninteresting character of star disks, which are mere points of light, and therefore incapable of displaying any detail. Those who study the Sun, Moon or planets have a large amount of surface configuration to examine and delineate, and this is ever undergoing real or apparent changes. But this is wholly wanting in the telescopic images of stars, which exhibit a sameness and lack of detail that is not satisfying to the tastes of every observer. True there are some beautiful contrasts of colour and many striking differences in magnitude in double stars; there are also the varying position and distance of binary systems, the curious and mysterious fluctuations in variable stars, and some other peculiarities of stellar phenomena which must, and ever will, attract all the attention that such important and pleasing features deserve. And these, it must be conceded, form adequate compensation for any other shortcomings. The observer who is led to study the stars by comparisons of colour and magnitude or measures of position, will not only find ample materials for a lifelong research, but will meet with many objects affording him special entertainment. And his work, if rightly directed and accurately performed, will certainly add something to our knowledge of a branch in which he will certainly find such delectation. pp. 286–7

As was explained previously, W.  F. Denning was arguably the last master of observational astronomy. Many of his contemporaries were already specialists, knowing much about one area of astronomy but having relatively little practical knowledge of other areas. Not only were his contributions to astronomical knowledge confined to the shallows of the Solar System, they extended far beyond the empire of the Sun, to include the distant stars and nebulae. Indeed, during his routine comet sweeps he was one of the first to observe Nova Aquilae on June 8, 1918, and just over two years later, he discovered Nova Cygni 1920. Further afield, his keen eye uncovered two score new nebulae never before seen. Indeed, if there were anyone who could convey the joyous enthusiasm of observing the stellar heaven, it would be Denning. It is in this outward-bound spirit of exploration that we shall continue to study the knowledge of this extraordinary human being. In the opening pages of this chapter, Denning sets out the basic route by which the keen amateur might secure knowledge of the starry heaven. Familiarity with the Greek alphabet is, of course, essential to understanding how the stars within the various constellations are presented. In general (but not always), the brightest luminary is designated alpha, the second most, beta, and so on. Denning suggests that the basic outlines of the classical constellations be memorized (p. 290). While he acknowledges that the star patterns often do not resemble the classical figures very strongly they are useful because they conveniently divide up the celestial

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sphere, “giving each a distinguishing appellation, so that it might be conveniently referred to.” Interestingly, Denning warns against trying to change this traditional system of parsing the visible night sky: There are some who object to the method of the Chaldean shepherds because the series of grotesque figures on our star maps and globes bear no natural analogies. But it would be unwise to attempt an innovation in what has been handed down from the myths of a remote antiquity for; “Time doth consecrate, And what is grey with age, becomes religion.” p. 290

Author’s note:  How prescient of Denning to raise this issue! This author vividly remembers a telescope forum thread entitled “Unlearning the Constellations,” raising this very issue. What arrogance to think that any such move would yield anything worthwhile! How disrespectful it is to dishonor the traditions of every generation since the dawn of civilization! On whose authority did you write? Your own? Needless to say, the same proposal, like all other historical attempts, fell flat on its face. Mr. Denning continues this chapter by discussing the (then) popular activity of double star observing and mensuration, emphasizing the use of the filar micrometer as a tool that could be exquisitely mated to the telescope. He then discusses the kinds of instruments that are suitable to such an activity, rightly acknowledging the traditional role of the classical refractor as highly favored but also admitting that the reflecting telescope is almost as good: ….it is notable that refracting telescopes have accomplished nearly the whole of the work. But reflectors are little less capable, though their powers seem to have been rarely employed in this field. Mr. Tarrant has lately secured a large number of accurate measures with a 10 inch reflector by Calver, and if care is taken to secure correct adjustment of the mirrors, there is no reason why this form of instrument should not be nearly as effective as its rival. Mr. Tarrant advises those who use reflectors in observing double stars, “to test the centring of the flat at intervals during the observations, as the slightest shift of the large mirror in its cell will frequently occasion a spurious image which, if it by chance happens to fall where the companion is expected to be seen, will often lead to the conclusion that it has been observed. In addition, any wings or the slightest flare around a bright star will generally completely obliterate every trace of the companion, especially if close and of small magnitude, and such defects will in nine cases out of ten, be found to be be due to defective adjustment. Undoubtedly, for very close unequal pairs the refractor possesses great advantages over a reflector of equal aperture; in the case of close double stars the components of which are nearly equal there appears to be little, if any, difference between the two classes of instruments; while for any detail connected with the colour of stars the reflector comes to the fore from its being perfectly achromatic.” These remarks from a practical man will go far to negative the disparaging statements sometimes made with regard to reflectors and stellar work, and ought to encourage other amateurs possessing these instruments to take up this branch in a systematic way. pp. 290–2

Author’s note:  Having extensively tested classical and contemporary apochromatic refractors, catadioptric and Newtonian telescopes on a suite of double stars,

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this author reached the following conclusions, which are in complete agreement with the findings of Mr. Denning and Mr. Tarrant: Apochromatic refractors are no better than a good traditional achromat of decent focal ratio in splitting doubles. This is amply borne out in historical studies, as this book reveals. Catadioptrics make excellent, high resolution double star telescopes. Millimeter for millimeter, refractors are better than Newtonians at resolving the tightest, unequal pairs, but the differences are largely eliminated by employing a Newtonian of slightly larger aperture, provided the prevailing seeing conditions allow. In general, the optical quality of a telescope is far less important than the prevailing sky conditions, as well as the skills the would-be observer brings to the table. This author’s 8 inch f/6 reflector was found to be noticeably superior to a first rate 5″ f/12 at divining close doubles of either unequal or equal magnitudes, the generous gain in aperture completely negating any advantages incurred by using a smaller, unobstructed aperture. These results fly in the face of self-promoted ‘authorities’ who have zealously defended the refractor as the only choice for such work. To continue to do so is downright dishonest and actually completely misleading to those who wish to explore this branch of visual astronomy. Thankfully many more amateurs have been made aware of this and are testing out a variety of telescopes in the pursuit of tricky double stars. The reader will also be interested to know that in many cases the results were obtained using telescopes with a sub-f/5 focal ratios. Denning’s remarks concerning the superior color fidelity of reflecting telescopes (in this case, the silver on glass variety) are also wholly valid. Despite the wonderful pantheon of adjectives coined to describe the color of stars in refractors, none enjoy the perfect achromaticity of the reflector, a point fully appreciated by Denning. Concerning the theoretical separation of members of a binary star system, Denning appeals to the work of the Reverend William Rutter Dawes, who offered his famous formula for splitting doubles of equal brilliance (actually magnitude 6), which asserts that the tightest double star that can be resolved with a given instrument is approximated by 4.56″/ D where D is the aperture in inches. He provides a convenient table of theoretical separations on page 292 for the interested reader. On page 293, Denning offers the additional findings of the optician, a one Mr. Dallmeyer, who provided this result which agrees well with Dawes’ findings: “In all calculations I have made, I find that 4.33 divided by the aperture gives the separating power.” p. 293. Denning, being intimately familiar with the behavior of large and small apertures, offers this cautionary note: A large aperture will sometimes fail to reveal a difficult and close comes to a bright star when a smaller aperture will succeed. This is due to the position of the bright diffraction ring, which in a large instrument may overlap the faint companion and obscure it, while in a small one, the ring lies outside and the small star is visible. p. 293

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Although many amateurs continue to erroneously conflate the ability of a telescope to split a given pair with its optical quality, Denning prefers to lean on the wisdom of his learned predecessor: “Dawes concluded that; “tests of separation of double stars are not tests of excellence of figure.” p. 293. In a curious footnote provided at the bottom of p. 293, we learn more of measurements made at the telescope regarding the position of the first diffraction ring: Mr. George Knott, of Cuckfield, mentions that the radius of the first bright diffraction ring of a stellar image, for a 7.3 inch aperture is 1.01″, and for one of 2 inches 3.7″. Mr. Dawes is quoted as giving 1.25″ for a 7 inch, 1.61″ for a 5.5 inch and 3.57″ for a 2.4 inch. These figures exceed the theoretical values, if the latter are adopted from Sir G.B.  Airy’s “Undulatory Theory of Optics”, where for mean rays we have; Radius of object glass in inches x radius of bright ring in seconds = 3.7. p. 293

Author’s note:  In independent work, this author derived the formula 185/D where D is expressed in millimeters represents the locus of the first diffraction ring. Converting to millimeters and plugging the numbers above into this equation gives the radius of the first diffraction ring for a 7.3 inch and 2 inch aperture respectively as:

185 / 185 = 1′′and185 / 50 = 3.7″

These figures, which are derived from Airy’s theoretical work, show that they are in perfect (perhaps too perfect?) agreement with Knott’s measurement. Dawes’ results for the 7-, 5.5- and 2.4-inch apertures are, respectively:

185 / 178 = 1.04″ ,185 / 139.7 = 1.32″ , and185 / 60 = 3.08″

which are indeed lower than those predicted in theory. The latter values are still quite close to those derived in Airy’s theory, and like any measured value, they may be subject to some systematic error. Given the wiggle room for error, this author wonders whether Dawes’ findings are more reliable than those produced by Knott? Alas, we shall never know for sure, but it remains a fascinating topic of discussion nonetheless. The next section of the chapter diverges considerably from the previous in discussing the number of stars of varying glory in the firmament. When this author was a boy, he learned from various books that about 3000 are visible to the naked eye from a clear, dark sky, though Denning offers a figure of approximately 5000 (p. 293). Of course, the number will vary according to the kind of sky one encounters as well the keenness of one’s visual system. Denning’s own estimate may also reflect the darker skies he enjoyed, writing as he did in the late Victorian era. With every increase in magnitude, there is a great increase in number, but there is no fixed power law that might enable us to compute how many more stars there might be as the magnitude is increased. Argelander estimates that each magnitude exhibits a rise of about 300%. Indeed, in data presented on p. 294, he provides these

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figures, collated from a survey between 2° south of the equator all the way to the North Pole: 1st: 20 2nd: 65 3rd: 190 4th: 425 5th: 1100 6th: 3200 7th: 13,000 As one can see, the threefold increase per magnitude is only very approximate, but nonetheless it is a useful result. Of course, without the unblinking eye of a photometer, a legitimate question arises; how does one estimate stellar magnitudes accurately? Denning discusses this on pp. 294 through 295, where he presents magnitude estimates made by Sir John Herschel and Struve (he doesn’t mention which one). Interestingly, for the stars between magnitude 4 and 6, the discrepancy amounts to about 0.5 stellar magnitudes, but as the stars become fainter (down to magnitude 14 or so), the discrepancies become larger. This is entirely understandable, as fainter stars will be more difficult to estimate. Intriguingly, Denning was also cognizant of two newly-minted photometric surveys conducted at Harvard College and Oxford University Observatories, which showed much better agreement with each other, with 31% of the stars monitored differing by 0.1 magnitude, 71% differing only by 0.25 stellar magnitudes and 95% of all stars surveyed showing no greater than 0.33 stellar magnitude difference. Reading from the summary of that comparative survey, he notes, “a great step has been accomplished towards an accurate knowledge of the relative lustre of the stars.” p. 295. Author’s note:  Denning lived during the rise of astrophysical science, where the eye was rapidly being replaced by instruments that were considerably more sensitive than the human eye. It is unclear as to how he felt about this new era dawning on the world, but he gives this author no reason to suppose that he did not embrace it. After all, Denning was ostensibly a truth seeker in everything he did. On pp. 295 through 297, Denning describes the visual appearance of the Milky Way, both to the naked eye but also through the telescope. He describes the profusion of stars which vary both in number, grouping, brilliance and variation of hue, as the telescope is moved from one field to another. But some regions of the Milky Way are conspicuous by their absence of stars and accordingly he mentions the Coalsack and various dark, cavernous regions running through Scorpius and Sagittarius which offer “striking contrast to the silvery sheen of surrounding stars.” (p. 296) Such regions were marveled at, and studied to great effect, by his distinguished American contemporary, E. E. Barnard. Author’s note:  Sweeping the Milky Way on a dark, moonless night with a large telescope remains a great joy for this author. With a modern, low power, wide angle ocular, a field in excess of 2° is possible. He imagines Denning using his favorite

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comet seeking eyepiece, delivering a power of about 32 diameters in a field fully 1.25° wide (see p.  254 for details of his equipment) for the express purpose of exploring the vast reaches of the Milky Way. The activity never ceases to amaze, especially when one contemplates the reality of what the eye presents. The effects of stellar scintillation are described on pp.  297 through 298. He informs us that it was Sir Robert Hooke, who in 1667 provided the explanation for this charming natural phenomenon, which he attributed to “irregular refractions of the light of the stars by differently heated layers in the atmosphere.” Denning also clearly understood why planets, in comparison to stars, do not exhibit much in the way of scintillation: “The planets,” he writes, “are little subject to scintillation as they present disks of sensible size, and thus are enabled to neutralize the effect of atmospheric interferences.” p. 297. Curiously, he points out that while higher altitude sites, where many observatories were being established, present thinner air which generally increases the steadiness of the images garnered at the telescope, there were, even then, exceptions to this rule: In February 1888, Dr. Pertner, of the Vienna Academy of Sciences, found “that scintillation of Sirius was actually greater at the top of Sonnblick, 10,000 feet high, than it was by the base of the mountain, and he formed the opinion that scintillation has its origin in the upper strata of the atmosphere and not in the lower as usually assumed.” It would appear from this that lofty situations do not possess all the advantages claimed for them in regard to the employment of large telescopes. p. 298

Author’s note:  This author possesses firsthand experience of this. At a site located 8500 feet up in the White Mountains of Eastern California, the seeing was often (but not always) more turbulent than it was in his own backyard at sea level! A mere 10  years before Denning was born, astronomers of the ilk of Bessel, Struve and Henderson had painstakingly obtained the first stellar parallaxes that enabled them to measure the vast distances to the nearby stars. On p. 299, he reports on the progress that had been made in his own lifetime, including (revised) estimates for 61 Cygni, but also for Alpha Crucis and Vega (alpha Lyrae). The parallaxes obtained (just fractions of a second of arc), established their distances with fairly good accuracy. Vega, for example, is quoted as having an annual parallax of 0.15″ corresponding to a distance of 22 light years. The modern value places this system a little farther away, at 25 light years. Regardless of the errors still at large in these early data, Denning was fully cognizant of the mind boggling separations between the stars! Author’s note:  Though we have known the colossal distances between the stars for the best part of two centuries, it never ceases to impress this author how much these facts have a bearing on what one sees and contemplates at the eyepiece. Facts have consequences. Seeing is a time machine; the telescope a wondrous tool that empowers humanity with the ability to actively see the past, both recent and remote. On p. 300, Mr. Denning resumes his discussion of individual double and multiple stars. Ever mindful of the experience level of his readership, he provides excellent

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visual descriptions of the most comely stellar systems that require only modest telescopic aid to fully enjoy. These include, Polaris, Rigel, Antares, Sirius (which he fully admits is exceedingly difficult from anywhere in England owing to its very low altitude). Figure 62 presents what are presumably his own artistic renderings of a suite of favorites including, Gamma Leonis/ Arietis/ Andromedae and Virginis, Delta Cygni and Serpentis. All of these systems would have been easy targets for his 10 inch With Browning reflector and indeed can be just as easily savored by an observer equipped with a small refractor of say three or four inch aperture. On pp. 302 through 305, Denning presents a comprehensive table of double stars of increasing difficulty, starting with sub- arc second pairs and extending through to systems that are within easy reach of ordinary binoculars or field glasses. In this table, their measures are presented together with some notes supplied by the astronomer who conducted these measures. These include contributions from Burnham, Tarrant, Schiaparelli, Leavenworth, Engelmann, Perottin, Struve II and Maw. The reader will be made aware of several sub- arc second measures made by Tarrant, who, as we have previously learned, employed a 10-inch Calver reflector. Tarrant’s tightest system is Lambda Cassiopieae (dated 1887.3), the components of which are both magnitude 6.5 and, at the time of writing, separated by a mere 0.45 s of arc! Author’s note:  How wonderful and important historical books can be in establishing universal truths in visual astronomy! For the record, this author has split several sub- arc second pairs with his 8 inch f/6 Newtonian reflector from his backyard. In a curious note at the bottom of p. 301 and carried over to p. 306, Denning mentions something of interest: Certain doubles such as theta Aurigae, delta Cygni and Zeta Herculis are more easily seen in twilight than on a dark sky; and some experienced observers, conscious of this advantage, have observed excellent measures in daylight. Mr. Gedhill says: “such stars as gamma Leonis and gamma Virginis, are best measured before or soon after sunset.” pp. 301–306

Author’s note:  Living in a country where strong twilight exists from May through to late July, and with little else to see in the sky at the time, this author has become especially adept at viewing double stars in incomplete darkness and can fully vouch for Denning’s assertion as well as Gedhill’s endorsement. Many an evening can be passed examining the beautiful, calm images of Eta 1 & 2 Lyrae, Iota Cassopieae, Epsilon, kappa, Pi and Xi Bootis, as well as Alula Borealis & Australis, using small instruments from the comfort of his back garden. Sunset and twilight conditions are indeed excellent times to catch these stellar systems. Indeed, more than half the fun is finding them in a less than dark sky! More so than in others, Denning darts about a bit in this, the penultimate chapter of the book, discussing variable stars before returning once again to multiple star systems. Arguably the most interesting is the Theta Orionis system; affectionately known as the Trapezium, owing to its strong resemblance to this geometric form. The stellar quartet is, of course, visible in all but the smallest instruments but is the

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reader aware of when the other, fainter components of this fascinating cluster of neonatal stars were first observed? Denning provides us with the answer, and then some; In 1826 Struve discovered a fifth star, and in 1830 Sir John Herschel found a sixth; these were both situated a little outside the trapezium. All these stars have been seen in a 3 inch telescope. The great 36 inch equatorial at Mount Hamilton has added several others; one was detected by Alvan G. Clark (the maker of the object glass) and another by Barnard. These were excessively minute and placed within the trapezium. Barnard has glimpsed an extremely minute double star exterior to the trapezium and forming a triangle with the stars A and C…. The fifth and sixth stars have been supposed to be variable, and not without reason; possibly the others are equally likely to change, but this is only conjecture. Sir John Herschel says that to perceive the fifth and sixth stars” is one of the severest tests that can be applied to a telescope:” yet Burnham saw them both readily in a 6 inch a few minutes before sunrise on Mount Hamilton in September 1879. pp. 319–20

Author’s note:  The 5th and 6th stars of the Trapezium can often prove elusive but are more a test of local seeing conditions than raw visual acuity. This author has seen them many times in his career, but perhaps the most memorable was through a beautiful 4 inch f/15 classical achromat in ambient air temperatures of minus 11°C; conditions that he has seldom enjoyed since. That night the air was rock stable, as if he were viewing the cosmos through a finely polished precious gemstone. Denning mentions the complementary visions of two legendary observers; E.  E. Barnard, who had incredibly sensitive eyes capable of picking up objects on the precipice of what is humanly possible, and the eagle eyes of S. W. Burnham, who brought the international double star community to its knees in discovering hundreds of new doubles with a fine 6 inch f/15 Clark refractor where others, using instruments of far grander estate, reported nothing out of the ordinary. The variable star and nova enthusiast will find much that is of interest in this chapter, both scientifically and historically, on pages 309 through 316, with a neat table of the main variable stars being presented on page 311. On pp.  315–316, Denning brings up a perennial favorite amongst arm chair astronomers; the curious case of Sirius’ allegedly red color in antiquity: “Cicero, Seneca, Ptolemy and others speak of Sirius as a red star, whereas now it is an intense white; and if we rely on ancient descriptions similar changes appear to have affected other prominent stars. But the old records cannot be implicitly trusted, owing to errors of transcriber and translators; and Mr. Lynn (‘Observatory’ vol ix p.  104) quotes facts tending to disprove that Sirius was formerly a red star.” pp. 315–6. At the bottom of p. 316, Denning embarks on a discussion of groupings of stars, what we today call star clusters. He states that the average eye can make out 6 members of the Pleiades and a seventh, though more elusive, “is occasionally remarked.” Denning claims that in 1877 he “distinctly made out 14 stars in this group.” That’s quite a feat of visual acuity and perhaps an indicator of darker, clearer skies in the late Victorian period than of late. His telescope revealed Tempel’s nebula enveloping Merope, a not so trivial visual target in the early twenty-first century, even with a moderately sized instrument.

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Denning also provides some brief notes on some of the more celebrated star groupings including Praesepe in Cancer, a delightful sight in small telescope, Coma Berenices and a most wonderful description of Chi Persei, known to us today as the Double Cluster (Caldwell 14): Perceptible to the eye as a patch of hazy material lying between the constellations of Cassiopeia and Persei. In the telescope it calls a double cluster, and is one of the richest and beautiful objects that the sky affords. The tyro who first beholds it is astonished at the marvellous profusion of stars. It can be fairly well seen in a good field glass, but its chief beauties only come out in a telescope, and the larger the aperture the more striking they will appear. It is on groups of this character that the advantage of large instruments is fully realized. The power should be very low, so that the whole of the two clusters may be seen in the field. An eyepiece of 40, field 65′, on my 10 inch reflector, presents this object in its most imposing form. pp. 317–8

Author’s note:  From August right through to early spring, one of the objects this author visits routinely, even religiously, on every clear evening when the Moon is out of the sky is the Double Cluster. This author simply never tires of beholding the majesty of this stately grouping of stars; coruscating jewels of diamond, sapphire, topaz and ruby, assault the eye, inducing feelings of pure, unadulterated joy. Small wonder it is the stuff of poetry!

Chapter XVII: Nebulae and Star Clusters Covering Pages 324–46 These objects, though classed together in catalogs, offer some great distinctions which the observer will not be long in recognizing. It was thought at one period that all nebulae were resolvable into stars, and that their nebulous aspect was merely due to the confused light of remote star clusters. But modern telescopes, backed up by the unequivocal testimony of the spectroscope, has shown that nebulous matter really exists in space. The largest instruments cannot resolve it into stars, and it yields a gaseous spectrum. The conjecture has been thrown out that it may be considered as the unformed material of which suns and planets are made. p. 324

William Denning penned his great treatise on visual astronomy at the crossroads between new and old worlds. Advances in astronomy were revealing a cosmos far grander and more complex than anyone had dared to imagine just a few decades before. Spectroscopy, photography and the rise of giant telescopes provided new ways of reading the ‘book of nature’. Yet all the while, Denning kept on doing what he did best; quietly going about his solitary vigils of the heavens, his simple telescope ever ready to carry him to distant worlds. In this, the final chapter of the book, he presents a distillation of what was known about the most distant objects in the heavens, the mysterious nebulae, star clusters and ‘Island Universes’ and how the ordinary man could engage in a systematic study of these magnificent objects. Denning opens this interesting chapter by setting forth a summary of the progress made in discovering and classifying the various nebulae; gaseous, elliptical and

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spiral, as well the various open and globular star clusters characterized at the time of writing. Such was the rate of discovery of new nebulae that D’Arrest considered the real possibility that their number would turn out to be “infinite.” A new edition of Sir John Herschel’s catalog of deep sky objects had been published by the Royal Astronomical Society in 1888, listing some 7840 items, and which collated the works of the great pioneers in this arena of observational astronomy, including the Herschels, Lord Rosse, D’Arrest, Marth, Tempel, Stephan and Swift. The success of these astronomers, Denning points out, was largely due to the employment of larger aperture telescopes that could collect more light to bring fainter and fainter objects into view. What’s more, only with large telescopes could any real structure be delineated within many of these objects. Concerning celebrated targets such as the Whirlpool Galaxy, the Dumbbell, Horsehoe and Crab Nebula, for example, he states: “An instrument of smaller diameter is quite inadequate to deal with them. They can be seen, it is true, and the general shape recognized in the most conspicuous examples, but their details of structure are reserved for the greater capacity of larger apertures.” p. 325. Ever fond of quoting statistics, Denning informs us that the distribution of nebulae is far from uniform, at least in the northern hemisphere, being highly concentrated toward the constellations of Leo, Coma Berenices and Virgo, but much more sparsely toward Perseus, Taurus and Auriga, for example. Curiously, because of a lack of knowledge concerning the nature and distance of many of the nebulae, some astronomers formed the opinion that they underwent changes in form and even position! Denning himself is inclined to agree in principle: “It is in the highest degree probable that changes occur in the visible appearance of certain nebulae, though the opinion is not perhaps supported by a sufficient number of instances.” p. 327. Indeed, he presents a series of curious historical accounts of alleged “variable nebulae” phenomena in pp.  327 through 330, which the reader may find interesting. When it comes to nebulae, there appears to be a great range of acuities among astronomers as to what is and is not actually seen. Consider the intriguing story of the Merope Nebula recounted by Denning on pp. 329 and 330: On Oct. 19, 1859, Tempel discovered a faint, large nebula attached to the star Merope, one of the Pleiades, and at first mistook it for a diffused comet…. An impression soon gained ground that this object was variable; for while Schmidt, Chacornac, Peters, and others saw it with small instruments, it could not be discerned by D’Arrest and Schjellerup with the large refractor at Copenhagen. Swift saw the nebula easily in 1874 with a 4.5 inch refractor, and has observed it with the aperture contracted to 2 inches. Backhouse reobserved it in 1882 with a 4.5 inch refractor. Yet in March 1881 Hough and Burnham sent a paper to the Royal Astronomical Society with an endeavour to prove that the nebula did not exist! They had frequently searched for it during the preceding winter, but not a vestige of the object could be seen in the 18.5 inch refractor at Chicago, and they regarded the supposed nebula as due to the glow proceeding from Merope and neighbouring stars. But photography has entirely refuted this negative evidence, and has shown, not only Tempel’s nebula, but others involving the stars Maia, Alcyone, and Electra, belonging to this cluster. pp. 329–30

Author’s note:  What a remarkable story! The reader will recall how Burnham (discussed in a later chapter), arguably the most keen-eyed double star observer in

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history, couldn’t see the Merope Nebula even with such a large telescope! It would indeed appear to be the case that the ability to perceive faint objects is not at all related to the eye’s ability to resolve details. Some folk will be better deep sky observers than others! Perhaps the episode might have been entirely avoided had E. E. Barnard been assigned to the project instead of Burnham! Different strokes for different folks! Pp. 334 through 340 contain interesting summaries of the most celebrated deep sky objects visited by amateurs in any age, including the Great Nebula in Orion, the Andromeda Galaxy (nebula in Denning’s day), the Dumbbell, Ring and Crab Nebula. Spiral nebulae such as M51 and M91, and what Denning refers to as “elliptical nebulae” including M81 & M82. He also discusses the prominent globular clusters, such as M13 in Hercules, as well as M2, M3, M5, M15 and M80. Denning also mentions the magnificent Omega Centauri, the delight of antipodean skies, which Sir John Herschel referred to as, “beyond all comparison the richest and largest object of the kind in the heavens.” In the final pages of the book, Denning presents a much more extensive list of deep sky objects, together with some brief descriptive notes. He also includes 10 nebulae on p. 342, all discovered as a result of his own comet sweeps near the north pole, between 1889 and 1890. Denning provides us with some details of the techniques he used while sweeping the sky for nebulae. Again, he stresses the considerable advantages of decent aperture: Those who sweep for nebulae must have the means of determining positions, and a small telescope will be inadequate to the work involved. A reflector of at least 10 inches, or a refractor of 8 inches, will be required; and a still larger instrument is desirable, for to cope successfully with objects of this faint character needs considerable grasp of light. The power employed should be moderate; it must be high enough to reveal a very small nebula, but not so high as to obliterate a large, diffused, and faint nebula………With a low power a very extensive field will be obtained, and a large part of the sky may soon be examined, but it will be done ineffectively. It is better to use a moderately high power, and thoroughly sweeping a small region. The work is somewhat different to comet sweeping; it must proceed more slowly and requires greater caution, for every field has to be attentively and steadily scanned. If the telescope is kept in motion, a faint nebula will pass unseen. Some of these objects are so feeble that they are only to be glimpsed by averted vision. When the eye is directed, say to the E. side, a faint momentary glow comes from the west side of the field; but the observer discerns nothing on looking directly on the object. pp. 339–40

Author’s note:  The reader will note that Denning clearly understood the concept of using averted vision to detect objects on the precipice of invisibility, the oldest unambiguous reference this author has thus far come across, and clear evidence that he was indeed a highly skilled and accomplished deep sky observer. In addition, Denning places a 10-inch reflector (presumably of the silver on glass variety) on par with an 8-inch refractor for deep sky work. Denning ends this chapter with an encouraging note to other amateurs: The discovery of new nebulae offers an inviting field to amateurs. Vast numbers of these objects have escaped previous observation, for though the sky has been swept again and again, its stores have not been nearly exhausted….. The region immediately outlying known objects may also be regarded as prolific ground for new discoveries. p. 341

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 fterword: The Significance of Denning’s Literary Work A for the Contemporary Amateur In surveying Denning’s masterful work, it is clear that there is little that the modern visual observer can add to what has already been documented by our Victorian forebears. In an age where many amateurs deliberately exaggerate their findings with various telescopes, Denning’s masterly survey of the hobby puts all things in perspective. Judging by the forums, where some contemporary amateurs claim a 3-inch telescope can show you more than a 6 inch telescope. Denning says “no!” Another contemporary amateur claims to have seen more than anyone who came before. Denning says, “not so!” The armchair astronomer claims that clear skies are few and far between. Denning shows us that this is false. Conventional wisdom insists that refractors must be the instrument of choice in divining the trickiest double stars. Denning’s writings from over a century ago prove otherwise. In short, Telescopic Work for Starlight Evenings, is a breath of fresh air and a pleasure to read. It ought to be on the bookshelves of all amateur astronomers today.

Sources Denning, W.F.: Telescopic Work for Starlight Evenings. Cornell University Library, New  York (2010) Philips, T.E.R.: Hutchinson’s Splendour of the Heavens, vol. 1. Hutchinson & Co, London (1923)

Chapter 20

The Astronomical Legacy of Asaph Hall

Today’s professional astronomers are highly specialized folk. Almost certainly, an astronomer who is an expert in planetary orbits say, will know relatively little about the cutting edge of stellar astrophysics and vice versa. The exponential increase in our knowledge of the Universe has made specialization a necessity. But there was once a time when astronomers were highly knowledgeable in almost all avenues of their discipline. This is the story of one of the last of this generation of ‘Jack of all trades’ astronomer; the famous discoverer of the tiny Martian satellites, Asaph Hall (Fig. 20.1). Like others of his ilk, Hall’s early years were predictably obscure. Born in the town of Goshen, Connecticut in 1829, he was the son of a ne’er do well clockmaker and small land holder, who, after loading up his wagon, would peddle his wares as far south as Georgia. Hall’s childhood was quintessentially bucolic until his father died in early September, 1842, when young Asaph was only 13  years old. Unfortunately, his father’s passing did nothing to improve the family’s financial lot, their land still being heavily mortgaged, but the evidence suggests that they were able to retain a holding of a small dairy farm, making a modest income producing and selling cheese. Even at this early age, Hall was an avid reader and adventurer in thought. His father before him had a modest collection of books – the works of Edward Gibbon and David Hume among them – which he read with great interest. With a roof over his head but the wolf never being too far from the door, Hall accepted a 3 year carpentry apprenticeship at age 16. Any meager wages he would receive went to his mother and his five siblings. His apprenticeship allowed him to secure work on various house building projects earning about $1.50 a day. By 1854, he had saved $300 to put towards the advancement of a proper college education. To that end, he enrolled in classes at Central College in New  York. Here he developed a strong aptitude and love for mathematics. It was also here that he would meet his bride to be, Miss Chloe Angeline Stickney, who had graduated in 1855. They were soon married and moved to Ann Arbor, Michigan, where Hall entered the university as a sophomore under © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_20

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Fig. 20.1  Asaph Hall (1829–1907). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Professor_Asaph_ Hall.jpg)

the supervision  of Professor Franz Brunnow, who provided him with a thorough grounding in celestial mechanics and sound practical instruction on the handling of precision astronomical instruments. Still, his education could only continue as long as the money didn’t run out and Hall found himself working as a carpenter in locations that took him away from his young bride for weeks and months at a time. Eventually, he joined her at Shalersville, Ohio, after she had secured teaching posts for them both. There is a curious story of how Hall, having become fixated on an orbital problem, arose and walked 15 miles along a dirt road to the library at Western Reserve College in Hudson. When he arrived he was covered in dust and the librarian at first mistook him for a vagrant. Yet when he asked if he could consult Laplace’s Mechanique Celeste, he quickly changed his mind and came to Hall’s assistance. His desire to become a professional astronomer became stronger and stronger in the passing months. After working as a schoolmaster by day, he’d burn the midnight oil studying the classic works of the world’s great mathematical astronomers; Lagrange, Laplace, Gauss, Hansen and Bessel amongst others. In 1856, Hall applied for and successfully secured an astronomy post at Harvard Observatory, which he took up in August 1857. Many years later he recalled how he and his wife: [R]eceived a kind reception from Professor W.C. Bond. Professor G.P Bond (his son) was absent on a trip to New Hampshire. I was set to work making observations for time, and was shown how to use the transit circle, to read the chronograph sheets, to work out the

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i­nstrumental constants, and to compare and rate the chronometers. Professor Bond was very kind and pleasant, so that under his guidance, I made good progress. I worked hard and spent most of my time at the observatory…. After a month or six weeks Professor G.P. Bond returned. He seemed a little surprised to find an assistant in the observatory, and doing so much work. He had a free talk with me, and found out that I had a wife, $25 in cash and a salary of $3 a week. He told me very frankly that I had better quit astronomy, for he felt sure I would starve. I laughed at this, and told him my wife and I had made up our minds that we were used to sailing close to the wind, and felt sure we would pull through.

Hall and his family stayed at Harvard Observatory for 5 years, where he cultivated a special talent for calculating the elements of cometary and asteroid orbits. But the ravages of the American Civil War took their toll and the economy suffered. Hall was forced to look for a better paying job to support his young family. But fortune smiled on him. By 1863, he had secured a post as Professor of Mathematics at the US Naval Observatory in Washington, D.C, which offered him and his family the financial security he sought. Yet it was not without its problems. The blast of the cannon fire from the battle of Bull Run could be heard from the observatory on several occasions, creating anxiety amongst the staff. Hall had to ask for time off to search for wounded relatives or friends of the family and brought several to the house in which he and his wife were residing and there they nursed them. In September, not a month after the second Bull Run defeat, more wounded from the Antietam battlefield arrived. It all proved too much for Hall. The intense summer heat, the all-night vigils at the telescope, together with his part-time role as nurse took their toll. He succumbed to jaundice, the effects of which he slowly recovered from over the next 2 years. The following spring, smallpox broke out in the vicinity and, when 40 cases of the dreaded disease were reported at one time, Hall sent his wife and son back to New England. Even under such conditions Hall continued to work diligently, conducting observations with the 9.6-inch Merz refractor installed at the observatory. On 22nd of August 1863 very special visitors came to the Observatory; President Lincoln and his secretary, John Hay. Hall, finding himself alone and on duty, showed the Commander in Chief the glories of the Moon and the lovely orange star, Arcturus, through the big Merz glass. They must have been impressed, for several nights later, according to one account garnered years later by Hall’s son (also an astronomer), his father heard a knock at the trap door. After leisurely completing his observation, he made his way to the lift door, when up through the floor the tall President raised his head. Lincoln had come unattended through the dark streets to inquire why the Moon had appeared inverted in the telescope. That’s because the surveyor’s telescopes he had once used showed objects the right way up. Hall explained that the astronomical telescope’s optics had no need to present rounded celestial bodies as they are. He and Lincoln proceeded to chat about astronomy for a considerable while, after which he returned to the White House satisfied with the answers Hall had provided him. With the Civil War over, more prosperous times were enjoyed and funds were raised for a better telescope to take the place of the 9.6 inch Merz. Indeed, a number of private individuals had access to even larger instruments than this – a fact that

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Fig. 20.2  The 26-inch Clark refractor at the U. S. Naval Observatory, Washington D. C. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Moons_of_Mars#/media/File:Usnotelescope-equalized-1.png

was becoming somewhat of an embarrassment for the Observatory Director. The great American telescope maker Alvan Clark & Sons was consulted whereupon a 26 inch instrument was commissioned (with funds being supplied by the federal government) – which enjoyed the distinction of being the largest telescope in the world for a short spell. The instrument was installed in 1873 under the direction of Simon Newcomb. But by 1875, Hall was given principle responsibility for its use. The 26-inch Clark was arguably one of the finest refractors ever built, with several authors having noted its excellent optics in independent tests. Its raison d’etre was to provide a more accurate positional measurement of the faint satellites of the outer planets, which, in turn, allowed astronomers to more accurately ascertain the masses of these worlds (Fig. 20.2). Jupiter, Saturn, Uranus and Neptune were more or less taken care of, owing to the discovery of their systems of satellites. The exception however was the Red Planet, Mars, which had no known natural satellites and thus its mass could only be guesstimated – which varied unsatisfactorily between 9% and 13% of the Earth’s planetary mass – owing to gravitational perturbations from the Earth and Jupiter. If he had anything to go by, the odds were stacked against Hall. Some highly skilled observers, such as Sir William Herschel and Heinrich D’Arrest, who had searched the vicinity of the planet in 1783 and 1862–64, respectively, came up empty handed. In the end, it was gentle encouragement from his wife that sustained

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Hall’s energies, as well as confidence in the optical superiority of the new, giant telescope at his disposal. An excellent opportunity afforded itself in August 1877, when Mars got as near as 35 million miles from the Earth. His diaries wrote: At first my attention was directed to faint objects at some distance from Mars; but all these proving to be fixed stars. I began to examine the region close to the planet and within the glare of light surrounding it. This was done by keeping the planet just outside the field of view, and turning the eyepiece so as to pass completely around the planet. While making this examination, on the night of August 11, I found a faint object on the following [east] side and a little north of the planet, but had barely time to secure an observation of its position when fog from the Potomac River stopped the work. Cloudy weather intervened for several days. On the night of August 15, the sky cleared up at 11 o’ clock…but the atmosphere was in a very bad condition, and nothing was seen of the object, which we now know was so near the planet as to be invisible. On August 16, the object was found again on the following side of the planet and the observations of that night showed that it was moving with the planet and, if a satellite was near one of its elongations. On August 17, while waiting and watching for the outer satellite, I discovered the inner one. The observations of the 17th and 18th put beyond doubt the character of these objects.

George Anderson, his faithful assistant at the great telescope, also confirmed the sighting of these two new satellites. The following evening (August 18th) he was joined in the dome by several other astronomers including Simon Newcomb, W. Harkness and D. P. Todd. Once these astronomers had confirmed their existence at the eyepiece, news of the great discovery was dispatched to the press. In the hours that followed, Hall became an international celebrity, showered with congratulatory telegrams from well-wishers across the United States and Europe. In the coming weeks, Professor Hall received more letters from astronomers who had claimed that they had sighted the elusive Martian satellites- and some with much smaller instruments to boot. One curious Pennsylvanian amateur, equipped with a 2-inch telescope informed Hall that, “I have discovered a satellite and it goes round the primary in five seconds!” Hall later named the Martian satellites, Phobos (‘fear’) and Deimos (‘panic’). after the sons of Ares, the Roman god of war. Yet, it appears that, with hindsight, Hall was a modest man in reference to his achievement. “Mr. George P. Bond should have discovered these satellites in 1862,” he quipped, “his telescope was powerful enough to reveal them.” By the autumn of 1879, the satellites were again observed in almost exactly the positions they were predicted to be in. Hall’s discovery inspired budding young astronomers such as the temperate Tennessean, Edward Emerson Barnard (1857–1923) to turn a telescope skyward. Though he achieved fame for visually discovering the tiny moons of the Red Planet, arguably Hall’s greatest work was in the specialized field of double stars. Skilled with a filar micrometer, in 1880 he gathered together his measures of 1614 pairs observed with the 9.6-inch Merz and the great 26-inch Clark refractor. In addition, he observed a spot on the surface of Saturn in 1886 that helped him to accurately determine its period of rotation; 10.75 h, which compares well with today’s figure of 10 h 14 min (at equatorial latitudes).

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Fig. 20.3  Hall’s Gold Medal of the Royal Astronomical Society. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Asaph_Hall#/media/ File:Asaph_Hall_Gold_ Medal.jpg)

Hall was also interested in the hypothetical planet lurking between the Sun and Mercury  – the elusive planet Vulcan  – a world conjured up by the researches of Urbain Le Verrier, conducting observations of the space in the vicinity of the total solar eclipse of July 29, 1878 but without success. That chestnut was cracked by Albert Einstein in the corpus of his General Theory of Relativity (1916). In 1879 Hall received the Gold Medal of the Royal Astronomical Society, the organization’s highest honor. In 1896, he returned to Harvard where he became a professor of astronomy. Hall published a number of works including, Determination of Aberration Constant, which he wrote while working as the Director of the Detroit Observatory at the University of Michigan. In this work, he used parallax on his measurements to more accurately arrive at the size and distance of the Pleiades cluster. Hall also did original work in mathematical astronomy, particularly the retrograde motion in the line of apsides of the orbit of Hyperion. Craters on the Moon and Phobos are also named in his honor. He died on November 22, 1907, age 78 (Fig. 20.3). Hall’s contributions to astronomy have had an undeniable impact on science. His rise to academic prominence despite an impoverished early life is admirable in its own right and his achievements certainly rank him as one of the greatest old-school visual observers in the pantheon of classical astronomy; a man who was equally at home calculating some difficult problem in spherical trigonometry as he was behind the eyepiece of a giant refracting telescope. Asaph Hall, we remember you!

Sources

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Sources Clerk, A.: A Popular History of Astronomy During the Nineteenth Century. Cornell University Press, New York (2009) Hall, A.: An Obituary. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bib code=1908AN....177..127E&db_key=AST&page_ind=0&plate_select=NO&data_ type=GIF&type=SCREEN_GIF&classic=YES Hockey, T.: Biographical Encyclopedia of Astronomers. Springer, New York (2009) Rudaux, L., De Vacouleurs, G.: Larousse Encyclopedia of Astronomy. Hamlyn, Feltham (1959)

Chapter 21

The Life and Work of Charles Grover (1842–1921)

Memory is one of humanity’s supreme endowments. Each of us acts today and hopes for tomorrow in the light of past experiences that have been woven into a life-story. When we want to know someone else, we ask that person to tell us something of the story of his or her life, for in this way personal identity is disclosed. To be a self is to have a personal history. This is what defines one’s uniqueness.

Bernhard W. Anderson: from The Living World of the Old Testament (1988). The British Victorian era was, for the most part, the age of grand amateur astronomers – men of great personal wealth who erected large (for the time) telescopes on lavish country estates to observe the heavenly creation. But while it was certainly difficult to get on in scientific circles unless one were male and well connected, there were always exceptions, men and women with the right personal attributes – an admixture of natural curiosity, talent and diligence – who managed to break the shackles of their lowly social status, to gain the admiration of everyone, irrespective of class. Such is the story of the Englishman, Charles Grover (1842–1921) (Fig. 21.1).

Days of Youth Charles was born on March 7, 1842, the second son of John Grover, a shoemaker, and Eliza Benwell, a shoe binder. Misfortune struck early for Charles with the death of his mother aged only 25 years, when the boy was still an infant, only 2 months old. His father passed away when Charles had barely reached his 8th birthday. Grover’s memoirs state that he was consigned to the care of his grandmother, who lived at 37 Church Street, Chesham. Like all Victorians of lowly status, his early education was basic and often checkered. Attending the British School at Chesham, Charles received instruction in reading, writing and arithmetic, paid for by wealthy benefactors and Christian charities. And like so many impoverished Victorians, Grover supplemented his education by reciting the Holy Bible from home and © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_21

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Fig. 21.1  Charles Grover (c. 1907) at the telescope at Rousdon Observatory, Devon. (Image courtesy of Wiki Commons. http:// www.steammill. phlegethon.org)

reading, “with eagerness any books that came my way.” Yet it is unclear what other literature he could have gained access to. His biographer, Barbara Slater, notes that the young Grover might have benefitted from the new ‘Circulating Libraries’ and Mechanics Institutes that were being established up and down the country during the mid-nineteenth century. While attending the British school, Grover was lucky enough to have a kindly schoolmaster, a one William Osbourne, who recognized Charles‘latent talent for sketching and encouraged him to pursue it as best he could. But that modicum of security was to run out in 1854, when Grover’s grandmother, who acted as the boy’s guardian, passed away. It is unclear who took over the custody of the 12-year- old Charles in the aftermath of his grandmother’s death, but some sources suggest that he may have been cared for by other relatives who lived in the catchment area. What is clear is that boys of that age and social status, particularly from rural communities, more often than not ended their formal education to take up an apprenticeship. The young Charles Grover secured such an arrangement by being consigned to a local brush maker, Henry Rose. In those days, such an apprenticeship was considered to be near the bottom of the heap of artisanal work available, but Grover accepted the position with graciousness, spending the next 15  years in

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Fig. 21.2  A sketch of the appearance of Donati’s Comet as it appeared in the autumn of 1858. Note its head passing close to the bright star Arcturus, and the Big Dipper asterism on the upper right. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Comet_Donati#/media/ File:CometDonati.jpg)

Roses’ employ. During this time, Grover courted Elizabeth Birch and married her in August 1862. Though undoubtedly Grover accepted his lot as a brushmaker, he longed for something better. In his memoirs he writes, “My mind was not in this and all my spare time was devoted to such books as I could get and the pursuit of general knowledge.” Grover’s world changed utterly and forever in 1858 when he observed Donati’s Comet with feverish delight. Night after night, he traced its path against the background stars. On the evening of October 5, 1858, the comet passed near the bright star, Arcturus, in Bootes. It was at this stage that Grover committed himself to learning the constellations. On each available clear night, he would watch the stars and keep a diary of his experiences. On the night of May 8 1859, he observed a most curious phenomenon; a bright star had come very close to the Moon before disappearing behind it! Consulting an astronomical almanac, Grover discovered that the bright star was in fact the planet Saturn. It was at this stage that Grover realized that he needed a telescope (Fig. 21.2). As one might expect, refined instruments were completely out of the question for a man of such modest means but he saved enough coin to purchase an old ship’s spyglass for the princely sum of 10/−. But where others would have soon discarded

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such a crude instrument, Grover embraced it with a boyish enthusiasm. “To me,” he later wrote, “it was a wonderful instrument.” Indeed, he was to use it for two whole years, during which time, it showed him the ever-changing cadence of Jupiter’s large satellites, the battered lunar countenance with its multitudinous craters, the phases of the brilliant planet Venus and some of the brighter star clusters, most notably, the Pleiades in Taurus, as well the Beehive Cluster (Praesepe) in Cancer. After seeing all he could with the spyglass, he sold it to raise funds for something a little better. But he found that even the smallest achromatic telescopes of the day were prohibitively expensive. Indeed, the least expensive 2-inch achromat available at the time would have set him back £3 – a sum that represented more than a month’s salary. Undeterred, Grover resorted to making something from his own hand. After acquiring a biconvex lens of three– inch aperture and five– foot focus, he mounted the lens in a zinc tube and, at the other end, a crude eyepiece holder which slid along a makeshift ‘eyehole’. A modern amateur would have balked at such a contraption – which was more at home in the eighteenth century than the nineteenth- but not Charles Grover. Despite having severe spherical and chromatic aberrations, he described its (low power) field of view as ‘brilliant’. With this instrument, Grover observed the Great Comet of 1861 and returned to the Pleiades cluster, carefully recording the positions of 52 members (Fig. 21.3). In 1862, Grover had knocked together enough funds to purchase his first ‘proper’ instrument, a 2-inch achromatic refractor of 36-inch focal length, made by the Mancunian telescope maker, J.  T. Slugg & Co. The instrument was fitted with a pancratic ocular delivering a range of magnifications of 50, 60 and 80 diameters. After testing it out, Grover proclaimed it optically excellent. Observing the Giant Planet and some selected double and multiple stars with it, he declared: “Though small in size this instrument performs well and the beautiful definition of its object glass cannot be surpassed. The appearance of Jupiter in this instrument with a power of 80 and a clear sky is truly beautiful, the belts and cloudy spots being seen with great clearness. Double, triple and quadruple stars are very clearly seen.”

Fig. 21.3  A spyglass like this launched the telescopic career of Charles Grover. (Image by the author)

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With this new and greatly improved telescope, Grover embarked upon systematic observations of the Sun, Moon, brighter planets and the deep sky. During the 1862–3 apparition of Saturn, Grover recorded the gradual disappearance of the planet’s ring system as it came into the plane of Earth’s orbit. In retrospect, this was a remarkable series of observations, made by such a young observer and modest instrument. Apart from a brief hiatus corresponding to his marriage, Grover was a regular observer, making observations on each available clear night. This is all the more remarkable as he was also keeping down a full-time job which often involved early starts. Grover’s new-found passion for astronomy reflected a general increase in the popularity of the hobby amongst the lower and middle classes. The underlying causes for this increased interest from the lower echelons of Victorian society may have been attributed to the launching of a number of new periodicals including the Astronomical Register. By 1865, Grover had published some observations of the lunar surface as seen through his small telescope. His records soon came to the attention of more established astronomers, particularly the ‘father of all amateur astronomers,’ the Reverend Thomas W. Webb, based at Hardwicke, Gloucestershire. It was about this time also that Grover began writing to the famous astronomer and was delighted to see that Webb would write him back, encouraging the young astronomer in his studies. Indeed, Grover was to often speak of Webb’s ‘kind and genial nature.’ Moreover, Webb was to the gift another 2-inch refractor (of higher pedigree) to Grover to carry on his work. Grover was to use this instrument to conduct several impressive drawings of Mars during the winter of 1868–69.

Establishing a Good Name Webb evidently saw in Grover the makings of a first-rate observer, and upon calling attention to his work among his distinguished friends, he was soon invited to the country estate of Dr. John Lee at Hartwell House, Buckinghamshire, the well-to-do barrister and keen amateur astronomer, who had erected a magnificent 16-foot revolving dome around the 5.9-inch Tulley achromatic refractor once owned by Admiral W. H. Smyth. Grover even got a chance to look through the famous instrument having vividly recalled the beautiful view of Saturn at 240x through the telescope. Grover was fascinated with all the accoutrements Dr. Lee had acquired to fully equip his observatory. Like a kid in a candy store, Grover recalled seeing all manner of mechanical devices – orreries both large and small, and an antique seventeenth century non-achromatic telescope (c. 1650) furnished with a two- inch singlet lens in a 10-foot tube made of vellum. In the room annexed to the main observatory, Grover noted a 3.75-inch transit telescope of 5 foot focus. But the device that most attracted Grover’s attention was the precision micrometer used by Admiral W. H. Smyth. Indeed, it was to inspire Grover to construct his own primitive micrometer for use with his 2-inch achromatic to carry out some double star measures. The mechanical details of this device were published in the January 1866 issue of the Intellectual Observer, too much acclaim.

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Despite what some contemporary amateurs have maintained, Dr. Lee and his distinguished astronomical acquaintances were not ‘toffs’ out to reaffirm their own superiority over others in society. Grover’s diaries reveal the very opposite; that of a community which rewarded observers based on merit. In his memoirs Grover noted: The Dr. received me with the greatest kindness, made the most minute enquiries as to my circumstances, instrument, books etc, and looked carefully through my manuscript observations which I had been asked to bring for his inspection, and before I left he expressed himself as much surprised and pleased by the accuracy of the work I had accomplished with very small and limited means, made me a liberal pecuniary present and gave me a large number of books.

Grover’s visit to Hartwell House allowed him to greatly broaden his circle of astronomical acquaintances, including the famous telescope maker, George With, creator of high quality silver-on glass reflecting telescopes. Indeed, With gifted Grover a fine 6.5 inch reflector for his own use. Soon he was to begin work making a suitable mount for the instrument, supervised by the Reverend Cooper Key and George Knott. Before long, Grover had made a fine equatorial mounting for the telescope, an instrument that he would use for many years to come. Such an instrument must have represented a huge leap forward for Grover, accustomed as he was to looking through small achromatic refractors. Grover’s memoirs describe his initial reaction to his 6.5-inch silver-on-glass reflector. It had, he said,“splendid definition” and” great light grasp.” It was around this time that Grover began a correspondence with another instrument maker of note, John Browning, who had set up a small workshop in London, and who invited Grover to join him as his assistant. Though the salary was still modest, it was considerably better than what he was earning as a brushmaker. It was an opportunity too good to let go and so, at the age of 27 (1869), Charles, his wife and five-year-old son, George, moved to the ‘Big Smoke’ in search of new adventures and fortunes (Fig. 21.4). Fig. 21.4 The distinguished instrument maker, John Browning (1831–1925). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ John_ Browning_%28scientific_ instrument_maker%29#/ media/File:John_ Browning_1.png)

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The Grovers took the move to London in their stride. No longer would Charles have to endure working for long hours on mind-numbing tasks. Now he could put his back into a job that was very much closer to his heart, assembling, testing and repairing precision astronomical equipment, as well as travelling the length and breadth of the country in order to aid in the proper setting up of the instruments for Browning’s extensive clientele. In 1867 Browning had published his influential work, A Plea for Reflectors, in which he enthusiastically endorsed the new silver-on-glass Newtonian telescopes, highlighting their many advantages, not least of which was cost. Browning was also a keen and well-established observer of his own, possessing a first-rate 12.25-inch equatorial reflector in his own back garden in Clapham. Charles’ memoirs recount many episodes using Browning’s personal instrument (Fig. 21.5).

Fig. 21.5  An advertisement by Browning for one of his reflecting telescopes. (Image by the author)

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Maturity During much of the 1870s, Grover attended many lectures delivered by distinguished speakers in scientific circles. Indeed, Grover operated a magic lantern at many of the most prestigious meetings of the Royal Astronomical Society (RAS), giving him a ‘ringside seat,’ as it were, to the scientific content therein. After moving to more comfortable lodgings at Wellington Buildings, Chelsea, their second son was born in February 1881 but sadly died on July 13 of the same year. Curiously, his own records show that he was busy observing Tebbutt’s Comet on the very evening his second son passed away. What are we to make of this? Doubtless some would quip that this was rather cruel, indifferent or inhumane. It must be remembered that Grover was a man of his time and Victorian fathers were expected to rule their hearts with their heads. What is more, infant death for much of the Victorian era was only marginally (if anything) better than the child mortality rate experienced in ancient Rome. Thus, the average Victorian was much more conditioned to death than we are today. That said, Grover probably coped with his loss in the only way he knew how – by getting on with things. Going onto the roof to observe might have been his way of escaping the ordeal, at least temporarily. This author would like to think that a tear came to his eye, concealed in the darkness of the night, as he set up his telescope for work. Grover’s move to London greatly increased his circle of astronomical aquaintances, which included G.B. Airy, Warren De La Rue, J.C Adams, Charles Pritchard, Richard Proctor and William Lassell. Though many of the lectures of the RAS were fascinating to Grover, he found others dull and deliberately chauvanistic, orientated more toward the upper classes. Another member of the RAS known to Grover was Captain William Noble, who, having become totally disillusioned by the pomp and ceremony of the RAS, decided to found a completely new and more inclusive society. Called the British Astronomical Association (BAA), it held its first meetings in 1890 and was open to everyone, male and female, for a modest annual fee.

New Adventures With more connections than ever before, Grover found that further opportunities knocked. And his skill in the operation of sophisticated astronomical tools meant that his services were in great demand. In 1882 Charles left Browning’s workshop to go to Australia as assistant to the young Cuthbert Peek (whose father Sir Henry Peek was a baronet and a member of Parliament), as part of a Royal Geographical Society (RGS) expedition to observe the transit of Venus, which was due to occur on December 7, 1882. Accompanying Grover and Peek on board the Liguria was Captain William Morris of the Royal Engineers and a lower ranking officer, Gunner Bailey of the Marine Artillery, Lieutenant Leonard Darwin, son of the famous naturalist, Charles Darwin, and his wife, Elizabeth.

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The 45 day journey by sea to Australia was, for the most part, comfortable. The well-to-do group enjoyed first class quarters, whilst Charles had to contend with second class accommodation, a situation that made him acutely aware of his standing in the social order, but which he accepted without complaint. His new employer, Cuthbert Peek, was a gentleman through and through however, and never made Grover feel out of place. But the diaries of Leonard Darwin reveal a moody and ungracious disposition, constantly complaining about the bad food on board, as well as expressing a general boredom with the journey. The reader will also note that Darwin had been a prominent member of the Eugenics Society back in England, something that did him no good in retrospect, basing his ideas on his father’s theory of evolution. Peek had arranged the transport of a fine 6.4-inch f/12 Merz refractor, which he purchased second hand from a one Mr. Lettsom of Lower Norwood. Its relatively short focus made it a good choice for transport and Charles was already intimately familiar with its set up. Peek also brought along a small portable telescope. Grover had to make do with a good set of high powered binoculars. As luck would have it, the crew got a chance to see a remarkable apparition – the great September Comet of 1882 – discovered by the astronomer, W. H. Finlay, at the Cape of Good Hope on September 7, just 10 days before perihelion passage. Charles made copious notes while on board ship of this famous sungrazer (it came to within 1.5 degrees of the Sun). Smaller equatorial telescopes were used by Gunner Bailey, Darwin and Captain Morris. The Liguria arrived off Melbourne on October 8, where the crew enjoyed a few days leisure, exploring the harbor and the city of the New World. Charles, as usual, recorded his experiences with copious notes, which included a visit to Melbourne Observatory, which housed an 8-inch Cooke equatorial and the centerpiece of attraction; the great Melbourne Telescope; a leviathan built by Howard Grubb of Dublin and installed in 1868, with a 48 inch mirror made of speculum metal – the last great telescope to have been fitted with a speculum metal mirror. The enormity of the instrument – fully 5 feet across and 40 feet in length – amazed everyone but especially Charles Grover (Fig. 21.6). Mechanically excellent, the 48-inch reflector had a great name but optically it was apparently suspect, having poor defining power on high resolution objects like planets and globular clusters. Despite these limitations, it was reputedly a most powerful light bucket, built to continue the study of the skies of the southern hemisphere, begun by Sir John Herschel in 1847 at the Cape of Good Hope, South Africa. From there, the expedition team set sail on the Liguria for Sydney, where Charles again had time to visit the well-endowed city Observatory overlooking the harbor. A keen sketcher, Grover recorded some fine details of its two vaulted astronomical ‘cathedrals’ on the afternoon of October 18. The main instrument was a majestic 11.3 inch equatorial refractor, erected under a dome of Munz metal (a copper alloy), its green oxide veneer gleaming in the strong, Australian Sun. Another smaller dome housed a 7.5 inch Merz achromatic and several transit instruments built by the British firm, Troughton & Simms. The party was shown round by the resident

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Fig. 21.6  The great 48″ Melbourne telescope, as it appeared c. 1910. (Image courtesy of the Australian National University. http://amazingspace.org/resources/explorations/groundup/lesson/ scopes/melbourne/scope.php)

astronomer, Mr. H. C. Russell, who Grover remembers with affection. Russell had already set up 3- and 4-inch refractors for the up-and-coming transit. After enjoying a week in Sydney, Grover had to supervise the safe transfer of the delicate equipment from the Liguria to a small steam boat, the SS Katoomba, to complete the short voyage to Brisbane, arriving on the evening of October 26. From there, the RGS expeditionary team had to take a train to Macalister Government Station. Finally, a 4-horse drawn wagon carried them the last 12 miles across a flat, grassy plain to their destination at Jimbour, on the Darling Downs of Queensland. It was now early November, a good month before the eagerly awaited celestial event. The expedition team enjoyed fairly comfortable lodgings in a 22-room mansion built by wealthy colonial landowners. Mrs. Darwin took it upon herself to manage the day to day running of the house at Jimbour. By the evening of November 6, Grover re-assembled the 6.4 Merz instrument upon its heavy equatorial mount and was delighted to report that not a single screw was missing and the clock drive worked as smoothly as it had done back in England. Two other huts were set up by Captain Morris and Lieutenant Darwin, which housed slightly smaller telescopes (6 inch Cooke equatorials), connected by telegraph to Sydney Observatory. By November 12, all the instruments were up and running and ready to go. No time was lost carrying out night time observations and the site was deemed excellent. “We soon have striking proof of the purity of the air at this place over 1,000 feet above sea level,” Grover recounted, “and it proved an ideal place for observations, only two cloudy nights occurring in the six weeks we were here.” A

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Fig. 21.7  Cuthbert Peek seen looking through the 6.4-inch Merz refractor at Jimbour, with Charles Grover assisting. (Image by the author)

large catalog of double stars were examined with the telescopes but time was set aside to look at deep sky objects too, especially the nebula around the star Eta Argus (now referred to as Eta Carinae), on which Peek would write an interesting memoir upon his return to England in August 1883. The bright planets, Jupiter and Saturn, were also intensely scrutinized by the British team. Grover was especially impressed with the view of Saturn as seen through the 6.4 inch Merz. The planet, “was seen with wonderful distinctness”, he wrote, “and it is not too much to say that all that is shown of this planet on the beautiful plates of De La Rue, the drawings of the late W. R. Dawes, or the figures of the Washington observers with their great telescope were well seen with this instrument.” The makeshift observatories soon became the center of curiosity for the local natives, who would come by the site to peer at the ‘strange’ equipment and get a chance to observe the heavens. Peek arranged for the observatory to be opened an hour or so before sunset to allow for public viewing of Jupiter and Saturn. Usually, serious observations only commenced after local midnight and continued until the break of dawn. Grover revealed himself to be a man of his time in his record of the aboriginal people he had encountered. Though he does refer to them as ‘blacks’ and was rather taken aback by their relative nakedness and rumors of their cannibalistic tendencies, he never denied their basic humanity (Fig. 21.7).

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As the date of the transit of Venus approached, their luck with clement weather began to run out. On the eve of the event (December 6), a bright sunny morning gave way to thick clouds, followed by thunder, lightning and heavy rain. The deluge persisted into the morning of December 7, with the result that the transit could not even be glimpsed! Throughout that depressing morning, telegrams were received from observers based in Sydney, Brisbane and Melbourne disclosing a similar tale; a large swathe of Eastern Australia was clouded out for the event. In a cruel irony however, the next morning at Jimbour was clear as gin! The sense of disappointment was especially trenchant for Darwin, who had also failed to see the transit of Venus in New Zealand in December 1874: “We have nothing to show for all these weeks of work,” he wrote, “there are few people who have been twice round the world to see a thing without seeing it.”

Homecoming Throughout the long journey to Australia, Grover’s wages were paid directly to his wife Elizabeth in London, as all his expenses were taken care of by Cuthbert Peek. Grover’s son, who by now had reached adulthood, had already embarked on a career as a school teacher. Grover, together with the 6.4-inch Merz equatorial, was to return to England ahead of Peek, boarding the British East India steamship HMS Merkara on the third day of January 1883. The journey, which took a route across the Indian Ocean, stopped briefly at Batavia before passing through the Suez Canal into the Mediterranean, and onward to England. Around the same time, Peek had wrote to his uncle, highly recommending Grover for a post at the family country residence in Rousdon (acquired by the Peeks in the 1870s), Devonshire, a sleepy little village by the sea, where he had entertained serious thoughts of establishing an astronomical observatory. Peek was to offer Grover a permanent position there so that he might carry out further researches from its pristine, dark skies. It was an offer too good to pass up. So, shortly after his arrival back in England in February 1883, Grover, accompanied by one of Peek’s men, safely transported the astronomical equipment to Rousdon, and later that year, Charles and his wife took up residence in the eastern lodge of the estate, just a short walk from where a permanent astronomical and meteorological observatory would be set up. The Grovers were to remain there for the remainder of their lives.

Observer in Charge A makeshift wooden observatory with a sliding roof was established at Rousdon as early as 1884, together with a simple meteorological station, but by 1885 provision was made to establish a proper observatory, made of fine teak timber, and resting on

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a concrete foundation. It had a properly rotating dome where the main instrument – the 6.4-inch equatorial Merz achromatic – was housed. A photographic dark room was set immediately beneath the dome, with a flight of steps connecting the two. Provision was also made to house a small transit instrument, by Troughton & Simms, of 2 inch aperture and 2 foot focal length. As well as Grover’s astronomical duties, he also made a series of meteorological readings, twice each day, and 12 h apart – at 9 a.m. and 9 p.m. These included air pressure measurements, reading off dry and wet bulb thermometers, wind speed measures using an anemometer, as well as the retrieval of data from a sunshine gauge. The Merz equatorial was outfitted with a series of eyepieces delivering powers of 64, 90, 136, 206 and 310 diameters. A Barlow lens afforded even higher powers up to 620x. In addition, a precision micrometer by Hilger could be coupled to the telescope for precise  astrometric measurements. Grover once remarked on the sheer elegance of the Cooke mounting for the main instrument: “A very simple and well-constructed clock movement carries the telescope with a motion so smooth and uniform that star remains for a considerable time bisected by the micrometer wire and by a regulating screw the rate can be at once made to coincide with Solar, Lunar or Sidereal time.” The decade leading up to the dawn of the twentieth century was arguably the happiest and (certainly) the most productive years of Grover’s life. Here in this bucolic setting, far from the smog and squalor of the Victorian cities, he enjoyed good health, better pay and ready access to a magnificent telescope, just a stone’s throw from his home. As well as carrying out occasional measures of double stars, as well as lunar and planetary observing, it was at Rousdon that Grover embarked on a systematic study of variable stars, inspired by a circular written by the famous American astronomer, E.  C. Pickering, who actively encouraged more serious observers to take up the gauntlet. Unlike many other kinds of astronomical observing, which can be enjoyed on a quasi-casual basis, specializing in long-period variable star observing requires a concentration of will going well beyond the usual call of duty. Many hours must be dedicated to examining countless, different telescopic fields, carefully comparing the brightness of one star against other field stars and recording those observations. As a result, Grover had to memorize the appearance of many thousands of stars strewn across the heavens. In all, he completed a survey of 14,994 stellar systems with the 6.4-inch Merz. Though not as glamorous as the work of an astronomer who discovers a new planet or comet say, Grover’s work was routine, systematic and thorough, a far cry from the limelight – the kind of assiduity that makes possible steady advances in any sphere of human enquiry. When Charles Grover was born, scarcely 40 long-­ period variable stars were known, but thanks to his efforts, dozens more were identified and studied, thereby contributing significantly to the grand corpus of astrophysical knowledge of our kind. He published much of his work annually, in some of the most prestigious journals of the age, including the JBAA and RAS. Grover’s dedication to his calling was truly prodigious. His biographer, Barbara Slater, notes, for example, that his diaries record observations carried out on 146

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nights during 1886 (in its own right serving as some measure of the true frequency of clear skies in the UK, and in sharp contradistinction to what many contemporary amateurs may claim!), including 19 nights during December, where he must have endured freezing conditions for long periods of time (indeed temperatures as low as -19C were recorded in his journals!). This author suspects that few amateurs have since endured what Charles Grover did. Like all experienced observers though, Grover’s notes reveal tantalising morsels of new insight, gained only by spending many hours at the telescope, and, often overlooked by later generations. For example, in one protracted description of the Hilger micrometer, and in connection to double star measures he writes: “A slide fitted with colored glasses allows the field to be changed to red, white or blue, at pleasure, and I have found by careful experiment that the definition of certain stars is sensibly affected by the color of light employed in their measurement.” Could Grover have discovered that the wavelength of light can affect resolving power (or ‘defining power’ as he put it)? Quite possibly yes! Certainly, this author knows of no earlier references to this phenomenon! We live in the shadow of our ancestors.

Old Age and Passing Away His employer, Sir Cuthbert Peek, died in 1901, which dealt Grover a great personal blow, as he had always held him in such high esteem. In the years after Peek’s passing, the estate was run by his son, Wilfrid. Now approaching 60  years of age, Grover’s notes reveal a growing awareness of his advancing age, but without any anxiety with the prospect of departing this world. “I never worry much about the future State,” he wrote, “for the good reason that of this we know nothing and never shall till we pass the line.” For the next 10 years, Grover continued his routine work on variable stars but also obliged visitors to Rousdon with glimpses of interesting astronomical bodies though the telescope. In 1916, tragedy struck the Grover family once again, when their only son, George, fell ill and died in London, aged 52. This was a time of great mourning for the British people in general. World War I had decimated the lives of so many families across Europe, rich and poor alike. Even the Peeks were not exempt from the specter of human tragedy. Throughout these troubled times, Charles continued to use the telescope enthusiastically, maintaining his observations whenever he could. In addition to his duties as resident astronomer at Rousdon, Grover encouraged many a young observer, writing a variety of articles for popular journals aimed at the general public. Grover’s last report on variable stars covered the year 1920 and was published by the JBAA in January 1921. On the 16th of February, Charles Grover died, just a few weeks shy of his 80th birthday.

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Fig. 21.8  Charles Grover reviewing his observing notes in his garden at Rousdon (c. 1907). (Image from http://www.steammill.phlegethon.org)

The funeral of Charles Grover was very well attended, with a long list of obituaries. The locals came out in their droves, the Peeks included, as did many men of distinction, for he counted professors and plumbers, men of titles and commoners alike as his friends. The rector who conducted the funeral service was a little lost for words, as he had only known him for 4 years. Still he recalled Grover’s quiet faith, attending service without fail every Sunday, and always seating himself at the back of the church, far from the pulpit. Grover was buried next to Sir Cuthbert Peek, his old master, whom he faithfully served and earnestly loved. Lizzy outlived her husband by 6 years and by a strange twist of fate, gave up the ghost within an hour of her master’s (Wilfrid Peek) death on October 12, 1927. Shortly thereafter, the house was sold and turned into a school. The observatory too was left to fall into disrepair and was never again used for the purposes it had been built for. The famous 6.4-inch Merz equatorial now lies in the London Science Museum, preserved for the benefit of future generations (Fig. 21.8). What better way to honor a life than to continue in his footsteps? The astronomical legacy of Charles Grover inspired others to carry on the survey of the heavens. In particular, England’s latent talent for bringing forth exceptionally gifted and dedicated variable star, comet and nova hunters continued throughout the twentieth century with the life and work of George Alcock (1912–2000), which we shall explore in a later chapter.

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An Aside: John Tebutt (1834–1916) in the New World The early sons of Australia produced their own crop of prolific amateur astronomers, no more so than John Tebbutt, son of an Englishman (John Tebutt. Sr.), who had emigrated from his native England in 1801 to begin a new life in New South Wales, Australia, a distant colony of the British Empire. After running a general store, Tebutt’s father bought a farm on land known as the Peninsula, on the Hawkesbury River, which his son inherited in 1870. Young John was educated in the local Presbyterian school administered by Rev. Matthew Adam and later completed his education under the aegis of Rev. H. T. Stiles between 1845 and 1849. It was during his school year’s that John exhibited his lifelong love of all things mechanical. And he came to regard the sky above as the ultimate mechanism of the Divine Creation. In 1853 Tebbutt purchased his first scientific instrument, a marine sextant, using it together with a clock equipped with a seconds pendulum which he regulated by making careful celestial observations. He also had a small telescope with which he projected an image of the sun. Over the next few years, Tebbutt gradually acquired more instruments and by 1863 he had constructed with his own hands a small wooden observatory on the grounds of the family farmstead at the Peninsula. On May 13, 1861, Tebbutt observed a faint nebulous object with his small marine telescope; a few days of observation showed that it was in motion and he was credited with the discovery of the great comet of 1861 (1861 II), the basic orbital characteristics of which he later computed by his own hand. By November 1861, Tebbutt added a fine 3.25-inch f/14.5 achromatic refractor to his equipment tally with which he made detailed observations of Encke’s comet (1862 I) and went on to faithfully record seven of its returns throughout the rest of his life, using ever larger telescopes. Over the years Tebbutt amassed a remarkable portfolio of observations on comets, asteroids the occultation of stars by the Moon, transits and eclipses of Jupiter’s large satellites, as well as carrying out detailed observations and measures of variable and double stars. In all, his publications numbered in the 300s. Tebbutt was also a keen amateur meteorologist, publishing extensive weather observations recorded over three decades between 1863 and 1896. In 1872 he bought a 4.5-inch (11.4-cm) Cooke equatorial refractor with which he observed the transit of Venus in 1874. In 1879 Tebbutt erected what in his words was ‘a substantial observatory of brick’ a few meters south of his old observatory and in 1886 he acquired his largest instrument, a formidable 8-inch (20-cm) aperture Grubb equatorial refractor. Tebutt was honored with many accolades from his astronomical peers. A member of the Philosophical (Royal) Society of New South Wales from 1862, Tebbutt was awarded the silver medal at the 1867 Paris Universal Exhibition for his 1871 published work ‘On the Progress and Present State of Astronomical Science in New South Wales’. In 1873 Tebbutt was elected a fellow of the Royal Astronomical Society, London, and in 1905 was awarded the Hannah Jackson, née Gwilt, bronze medal. In 1895 Tebbutt served as the first president of the New South Wales section

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of the BAA.  In his Astronomical Memoirs (Sydney, 1908) Tebbutt listed his 371 publications in various academic journals, including 120 in the Monthly Notices of the Royal Astronomical Society and a further 148 in the prestigious German periodical, Astronomische Nachrichten. In all his days he remained in Australia but ever the scholar, taught himself the other European languages; French and German in order that he could respectfully correspond with his non -English speaking astronomers. Throughout his long life, Tebbutt maintained a strong Christian faith, serving as president of the Windsor branch of the British and Foreign Bible Society. Possessing a strong moral compass, he petitioned Sir Henry Parkes in 1877 for leniency towards impoverished settlers in paying their government land dues. He died aged 82 on November 29, 1916, survived by a son and three of his six daughters.

Sources Browning, J.: A Plea for Reflectors: /books?id=Vg4JAQAAMAAJ&printsec=frontcover&source= gbs_ge_summary_r&cad=0#v=onepage&q&f=false Orchiston, W.: John Tebbutt: Rebuilding and Strengthening the Foundations of Australian Astronomy. Springer, Cham (2017) Slater, B.: The Astronomer of Rousdon. Charles Grover (1842–1921). Steam Mill Publishing, Norwich (2005)

Chapter 22

Angelo Secchi, Father of Modern Astrophysics

The Napoleonic era, which formally ended at the Congress of Vienna in 1815, brought sweeping social and political changes across Europe. Traditional values and beliefs were being questioned, as a new wave of libertarian ideas swept through Britain, France and the Italian peninsula. Politically though, the old, pre-Napoleonic status quo was once again established and for Italy, this meant Austria once again administered various states within its borders, including Lombardy and Venice. The Savoy-ruled kingdom of Sardinia recovered Nice, Piedmont, Savoy and Genoa, an important steppingstone on the journey to unify Italy, in a movement the nationalists called ‘Risorgimento’. The large division of wealth between the north and south of the Italian peninsula led to rapid urbanization and industrialization in the former, while the latter was still poor, supporting a largely underdeveloped, agrarian lifestyle. The Papal States, which occupied central Italy and the Spanish dominated Kingdom of the Two Sicilies, administered from Naples, ruled much of southern Italy, as well as the island of Sicily (Fig. 22.1). It was into this politically turbulent world that Pietro Angelo Secchi was born to middle class parents, Antonio Secchi, a joiner, and mother, Luise Belgieri, in the small city of Regio Emillia on June 18, 1818. Just a few years before, in the aftermath of the Treaty of Vienna, Reggio was returned to Francis IV d’Este, Duke of Modena, but in 1831 a revolt upwelled against him, and as a consequence, Reggio proclaimed its union with Piedmont. Despite these sweeping changes, young Angelo showed great academic promise and his parents sent him to the local gymnasium, run by the Jesuits, where he received an excellent secondary education, stoking his great passion for physical science. On November 3, 1833, the teenage Secchi enrolled in the Jesuit Order in Rome. Here he continued his education in the humanities, theology and philosophy but thoroughly excelled at mathematics and physics, so much so that by the age of 22 he was appointed tutor in physical science at the Roman College, becoming a full professor (though still without a doctorate) at the Jesuit College in Loretto by 1841.

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Fig. 22.1  Angelo Secchi (1818–1878). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Angelo_Secchi#/media/ File:Angelo_Secchi.jpg)

Despite his great gift in scientific matters, he endeavored not to neglect his theological studies, and was ordained a priest in 1847. But the security Secchi enjoyed as a young scientist and Roman Catholic priest was being eroded by fresh rumors of revolution. In 1831 Giuseppe Mazzini (1805– 1872) founded the nationalist organization, Young Italy, and by 1832 he unsuccessfully tried to induce mutiny within the Sardinian Army. Two years later another conspiracy against the Kingdom of Sardinia broke out but, once again, it ended in failure. During these desperate and politically uncertain times, Mazzini had gained considerable popularity all across Europe, so much so that he was nicknamed the ‘prophet of nationalism’. It was during the Revolution of 1848 that Mazzini finally had his day. This time, the well-organized revolt was eminently successful, with Mazzini taking his place as one of the founding fathers of the new but short lived ‘Roman Republic,’ which was to fall only a year later in 1849. The revolutionaries expressed a visceral hatred for the theocracy of the Papal States, headed by the pontiff, Pius IX (1792–1878). Secchi, together with his Jesuit colleagues, was forced to leave Rome. He travelled to Paris and then made his way across the channel to England, where he took up residence at Stonyhurst College, Lancashire, for a few months. It was during his brief time in England that Secchi lost his close friend and fellow astronomer, Francesco de Vico (1805–1848), discoverer of no less than six comets during his brief career, who sadly succumbed to an aggressive bout of typhus fever in London. On October 24, 1848, Secchi, together with twenty other exiled Jesuits, embarked on a month-long journey across the Atlantic, setting sail from Liverpool to the United States. Here he was to link up with a one Father Curley, who directed the Jesuit College at Georgetown, District of Columbia. Here he submitted and brilliantly defended his doctoral thesis and was shortly thereafter offered the post of Professor of Physics. As of yet, astronomy did not especially captivate the young

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Fig. 22.2  Portrait of Pope St. Pius X (1835–1914), 257th pope of the Roman Catholic Church. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Pope_Pius_X_ (Retouched).jpg

scientist, but that was all about to change when he stoked a friendship with the distinguished American astronomer, maritime scientist and meteorologist, Commodore Matthew Fontaine Maury (1806–1873), who was serving as the superintendent of the newly established U. S. Naval Observatory in Washington. There, Secchi published his first paper in experimental physics; on the measurement of electrical resistance and its application to telegraphy. But Secchi’s stay in the New World was to be equally short lived, when Pius IX ordered their return to Rome after the French general, Charles Odinout, terminated the Roman Republic in the summer of 1849, on the proviso that he granted religious freedom to his subjects as well as the installation of a secular government. Indeed, it was French forces that propped up Pius IX’s administration in Rome right up until the outbreak of the Franco-Prussian War in 1870 (Fig. 22.2). Anecdotally, Pope Pius IX was known for his resistance to liberalism, socialism and the separation of church and state. As the longest reigning pontiff in the history of the Roman See, he was the first to sanction the perennially controversial notion of ‘papal infallibility’, as well as the elevation of Mary, the mother of Jesus, to ‘Mediatrix’ between God and man, at the first Vatican Council (1869–70), but was eventually cut short owing to the loss of the Papal States. It would be entirely wrong however to claim that he was not a cultured man. Indeed, Pius IX was a notable patron to the religious arts, but also cultivated a keen interest in the sciences, ­particularly astronomy. Indeed, in his youth, Pius IX had taken science courses at

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Fig. 22.3  Observatory of the Roman College. (1) Main Observatory of equatorial Merz telescope. (2) Main staircase to the Observatory. (3) Observatory elliptical meridian circle of Ertel. (4) Observatory for the telescope of Cauchoix. (5) Observatory electric tower with small lead ball. (6) Antenna with globe dropped at midday as signal to fire the cannon at Castel Sant’Angelo (now on the Janiculum). (7) Electric cables transmit signals from meteorological sensors on Calandrelli Tower to meteorograf recorder housed in room below main observatory. (8) Rear of St. Ignatius facade. (9) Back of Church of St. Ignatius. (11) Tower Terrace. (12) Roof of Palazzo Montecitorio, now the Chamber of Deputies. (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/ Roman_College#/media/File:Osservatorio_del_Collegio_Romano.jpg)

Scolpian College, where he apparently submitted a detailed dissertation ‘on the construction of telescopes’. The Roman See, of course, was no stranger to the value of practical astronomy, but in the aftermath of the revolutionary years of 1848 through 1849, Pius IX was determined to set Vatican astronomical research on a new course; viz a viz, as champion of the new science of astrophysics. Indeed, it was shortly after Pius IX’s return to Rome in the spring of 1850 that he appointed Father Angelo Secchi to head the leading pontifical observatory at the Collegio Romano. It was an opportunity he found too good to refuse (Fig. 22.3). Thanks to generous private donations and direct papal support, Secchi set about building a state of the art observatory. He chose a very symbolic site for the new cathedral, dedicated to the starry heaven, the roof of the church of St. Ignatius at the Collegio Romano, set immediately above a series of imposing columns originally built to accommodate an enormous 18 meter diameter dome, but which never saw the light of day. Instead of crucifixes and statues dedicated to the saints of the

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Fig. 22.4  The 24.5-cm Merz equatorial refractor near the time of its establishment at Collegio Romana. (Image courtesy of the Armagh Planetarium)

Roman Catholic Church, Secchi would adorn the building with the finest telescopes as well as experimental electric and magnetic devices money could buy. And, all the more remarkably, he completed the construction of the building in just 1  year! (Fig. 22.4). The centerpiece of the new observatory was a fine, equatorially mounted refractor, with an aperture of 24.5 cm and a focal length of 430 cm (so f/17.6), built by the Bavarian optician, Georg Merz (1793–1867), who superseded Joseph von Fraunhofer as director of his famous optical business in Munich in the aftermath of his untimely passing in 1826. The instrument was the largest of its kind in Italy when it was finally dedicated in 1853, and truly emblematic of the fresh confidence bestowed upon a new breed of Vatican astronomers, connecting the Earth with the wider creation. As well as the large Merz refractor, Secchi, at the behest of Pius IX, also installed an elaborate meridian circle for the express purposes of synchronizing all national clocks to the Roman meridian time line. And though the Roman people were largely ignorant of the goings on inside the new Osservatorio Pontificio, they were at least grateful to the clerical astronomers for providing them with the precise time of day. The adjacent rooms leading off from the observatory were lavishly equipped with cutting edge electromagnetic gadgetry, to investigate terrestrial and solar magnetism, as well as a state of the art meteorological laboratory. A smaller Cauchoix refractor, with an aperture of 6.4 inches (16.3 cm), was also dedicated to observations of the Sun.

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Secchi’s earliest contributions to astronomy included the discovery of three new comets between the years 1852 and 1853. A decade later, he was to wade into the debate concerning the nature of fountain like jets that were seen streaming from the starlike nucleus of Comet 1862 III, proposing his fountain model to explain their nature. In effect, the jets emanating from the nucleus, in Secchi’s opinion, derived from heating of the nucleus by the Sun’s rays, the sublimating material being ejected as streamers much in the same way as geysers or water fountains. Because the Merz equatorial was fully the equivalent of the great Dorpat refractor erected in Russia, and employed by the noted German born double star observer F.G.  Wilhelm Struve (1793–1864), Secchi felt it appropriate to initiate his astronomical researches with a thorough revision of his great catalog of double stars compiled between the years 1824 and 1837. This was very exacting work that required a lot of mental concentration, but like all true science, Secchi felt that Struve’s work had to be confirmed by direct observations and measurements. After a grueling 7-year program of micrometer work at the telescope, conducted on every clear evening, Secchi was able to present the chief portion of his results in a work entitled, “Memorie del Collegio Romano” published in Rome in 1859, which contained measures of some 10,000 verified double stars. This work was later continued by his assistants in 1868 through 1875, the results of which were published in two further supplements. Indeed, the later double star astronomer, Dr. William Doberck (1852–1941), extensively leaned on Secchi’s catalog (as well as other historical measures) in deriving many of his orbital calculations. Secchi carried out many routine observations of the planets, particularly Mars, Jupiter and Saturn, the great telescope producing beautiful and highly detailed images of these worlds in the tranquil Roman air. He conducted accurate micrometer measures of the size of the Jovian disk and identified essentially all of the features in the planet’s atmosphere that are enjoyed by modern medium aperture telescopes, including many of the belts and zones, ovals, barges, as well as the Great Red Spot (or ‘hollow’ as it was then known), and speculated on whether the asymmetry he observed in the equatorial bands provided any deeper clues as to the nature of this giant planet. He also studied the kinematics of Jupiter’s four large moons, as well as producing, through prolonged observations with the 24.5-cm Merz, a highly detailed map of the large lunar crater, Copernicus. Secchi conducted many detailed observations of Mars with the 24.5-cm Merz refractor, identifying the dark areas as extensive ‘seas’ and the lighter areas as ‘deserts,’ much in the tradition of his contemporaries. According to E. M. Antoniadi, Father Secchi was the first observer to correctly identify giant dust clouds on the planet as early as 1858. And while many historians of the planet Mars attribute the origin of the concept of ‘canali’ to the ruminations of G. V. Schiaparelli, it was actually an idea coined by Secchi’s fecund mind, who indeed recorded canal-like structures on the planet’s surface, though they were not as ‘linearized’ as those depicted by his Milanese compatriot. Secchi’s theology, which still seems little differentiated from the contemporary Jesuit astronomers; took him far beyond the authority of the Bible, and allowed him to openly accept that ‘reality’ of the plurality of habitable worlds: “In our opinion, “Secchi wrote, “it seems absurd to regard the vast regions

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[of the universe] as hardly inhabited deserts; rather, they must be richly populated with beings intelligent and rational, capable of knowing, honouring and loving their Creator.” Such unbridled speculation was typical of men of his day, but, as modern science is continually revealing (or rather not revealing!) the question of the ‘inevitability’ of life on other worlds is not at all as certain as it seemed only a few decades ago. Nor had he any idea of just how astonishingly complex even the simplest living systems are. Much of Secchi’s work on planetary astronomy may be consulted in his highly influential 1859 publication, “Il quadro fisico del sistema solare secondo le pill recenti osservazioni.” 1859 proved to be a very important year in the history of science for an entirely different reason. At the University of Heidelberg the chemist Robert Bunsen and physicist, Gutav R. Kirchoff showed that there were clear connections between the dark Fraunhofer lines first detected in the solar spectrum back in 1814 and particular chemical elements. Specifically, when sunlight was admitted through a spectroscope, some of the dark lines seen corresponded with bright lines from incandescent elements, suggesting that the spectral lines were actually signatures of elements making up the incandescent material. Kirchoff further proposed a model that would explain the many dark lines in the solar spectrum. The Sun’s atmosphere, Kirchoff surmised, absorbed energy at particular wavelengths producing a so-called ‘absorption spectrum.’ When no absorbing gas was present, the elements gave off ‘emission’ lines. News of the novel science of spectroscopy soon reached the ears of a well-to-do Londoner, William Huggins (1824–1910), who in the mid-1850s had set up a private observatory at Tulse Hill, south London, where he lived with his elderly parents. Befriending William Rutter Dawes, in 1858 Huggins purchased from him a fine 8 inch doublet achromatic objective by Alvan Clark, and mounted it in a tube made by Thomas Cooke & Sons of York. News of the discovery by Bunsen and Kirchoff electrified the 36 year-old Englishman who later likened it to a ‘spring of water in dry and thirsty land.’ With the help of another acquaintance, Professor William Allen Miller, based at Kings College, London, Huggins devised spectroscopes for use with the 8-inch refractor and conducted a series of experiments with 24 commonly available elements, producing simple spectra of them so that he could link these to what he saw in stellar spectra. Over the next 5 years, Huggins had produced a variety of telescopic and laboratory derived spectra the first of which was published by the Royal Society in 1864. This early work showed that there were great similarities between the spectra of stars and that of the Sun. But it was also in 1864 that Huggins made a spectroscopic discovery that would shine considerable light into the nature of nebulae which had refused to resolve into stellar bodies using even the largest telescopes in the world. In particular, when Huggins turned his astronomical spectroscope on the Cat’s Eye Nebula in Draco, he did not see the usual forest of spectral lines seen in the stellar spectra but rather few singled out lines that did not appear to correspond to any known element on Earth. He thus tentatively called the ‘new’ element ‘nebulium’

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(although these lines were later shown to be generated by ionized oxygen and nitrogen atoms). By the end of 1864, Huggins had found a half-dozen examples of these gaseous nebulae. This raised all sorts of new questions in the mind of Huggins; could these spectra reveal real characteristics of the physical composition of the heavenly bodies? And since the work of the Austrian physicist, Christian Doppler (1803–1853) showed since 1841 that the properties of sound waves could be used to determine whether they were either receding or approaching us at speed, Huggins wondered whether the same analysis could be applied to light. If the celestial object was receding from us, it ought to generate a so called redshift (with a given line transposed to a longer wavelength) or blue shift, as the object moved towards us. By 1868 Huggins managed to calculate from his spectral observations of Sirius that it was receding from us at the colossal speed of 29.4 miles per second (a figure he later refined). Across the Atlantic in America, other grand amateurs were trying their hand at the new science of spectroscopy. Henry Draper (1837–1882), the son of an English physician who had emigrated to Virginia in 1837, developed a keen interest in astronomy after visiting the great 72-inch Leviathan of Parsonstown, Ireland, in the mid-1850s. After his return to New York, Draper tried his hands at constructing a 15-inch aperture speculum metal Newtonian but was unable to give it the required shape to render good images. But after receiving sound advice from his correspondences with Sir John Herschel, decided to switch to silver on glass mirrors for his telescope optics. This time he was successful, fashioning a suite of increasingly large glass mirrors, culminating with an excellent 28-inch reflector, which he completed in 1872. Draper’s training in medicine (following in his father’s footsteps) also familiarized him with practical chemistry skills, which led him to explore the new science of photography, and in particular, its application to astronomy. By this time, Draper had married a lady of considerable means, Anna Mary Palmer, which allowed him to retire his medical practice and devote himself entirely to astronomy. At their luxurious home in Madison Avenue, New  York City, the Drapers set up a state-of-the-art astrophysical laboratory combining the spectroscope with the photographic plate. In 1872, Draper managed to produce the first photographic spectrum of the bright star Vega using the formidable light gathering power of his 28 inch telescope. Draper was also the first astronomer to obtain high quality images of selected deep sky objects. For example, by 1880 he had successfully recorded an excellent image of the Orion Nebula, revealing stars as faint as the 14th magnitude. Thus, while Secchi was strictly a professional astronomer, much astrophysical progress was made by amateurs who had the means to conduct the work. Secchi developed a particularly intense interest in solar astronomy, employing the 6.4-inch Cauchoix refractor to make daily drawings of the white light solar disk. Any interesting sunspots, faculae and prominences were scrutinized very closely and recorded with exquisitely fine drawings made at the telescope. Secchi, together with some of his research assistants, transported the 6.4-inch equatorial to Spain to observe the total solar eclipse of July 18, 1860, where he was to photograph the solar corona and prominences thereby silencing any skeptics who had previously claimed that such phenomena were entirely illusory and/or were associated with

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some kind of lunar structure. Just one month later, Secchi was electrified to hear of the progress of Pierre Jules Janssen (and independently by Sir Norman Lockyer in England), who had manipulated the spectroscope to observe such prominences during broad daylight. Indeed, it was the spectroscope that enabled Secchi to make his unique mark in stellar astrophysics; by convincingly demonstrating that not all stars have the same composition. On his return from the expedition to Spain, Secchi commissioned the instrument makers Hoffmann and Merz to build special spectroscopes with multiple prisms, as well as an ingenious objective prism that would enable him to observe multiple stellar spectra simultaneously. When coupled to the long, native focal length of his observatory refractors, Secchi was able to obtain images of sufficiently large image scale to study these spectra quite well through entirely visual means! This epochal work began in 1862 culminating 5 years later in 1867 with a stellar classification scheme including more than 4000 stars, which he divided into five distinct categories: Type I: Appearing white or blue white through the telescope, characterized by broad, heavy hydrogen lines. A subclass showed narrower lines. This type includes the modern class A, B and early class F. These include familiar luminaries such as, Vega, Rigel and Altair. Type II: The yellow stars showing weakened hydrogen lines, but with the addition of metallic lines. This type includes what astronomers recognize today as late class F, G and K stars. Type III: Looking orange or red to the eye, these show complex band spectra, and include familiar stars like Betelgeuse and Antares. Secchi’s third type corresponds to the modern class M stellar category. Type IV: The intensely red stars (C and M class subtype), with strong absorption lines owing to carbon and its simpler molecules. Secchi was mesmerized by this class of star as they showed very clear differences in chemical composition to the earlier types. So taken was he by the beautiful appearance of the spectrum of one member, Y Canum Venaticorum, that he nicknamed it La Superba, a time honored moniker among astronomers. Type V: These show strong emission lines and include γ Cassiopeiae and β Lyrae. It is all the more remarkable that Secchi achieved so much given the fact that the objective prism he employed with the large Merz equatorial effectively reduced its aperture to about half of its working diameter (so about 5 inches in reality)! Furthermore, the significant additional mass incurred in carrying the prism led to problems with the tracking of the equatorial mount, which would have undoubtedly frustrated any efforts made to record those faint spectra. It is also easy to underestimate the achievements of Secchi in providing the first break down of the various stellar classes of stars, for it represented the first step toward understanding how stars evolve in time. In 1865, the Leipzig based astronomer, Friedrich Zöllner (1834–1882), suggested that stars were first born hot, and, as they naturally cooled, passed through the solar type to the more highly evolved red stars. However, it was another Leipzig born astrophysicist, H.C Vogel (1841–1907),

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Fig. 22.5  Herman Carl Vogel (1841–1907). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Vogel_Hermann_Carl. jpg)

based at Potsdam Observatory, Germany, who greatly advanced the cause of stellar spectroscopy beyond the virginal efforts of Secchi (Fig. 22.5). Working in collaboration with the Swedish astronomer, Nils Christofer Dunér(1839–1914), who also employed a 24.5-cm Merz achromatic refractor at Lund, he prepared catalogs of stellar spectra of tens of thousands of stars. It was Vogel’s classification scheme that led to the idea of an orderly evolutionary progression between the various star types; an idea that found its fullest expression in the Hertzsprung-Russell diagram, so central to modern stellar astrophysics (Fig. 22.6). Secchi had reached the height of his career in the midst of social and political upheaval. Italy’s unification was finally accomplished by the leadership of two men, Camillo Benso, Count of Cavour (1810–1861) and Giuseppe Garibaldi (1807– 1882), but not without considerable help from foreign agencies. In 1858, Cavour brokered a deal with France. Specifically, Cavour, who administered Piedmont, agreed to bequeath France some of its territory in return for its military assistance in ousting the Austrian forces, who were controlling most of Italy at the time. Two years later, Garibaldi raised a volunteer army to complete the cause of Italian unity. He conquered much of Southern Italy in a bloody civil war, after which time Cavour’s armies were amalgamated with his own forces, pacifying much of the peninsula and establishing the nation of Italy in 1861. The final cementing of Italian unity came from the aid of Prussia, which formed a military alliance with Italy in the wars of 1866 and 1870, defeating France and Austria and ordering the expulsions of all their politicians and administrators by 1870. Italy as we now know it, was finally born, and with it, came the dissolution of the papal states. From the outset, the new Italian government was keen to foment its newfound unity in all matters, including science and technology. Accordingly, Secchi was invited to accompany a team of astronomers, physicists and technicians from all over Italy to observe the total solar eclipse from the island of Sicily, which was to take place on December 22, 1870. The expedition was to include scientists from

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Fig. 22.6  An observational Hertzsprung-Russell diagram with 22,000 stars plotted from the Hipparcos catalog and 1000 from the Gliese catalog of nearby stars. Stars tend to fall only into certain regions of the diagram. The most prominent is the diagonal, going from the upper-left (hot and bright) to the lower-right (cooler and less bright), called the main sequence. In the lower-left is where white dwarfs are found, and above the main sequence are the subgiants, giants and supergiants. The Sun is found on the main sequence at luminosity 1 (absolute magnitude 4.8) and B-V color index 0.66 (temperature 5780 K, spectral type G2V). (Image courtesy of Wiki Commons. https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram#/media/ File:HRDiagram.png)

Rome, Florence, Naples, Padua and Palermo, the capital of Sicily. Intriguingly, Secchi, though eminently qualified to do so, was not given any overarching authority over the rest of the scientific team, perhaps, as some scholars have suggested, to express the egalitarian values of the ‘New Order’ That said, Father Secchi, in the true spirit of open scientific enquiry, enthusiastically agreed to go. This was by far the most ambitious and centrally organized scientific endeavor ever mounted by the newly minted Italian nation. But it was not without its perils;

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the Italian army had to accompany the scientists as they transported their telescopes, chronographs and photographic plates across the island, all the while wielding the new national flag, as hostility was expected from the islanders who, as recently as 1866, had mounted an anti-Italian insurrection. They were also accompanied by independent British and American expeditions, headed by Sir Norman Lockyer and Professor Charles Augustus Young, respectively. The scientific program included visual and spectroscopic observations of the solar corona and prominences, with Secchi overseeing the photographic projects. Though the weather proved to be rather cloudy and the photographs turning out poor during the course of the eclipse, Secchi was able to obtain spectral evidence of an entirely new solar phenomenon known as a flash spectrum, immediately above the photosphere, which was also confirmed by the American astronomers. Secchi was keen to standardize the observations of all the Italian observers and, having set up his small Merz refractor in situ, instructed them to take their turns making visual sketches of the prominences they saw at the eyepiece. The learned Padre was apparently quite taken aback by the large variations exhibited in their drawings. Some saw things that were apparently quite invisible to others, which only serves to endorse the old adage that a single trained eye is better than a dozen untrained ones! Yet in other ways, Secchi was the instigator of exceptionally high standards in the co-ordination of astronomical observations. His working knowledge of electromagnetism enabled him to set up near simultaneous communications with his fellow astronomers across the continent of Europe in order to compare their observations with those made at Sicily. Indeed, over the next few years, together with his friend and fellow astronomer, Pietro Tacchini (1838–1905), he established an elaborate observation network with other Italian astronomers so that they could compare spectroscopic analyses of the Sun at almost the same time every day. Indeed, Secchi’s standardization methods were soon adopted by all major centers of international astronomy. It was Tacchini’s loyalty to Secchi that probably secured his future appointment as the Director of Research at the Observatorio del Collegio Romano after Secchi’s passing. Secchi’s intense researches into the physics of the Sun provided us with an essentially modern conception of the makeup of our star. Perhaps more clearly than anyone who ever lived before him, Secchi understood that the Sun is a star like myriad others that grace the cosmos. He believed that sunspots were regions of increased magnetic activity and that the various prominences he observed on the solar limb influenced terrestrial weather. He also correctly deduced the gross structure of the Sun, with a superhot and dense core overlaid by a progressively cooler gaseous atmosphere. His influential solar monograph summarizing his ideas, Le Soleil, was first published in Paris in 1870, followed up by a German translation which first appeared in 1872 and a second French edition appeared in 1875. Secchi believed Earth and the universe to be very old; tens of millions of years, if not more. This seemed to be endorsed by new theoretical work conducted by some of the finest theorists of his age, particularly William Thomson (Lord Kelvin) (1824–1907) and Hermann von Helmholtz (1821–1894), who had proposed a mechanism of slow gravitational contraction as the process that powered the Sun

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over these timescales. And though this was superseded by the theory of thermonuclear fusion in the twentieth century, it is still a valid process in the formation of protostars, as well as the evolution of aging stars off the main sequence into giants. Collectively, these new scientific revelations served only to deepen Secchi’s faith in a great Creator God, who upheld the workings of a unified Universe, with all its matter and motion, through His Logos. In the closing years of his life, his devotion to the Jesuit Order in general, and to the Holy Father in particular, continued to cause tensions with the secular Italian government, which had placed restrictions on Jesuit teachings and research in Rome and farther afield. Secchi was offered the chair in physical astronomy at the University of Rome, which initially he accepted, on the condition that the Jesuits be allowed to continue their ambitious program of education and scientific research. When they refused, Secchi withdrew his offer. By 1872, the Italian government formally protested against Secchi’s representing the Roman Catholic Church at the prestigious Commission Internationale du Metre held in Paris, which they evidently saw as confusing the role of church and state. In 1873, the Collegio Romano was declared the official property of the Italian government. And by 1874, to add insult to injury, the same government severed all ties with Secchi by dispatching a team of Italian astronomers to India to observe the transit of Venus entirely without his consultation. It was a bitter blow to the diligent Jesuit scientist, who had doggedly refused to pledge his allegiance to the new nation instead of the Pope. Over the next few years, his health gradually failed and eventually he succumbed to a mystery stomach ailment on February 26, 1878, aged 59 years; and less than 3 weeks after his great patron, Pius IX, passed away (Fig. 22.7). Secchi received many honors from fellow astronomers outside Italy. He was elected to England’s prestigious Royal Society and Royal Astronomical Society, the French Académie des Sciences, as well as Russia’s Imperial Academy of St. Petersburg. A lunar and Martian crater were also named in his honor, as well as the asteroid 4705 Secchi, residing in the main belt. Outside the sphere of astronomy, Secchi’s name is associated with many other fields of scientific enquiry. One example is the Secchi disk, a simple device devised by him in 1865, which is used to assess the turbidity of sea and fresh water reservoirs. The disk, which has a diameter of 30 cm, is usually mounted on a pole or line, and slowly lowered down into the water. The depth at which the disk is no longer visible is taken as a measure of the transparency of the water. Such an ingenious device was first used by oceanographers in the Mediterranean Sea, but nowadays it is employed almost universally in slightly different forms. As father of modern astrophysics, Secchi’s legacy was carried into the twenty-­ first century when the Solar Terrestrial Relations Observatory (STEREO), which entered orbit in 2006, carried on board a suite of instruments known collectively as the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI), in remembrance of the great nineteenth century Italian astronomer. Finally, it is worth noting that Secchi founded a dynasty of Jesuit astronomers that continue to bring the heavens closer to the Earth, even to this day.

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Fig. 22.7  Bust of Angelo Secchi by Giuseppe Prinzi as it appears in the gardens of the Pincio Hill, Rome (Image courtesy of Lalupa). (Image courtesy of Wiki Commons. https://en.wikipedia.org/ wiki/Angelo_Secchi#/media/File:Pincio_-_Secchi_1010971.JPG)

Sources Antoniadi, E.M.: The Planet Mars. Keith Reid Limited, Shaldon (1975) Aubin, D., et al. (eds.): The Heavens on Earth. Duke University Press, Durham (2010) Chapman, A.: The Victorian Amateur Astronomer. Leominister/Herefordshire, Gracewing (2017) Hearnshaw, J.B.: The Analysis of Starlight: Two Centuries of Astronomical Spectroscopy. Cambridge University Press, New York (2014) Secchi, A.: A biography. http://www.newadvent.org/cathen/13669a.htm

Chapter 23

John Birmingham, T. H. E. C. Espin and the Search for Red Stars

Anno Domini 1866. The Leviathan of Parsonstown, with its 6-foot primary mirror, reigns as the largest telescope in the world, bringing international prestige to Irish astronomical science, and both Dublin and Armagh have well established observatories that date back to the end of the eighteenth century. Their administrators are formally trained, their observing programs, specialized. But far from the Irish cities, west of the great Shannon River, a 50-year-old gentleman, hitherto unknown to the astronomical community, was strolling home along a narrow dirt road that wound its way north from the small town of Tuam, County Galway. It was shortly before midnight on the evening of May 12 that he saw a second magnitude star he had never noticed before in the constellation of the Northern Crown, then situated very high in the sky. After reaching his home at Millbrook House, he sat down by the light of a paraffin lamp to check the star charts in his library. To his amazement, the only star recorded in the position he estimated was of the 9th magnitude, far too faint for even his keen eyes. He had just discovered the brightest nova to grace our skies since 1604; the star T Coronae Borealis! (Fig. 23.1). Such was the meteoric arrival of John Birmingham (1816–1884) upon the world’s stage; an accomplished poet, land owner and man of letters. John was born the son and only child of Edward Birmingham and Elly Bell, who set up home at Millbrook House, near the village of Milltown, from which they received a comfortable income as landlords of a small landholding, itself part of the greater Millbrook Estate. John was educated at St. Jarlath’s College in the nearby town of Tuam and grew up to become a fine figure of a lad, both stronger and taller than many of his peers. Though there is no evidence that he attended university, we may infer from his lifelong interest in scientific matters, particularly geology, as well as his noted ability as a writer, he received an excellent and well balanced education, acquiring significant scientific knowledge from the greater popularizers of his day. Records do show however, that he was actively involved in famine relief during the years 1846 and 1847, which claimed the lives of a million people; about one eighth of the population; from starvation or the associated epidemic disease that swept the nation

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Fig. 23.1  The brilliant red giant star, Betelgeuse, shining in the northern winter sky. (Image by the author)

between 1846 and 1851. Another two million souls emigrated in a period of a little more than a decade (1845–1855). Birmingham spent about 6  years traveling through Europe in the late 1840s through to the mid-1850s, learning the language and culture of the nations he visited, and spending the majority of his time in Berlin, where he eked out a living from the circulation of interesting scientific articles for popular journals and newspapers, often writing under a pen name. It was here also that historians suggest he had his first encounter with the astronomical world. In particular, he took a great interest in the work of the famous German astronomer, Johann Franz Encke (1791–1865), with whom he established a strong bond of friendship. Birmingham returned to his ancestral home in the late 1850s, ostensibly acquainted with the language and literature of the French and German tongues. The skies in this part of Ireland were often overcast and dominated by weather systems rolling in from the nearby Atlantic, but on clear evenings, the sky would have been gloriously dark and wonderfully transparent, purged of dust and other particulates; skies that would have commanded a visceral sense of awe and wonder in the young Irishman. By all accounts, his earliest astronomical equipment was very modest; most likely a small spyglass delivering a fixed magnification of 23x, but it is clear from his later discovery that he cultivated an excellent knowledge of the naked eye heavens. The apparition of Donati’s Comet in 1858 and the Great Comet of 1861 induced great excitement in Birmingham, penning a string of prize winning essays on their appearance and significance; works which appeared in some of the most prominent British and Irish newspapers of the time. But his political connections raised eyebrows among some members of the Imperial establishment. The silver–tongued

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Birmingham was a patriot and associated with British politicians who were sympathetic to the cause of Irish independence. Perhaps the latter fact helps to illuminate the bizarre way in which the discovery of the eruptive variable star was made known to the outside world. In the wee small hours of May 13, Birmingham drafted a letter to the editor of the London Times and promptly dispatched it. It landed in his hands just a few days later, who, after reading it, promptly discarded it in a waste paper basket! When no acknowledgement was received by Birmingham, he decided to bypass the standard modus operandi of contacting the observatories at Dunsink and Greenwich, and instead wrote of his discovery to one of the most accomplished and respected British astronomers of his day; William Huggins (1824–1910), pioneer in astronomical spectroscopy, who ran a very well equipped private observatory from his home at Tulse Hill, London. This time it was well received, and Huggins enthusiastically turned his spectroscope toward it on the evening of May 18, finding it to be quite unlike anything he had ever seen before! A normal stellar spectrum presents as a streak of colors as in a rainbow, with faint dark lines. The spectrum of T Coronae Borealis, on the other hand, presented with very bright emission lines thought to be due to superhot hydrogen gas. Indeed, Huggins believed that the star had ejected a shell of excitable matter (Fig. 23.2).

Fig. 23.2  Sir William Huggins (1824–1910), a portrait by John Collier. (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ File:Sir_William_ Huggins_by_John_Collier. jpg)

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Birmingham also wrote to his local newspaper, providing details of his discovery: I discovered it on the night of the 12th instant, when it appeared the 2nd magnitude, rather more brilliant than Alpha of the above constellation, with a bluish tinge, forming nearly a right angled triangle with Delta and Epsilon. It had nothing whatever of a cometary aspect. The state of the atmosphere prevented my seeing it again until the 17th, when it appeared reduced to the 4th magnitude….

It was Huggins who endorsed Birmingham’s discovery at a later meeting of the Royal Astronomical Society and, after word of his discovery spread throughout Europe, the German astronomer, Julius Schmidt, based at Athens, was able to confirm, by the consultation of his notebooks, that only hours before Birmingham noticed the brightening of T Coronae Borealis, the star appeared as it normally did, i.e., a faint field object in his 6-inch equatorial refractor. Indeed, Schmidt named a lunar crater after the Irishman, located near the Moon’s northern limb, presenting it in his famous map, which was first published in 1878. The discovery of T Coronae Borealis dramatically changed the course of Birmingham’s life and from then on, he dedicated himself to further astronomical observations. Realizing that his existing equipment was not really up to the task of doing any serious telescopic work, he set about acquiring a suitably powerful instrument. Huggins had enthusiastically assisted Birmingham in his telescopic researches, warmly recommending that he acquire a moderate-sized Cooke refractor for the purposes of continuing his work. Indeed, we know that Birmingham had visited some acquaintances at Scarborough, a seaside town not far from where Thomas Cooke & Sons of York had set up their world renowned telescope-making workshops. The instrument he finally acquired in 1869 was a fine 4.5-inch f/15 achromatic doublet, purchased for the princely sum of £120 (still a very large sum by Birmingham’s standards). Curiously, the object glass of the telescope was rumored to have been made by Howard Grubb of Dublin. But what, pray tell, would he employ this quality telescope to do exactly? This became ever more clear by the opening years of the 1870s, after he struck up a correspondence with one of the great amateur astronomers of his age; the Reverend T. W. Webb, who suggested that he take up the task of hunting down and cataloging the positions and magnitudes of red and orange stars, some of which would be variable, a project that was only partially addressed in earlier decades by Sir John Herschel (1792–1871) and the celebrated binary star observer, Friedrich Wilhelm Struve (1793–1864), in addition to the Danish astronomer, Hans Schjellerup (1827– 1887), who compiled a list of 280 red stars published in 1866  in Astronomishe Nachricten. His 4.5-inch aperture, long focus achromat would be able to reach stars down to the 12th degree of glory, and with a special, low power eyepiece delivering a power of 53 diameters, he would be able to scan (fairly) large fields of sky. So, the middle-aged amateur from the wilds of the Emerald Isle set about his new avenue of astronomical enquiry; a task he enthusiastically embraced with both hands! (Fig. 23.3).

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Fig. 23.3  Tiberius, the author’s 5-inch f/12 classical refractor; a very similar instrument to that employed by John Birmingham, and used for the purposes of reconstructive history. (Image by the author)

Birmingham devoted the next 4 years of his life searching the sky for red and orange stars. His copious notes show that he would often begin after supper and work all the way through until dawn, weather permitting. Such devotion reflected, at least in part, his bachelor status. He never married and is rumored to have fathered a child (female). He was acutely aware of the rather subjective nature of accurately assigning colors to the stars he observed. In particular, his continual correspondence with Webb alerted him to the inherent weakness of the refractor in revealing the true color of stellar bodies and how the new silver on glass Newtonian reflectors, with their perfect achromaticity in comparison to the former, might be better tools for carrying out such delicate work. We do know however, that Birmingham had the presence of mind to include, where possible, relevant comments from other observers who, at his request, had examined the same stars. He also estimated their brightness in comparison to other field stars. Most of the stars he listed were brighter than magnitude +10 but quite a few were as faint as magnitude 12. During the course of his surveys, Birmingham became intensely interested in the spectroscopic work of Father Angelo Secchi, who had himself collated a list of over 400 colored stars in 1872 and had begun to subdivide stars into five spectroscopic types. It was during these years that the concept of stellar evolution was first enter-

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tained, an idea that greatly appealed to Birmingham and which provided further impetus to continue his surveys. While compiling his list Birmingham included Secchi’s available spectral data with his visual notes. Birmingham’s work culminated in a list of 658 orange and red stars, published under the title: The red stars: Observations and catalogue, which he presented to the Royal Irish Academy on June 26, 1876. The work was enthusiastically accepted and published in August 1877. It is clear from the work that he owed an especial debt to Webb, who had examined about 80 of the stars in his catalog and provided his own notes on their color and brightness. Birmingham was also generous to a fault in providing full acknowledgements to all other collaborators. The red stars also contains very interesting speculations concerning the nature of variables; how and why they brightened and faded. He had himself noted subtle changes in the color of red variables. In particular, their color often became paler to his eye as they brightened and deepened in hue before fading back. This suggested to him that such stars were not dying, as many of his contemporaries held. He also dismissed the idea that the variation in such stars was due to stellar rotation. Birmingham offered his own explanation, which, in his own words, involved, “the intervention and recession of a nebulous belt around the star.” Taking inspiration from the reddening of the Sun as it approached the horizon (what we refer to today as Rayleigh scattering), Birmingham believed an annulus of dusty material of varied density forming around such stars could cause them to dim and brighten with regular periodicity. Birmingham was the first observer to note that red variable stars were unevenly distributed in the heavens, being more highly concentrated in a large patch of Northern Milky Way encompassing Lyra, Cygnus and Aquila; a swathe of sky he referred to as the “Red Region.” In the years after the publication of his catalog, Birmingham became increasingly involved in the spectroscopic designations made by his peers across Europe. For example, he queried Secchi’s assignment of the newly discovered Wolf-Rayet stars to Type IV, and was rather annoyed when the Roman Padre expressed his skepticism that there really existed a concentration of such stars in certain regions of the sky. John’s original work provided fertile ground for other observers to carry out new surveys for red stars. Indeed, Birmingham issued two voluminous addenda featuring a new list compiled by the astronomer, Carl Frederik Fearnley, and another taken from the double star lists of Struve and Herschel. In the last years of his life, Mr. Birmingham continued to search the skies for more red stars with his 4.5-inch refractor and discovered yet another red star in Cygnus in 1881. He continually updated his list with new spectral data which was streaming in from observers on the continent. In the last year of his life, the Royal Irish Academy, convening at Dawson Street, Dublin, presented Birmingham with its prestigious Cunningham Gold Medal on January 14, 1884 for his distinguished astronomical career. Its President, the poet Sir Samuel Ferguson, honored him with these words: If I might express an individual opinion I would say that…..you content yourself with noting facts; and shunning plausible but doubtful methods of accounting for them. It is thus [that] solid knowledge is ultimately attained to. Of you let it be said, itur ad astra. Proceed, with

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the best wishes of the Academy, in your philosophic method, and bear back with you to the Bermingham country this medal, as a token and assurance to our brethern beyond the Shannon that wherever Irishmen devote their leisure to higher learning, there exists for them here, in the capital of their own part of the United Kingdom, a body having perpetual succession, and speaking with the voice of the constituted authority, whose business it is to sympathise with them, to encourage and reward.

This was but one of many accolades delivered to the Tuam astronomer but they were ultimately powerless to change the personal circumstances of his life. The Irish Land League was established with the primary aim to abolish landlordism in Ireland altogether, and to enable tenant farmers to own the land they worked on. As a result, many of the tenants paying rent to Birmingham refused to do so. In addition, he had to fight a succession of legal threats to the title of both his lands and his house. Collectively, these events left him seriously short of money, which resulted in his slump into poverty. Indeed, one of his own tenants described the desperate state of his last days; “he [Mr. Birmingham] was all spent up and starved with the hunger.” He passed away in the early hours of September 7 1884, aged 68 years. In the aftermath of his death, Birmingham’s house and estate were ransacked and rendered derelict, with much of his written notes and books burned or left to the elements. And what remains of Millbrook House is a but a ruin to this day. Only his wonderful telescope survived, which was preserved for many years at his alma mater, at St. Jarlath’s College, before being handed over to the Milltown Community Museum for posterity. And yet, all the while, Birmingham’s work was not done in vain, for it was to be taken up once more by a most eccentric Anglican clergyman: Thomas Henry Espinell Compton (T. H. E. C.) Espin (1858–1934) who, with singular enthusiam, greatly advanced the story of the red stars. Espin, the only child of the Reverend Thomas Espin, chancellor of the diocese of Chester, was born in the city of Birmingham on May 28 1858. At age 14, Espin entered the elite boarding school for boys at Haileybury, where his headmaster, himself an astronomy enthusiast, encouraged and instructed his pupils in basic astronomical knowledge. It was the appearance of Coggia’s Comet in the sky in 1874 that really stoked his interest in all things celestial. From 1876 to 1878, he was sent to France to complete his secondary education before going on to Exeter College, Oxford University in 1878 to read theology, for which he obtained a good honors degree. Here, his interest in astronomy flourished further when the Savilian Professor at Oxford, Charles Pritchard, allowed him to use the 13-inch De La Rue reflector of 10-foot focus at the University on the condition that he provide practical instruction to other students. It was an offer Espin could not refuse. And he excelled at what he did best; filling curious newcomers with a sense of wonder and awe for the Universe, as revealed by the telescope. By January 11, 1878, aged just 20, he was elected a Fellow of the Royal Astronomical Society (FRAS) during the presidency of Sir William Huggins. On leaving the University, Espin took holy orders, following his father into a clerical career in the Anglican Communion, accepting curate positions first at West Kirkby, Wallasey and Wolsingham in 1881, 1883 and 1885, respectively, before

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finally taking up permanent residence as Vicar of Tow Law, County Durham, in 1888; a post he was to retain for the rest of his life. In 1880, while at Wallasey Rectory, Birkenhead, Espin wrote to the English Mechanic, proposing the formation of an amateur society aimed at organizing and coordinating observations and that the best way to do so was to arrange meetings where local amateurs could discuss their observations in an open and congenial manner. The following year, 1881, the Liverpool Astronomical Society was founded. After inheriting his father’s estate, he became financially independent, allowing him to pursue many avenues of independent scientific research, much in the same vein as Birmingham before him, including geology, botany and photography. He was an avid student of paleontology, amassing an impressive variety of fossils during his long career; a study that led him to firmly conclude that Darwin’s theory of evolution was false. He was also a keen microscopist, with an encyclopedic knowledge of cell biology and the behavior of Protozoa. Intriguingly, Espin was one of the earliest pioneers in the study of X-rays, and enjoyed using his parishioners as ‘guinea pigs’ in his early experiments! Espin regarded his vicarage as an ‘open house’ that could be visited any time by his parishioners. They must have been fascinated by his vast collections of books, plants, rocks, fossils and aquaria to cultivate his ‘animalcules’ and pond weed for the microscope. After all, he was, like John Birmingham also, a life-long bachelor. In his garden, he established a small sanatorium in order to provide his sickly ‘flock’ with some relief from the consumption (Tuberculosis). He turned the basement of his home into a gymnasium and even set up a rifle range on his grounds for use by the parish ‘lads.’ He provided funds to construct a new spire for his church. All of this was done at the expense of not providing the traditional pastoral care for his parishioners though; he didn’t do house visits, refused to set up a parochial church council and would not admit women into his choir. And to top it all off, he was a well-traveled gentlemen and a formidable Biblical scholar. As a boy, Espin explored the heavens using opera glasses and enjoyed a 1 inch aperture Dollond refractor as his first telescope. By the time he entered Oxford University, he had progressed to using a 3-inch refractor for his own recreation. Sometime later, Espin was presented with a 5-inch refractor by the head of the Harrison line of steamers, a Churchwarden at his old parish of Wallasey, which he also used to good effect. While at Wolsingham, Espin set up his first makeshift observatory using the 5-inch refractor and made regular observations through it until he secured his permanent post at Tow Law. As Webb’s right-hand man, Espin assisted his famous ‘elder statesman’ in several revisions of his celebrated Celestial Objects for Common Telescopes. And it was also Webb who piqued Espin’s interest in a fabulous new line of reflecting telescopes being fashioned by master opticians such as George Calver and George With. With these novel instruments, he was able to carve out his own unique legacy in the annals of astronomical history. Their generous apertures, much lower cost than traditional refractors, as well as their freedom from chromatic aberration, made them a very popular choice for a new generation of amateur and professional astron-

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omers alike. And it was Webb himself who spearheaded this movement across Britain! We shall not dwell on the historical evidence supporting the above assertion, for this will be covered far more extensively in a separate chapter of the book. That said, in the following excerpt, which is part of a written correspondence between Webb and a one Arthur Raynard, we gain a glimpse of his evangelism for the new silver on glass specula: It might be worth your while to consider, before finally deciding, the comparative merits of the silvered glass reflector. You have probably heard of this beautiful instrument…. At present it is only in the hands of amateur makers, but their success has been remarkable. One of at least 8 inches clear aperture may be purchased in Hereford for about £26 or £27. As far as looks go, it is certainly very common and clumsy looking affair – being merely a great square tube of stained deal, mounted on a plain wooden stand – and if you regard appearances I could not say much for it. But the Newtonian reflector, under any circumstances, is a singular looking instrument.

Webb had himself proven the worth of these new instruments, acquiring a string of silvered mirrors and complete telescopes. Indeed, according to the noted British double star observer, Robert Argyle, they were able to resolve double stars well below 1 second of arc: “The 9 1/3 inch With Berthon reflector was obviously of high quality. One of the regular test objects used by With and Calver was γ2 Andromedae. The 8.5-inch mirrors of both makers were guaranteed to divide the pair, at a time when the separation was 0.6″. Webb also noted, in 1878, that he was able to suspect division in ω Leonis, then at 0.52″, and to divide η Coronae Borealis at 0.55″. It was magic like this that convinced Espin to purchase his first truly ‘serious’ telescope; a 17.25-inch silvered glass reflector by Calver, purchased on Webb’s recommendation in 1885. Espin most likely purchased the mirrors separately and had the castings for his Calver optics made to order by Lepard & Sons of Great Yarmouth as well as by the agricultural firm, Suffolk Iron Foundry, then located near Stowmarket. Espin constructed a modest observatory based on the design of the Reverend Edward Lyon Berthon (1813–1899), another clerical astronomer, which consisted of a small ­circular equatorial room with a conical roof, and which was commonly known as a ‘Romsey,’ after the Parish in which Berthon lived and worked. Espin likely mounted his new instrument on an early equatorial (sometimes called an ‘equestrian’) designed by George With and Edward Berthon (see below). Shortly before his death in 1885, Webb had alerted Espin to the work of John Birmingham on the red stars. In the months before he died, Birmingham dispatched much of his unpublished work to Webb, requesting that he might carry on his observations. Because of his many other duties and failing health, Webb was unfortunately unable to commit to such an undertaking, yet he found a willing and able disciple in the young and enthusiastic Espin.

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A Curious Aside Which is a better tool for red star hunting: a 5-inch refractor or an 8-inch reflector? Method  A Baader 8–24-mm zoom eyepiece was chosen to give an approximate exit pupil of about 2-mm in both the 5-inch refractor and the 8-inch reflector, delivering powers of 64 and 100x, respectively. Both instruments were turned on the Double Cluster (Caldwell 14) in Perseus on a dark, moonless evening and the views compared, side by side, for several minutes. Results  Though the images served up by both telescopes were very fine indeed, the easy winner was the 8-inch Newtonian. The contrast was a shade better in the unobstructed refractor, as one might expect, but the Newtonian, with its 22 percent linear obstruction, wasn’t far behind it. These magnificent open clusters contain quite a few ruby stars of varying glory, but the greater light gathering power of the Newtonian (∼1 visual magnitude) made these stars considerably easier to pick out against a dark hinterland compared with the 5-inch glass. The color of fainter members, in particular, was easier to discern in the Newtonian, a consequence, I suppose, of its greater ability to collect light. Put another way, where there is but a suggestion of color in the refractor, it is clearly visible in the Newtonian. From a practical point of view, it was also much easier to study these ruddy stars in the Newtonian, owing to its more comfortable eyepiece position while viewing an object high in the sky. Comments  More light delivered to the retinal cone cells render color vision more efficacious with the larger aperture. Indeed, no matter how much this author wanted the 5-inch refractor to win, owing to its elegant images, striking good looks, and much greater cost in comparison to the ‘glorified toilet roll’ that is the Dobsonian, it was never to be. Indeed, on all celestial targets examined, under reasonable to good seeing conditions, whether planetary, lunar, double star or deep sky, the Newtonian proved noticeably superior. A comparative MTF graph of a 5-inch refractor and 8-inch reflector will also show this clearly. Many lines of evidence lead to the same conclusion. The 8-inch Newtonian was the superior instrument for hunting down and viewing red stars. This aperture is probably optimal for all kinds of general purpose viewing, including looking at red stars. Thoughtfully designed Newtonians can do wonderful things! With his newly acquired 17.25-inch Calver Newtonian installed, Espin, together with his paid assistant, William Milburn, began a new and ambitious search for red stars all across the northern sky. Over the next 2 years, he found an incredible 3800 red stars, discovered many new nebulae and over 30 novel variable stars. Such work called for considerable industry and his preserved records indicate that during the dark winter evenings, observing vigils were maintained for over 13  h! Using an

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entirely homebuilt spectroscope, he examined over 100,000 stars from Dr. Argelander’s celebrated star charts, with magnitudes as faint as +9.0. These new data were included in a much more extensive edition of The red stars, which also included contributions from Webb, Copeland, Birmingham and Dreyer, and published, once again by the Royal Irish Academy in 1890. The same telescope was used by Espin and Milburn to discover 2575 double stars, many of which were measured micrometrically to establish position angles and angular separations. This body of work was the first all sky search for double stars conducted entirely with a reflecting telescope since the days of Sir John Herschel. Espin’s proven skill as an inventor was also seen in the many new astronomical devices he made with his own hands, including arguably the first zoom eyepiece offering an assortment of magnifications, a new kind of stellar camera, as well as an improved method of lighting the cross hairs of the micrometer. To the general public, such routine work as this often went unreported, but Espin received international fame in November 1910 with the discovery of Nova Lacertae, which burst onto the scene with a peak magnitude of 4.6. Over the next 37 days, as the world’s largest telescopes were turned on it, the nova slowly faded back to 7.6 and today it is exceedingly faint at magnitude 14. Espin was also the first astronomer to point out the Cocoon Nebula (IC 5146) in Cygnus. For his great contributions to astronomical knowledge, Thomas was awarded the Jackson Gwilt Medal of the Royal Astronomical Society in 1914 for his extensive spectroscopic work, as well as his discovery of Nova Lacertae. It was in the same year that Espin installed an even more powerful telescope at Tow Law; a 24 inch Calver reflector, with which he and his assistant continued to look for and measure new double stars. Curiously, Espin decided to concentrate his efforts on wider pairs, perhaps as a result of noting that the typical atmospheric conditions he enjoyed at Tow Law, Co. Durham, were rarely up to measuring very close pairs. This was the last telescope Espin would acquire and he used it faithfully right up until 2 years before his death on December 2, 1934, aged 76. His estate was worth £12, 399.

The Nature and Significance of Red Stars Red stars, which include the spectral classes M, R, N and S, are not only visually striking to the human eye, standing out against the darkness of the night sky more readily than those with different hues, but they are arguably some of the most fascinating to study! First off, red stars not only include celebrated giant stars such as Betelgeuse, but they also incorporate the smallest bona fide stars in the firmament; the cool dwarf stars that comprise maybe 70 to 80 per cent of all stars that exist throughout the Universe. The largest and most luminous of the red giant stars are some 50 billion times brighter than the coolest red stars (none of which can be seen without a telescope), though they all have effective temperatures ranging from about 3900 K (M0) down to 2600 K (M8). Their spectra are littered with a maze of strong absorption lines,

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betraying the presence of simple molecules that absorb light in their tenuous, low gravity atmospheres, including substances such as TiO, CN, ZrO, C3, C2, and CO amongst others. Indeed, these substances collectively absorb so much light (particularly at shorter wavelengths) from their cores that astronomers have found them difficult to classify in a coherent way. This is because it can often prove exceedingly difficult to trace out their black body curves, in a way that their basic properties can be inferred in the same manner hotter stars can. Red giant stars that have evolved off the main sequence exhibit substantial mass loss in the form of powerful stellar winds and thermal pulses which expel layers of their outer atmospheres to the cold, dark of interstellar space. Cool, dwarf stars, on the other hand, have hardly changed since their birth, and are so parsimonious in their energy generation that they can continue to exist stably for a trillion years or more. And while highly evolved red giant stars are not considered likely candidates for life bearing planets, there has been quite a lot of attention paid to the environments around cool, red dwarf stars, as locations that might harbor viable life bearing worlds. Doubtless the interested reader may have heard of recent discoveries made by astronomers in regard to a string of planets orbiting close to M dwarf stars. One example widely cited in the media is TRAPPIST-1, located 39.5 light years in the constellation Aquarius. A media frenzy ensued when the team of astronomers monitoring the system announced a cache of seven worlds orbiting the star, all of which were deduced to have broadly Earth sized masses. The scientists, keen to maximize the impact of their work (thereby securing more funds), stressed the observation that three of these planets lie within the water habitable zone (one of several other ‘habitable zones’ that the scientific community need to talk about, openly and honestly) of TRAPPIST-1 and so could conceivably host some kind of life. But it’s always worth taking a closer look at these planets before jumping to sensationalized conclusions. Three of these TRAPPIST-1 worlds (designated b, c and d) are of particular interest to astronomers, lying just 1.66, 2.28 and 3.14 million kilometers, respectively, from the dwarf red star’s surface. This means that they will be tidally locked to their star and thus will always show the same face to it as they move in their orbits. This creates potentially enormous differences in the temperatures of the day and night sides of the planets, which doesn’t bode well for life. They are also sufficiently massive and close to each other to exert periodic gravitational influences on one another. These induced perturbations likely rule out the possibility of life on these planets, since it would destabilize and frustrate the travails of any emergent life forms on these worlds. Compounding these difficulties is the physical properties of these dwarf stars. Though only 8% the mass of the Sun, recent XMM Newton observations showed its emission of X-rays is comparable to that of the Sun and, owing to their very close proximity to TRAPPIST-1, the resulting X-ray irradiance would likely strip away any primordial atmospheres they might have had. Then, to add insult to injury, many of these stars exhibit strong stellar winds, especially in their younger days, when they were engaged in the nurturing of planetary systems. This would require the

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planets to possess magnetic fields several times stronger than that of Earth in order to stave off the certain extirpation of any putative life forms on their surfaces. In short, many of the popular reports about the habitability of extrasolar planets do so with a large dose of (unbridled) speculation. Further scientific studies of such worlds invariably show that our optimism about whether they harbor life is somewhat misplaced. As in any other avenue of human enquiry; time will ultimately reveal the truth.

Sources Chapman, A.: The Victorian Amateur Astronomer. Gracewing, Leominister, Herefordshire (2017) Cowan, R.: Wind may deflate search for habitable planets: http://www.nature.com/news/ wind-may-deflate-search-for-habitable-planets-1.15335 W.  M.: Obituary: The Rev. T.  H. E.  C. Espin. http://adsabs.harvard.edu//full/seri/ Obs../0058//0000027.000.html. The Trappist-1 Planetary system. https://en.wikipedia.org/ wiki/TRAPPIST-1 Mohr, P.: A Star in the Western Sky: John Birmingham, Astronomer and Poet. http://articles.adsabs. harvard.edu/full/2004AntAs...1...23M Philips, T.E.R.:Obituary Notices: Fellows:– Espin, Thomas Henry Espinell Compton. http:// adsabs.harvard.edu//full/seri/MNRAS/0095//0000319.000.html Wolf, E.T.: Assessing the Habitability of the TRAPPIST-1 System Using a 3D Climate Model: https://arxiv.org/ftp/arxiv/papers/1703/1703.05815.pdf Wheatley, P.J, et al.: Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1. https://arxiv.org/pdf/1605.01564.pdf

Chapter 24

A Historic Clark Telescope Receives a New Lease on Life

In the last decade of the nineteenth century, the wealthy Bostonian oligarch, Percival Lowell, established a grand Observatory atop Mars Hill, Flagstaff, Arizona, some 7250 feet above sea level. Here, in 1894, Lowell had installed a magnificent 24 inch refracting telescope, built by the famous American telescope maker, Alvan Clark & Sons. Fast forward more than a century after Lowell”s death, the telescope has been refurbished and still  wows the public with spectacular views of the night sky (Fig. 24.1).

An Eye on Mars Bought for the princely sum of $20,000 ($500,000  in today’s money), the telescope’s long focal length was ideal for viewing the planets. But there was one world, in particular, that captured Lowell’s imagination: Mars. Back in 1877, the Italian astronomer Giovanni Schiaparelli (1835–1910), had reported seeing networks of linear features on the Martian surface, which he interpreted as ‘canali,’ or ‘channels,’ but he later believed them to be artificial, works of intelligent minds. This was dynamite to Percival Lowell, who dedicated many years of his life to studying the Red Planet through pristine mountain air, far from the lights of towns and cities. Lowell’s many drawings of Mars showed up even more canals than Schiaparelli, many of which were seen to extend from the polar ice caps to the parched equatorial deserts, Lowell published his views in three books: Mars (1895), Mars and Its Canals (1906), and Mars as the Abode of Life (1908). In these writings, Lowell combined his somewhat misguided faith in Darwinian evolution with the latest theories in planetology to popularize the idea of an advanced race of intelligent beings desperately trying to survive on a dying planet. Lowell’s far-fetched ideas inspired others to create a new generation of science fiction literature, most celebrated of which was H. G. Wells’ influential The War of the Worlds.

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Fig. 24.1  The newly refurbished 24-inch Clark refractor used by Percival Lowell to carry out his Martian observations. (Image courtesy of Sarah Conant, Lowell Observatory)

Ultimately, many of Lowell’s ideas turned out to be false. When other highly experienced observers, such as E.E. Barnard and Eugene Antoniadi, who had access to even larger and more powerful refracting telescopes than Lowell’s 24-inch, examined the Martian disk, they could not see any linear features. Indeed, they maintained that when seen through larger telescopes, the so-called canals resolved down to darkly shaded dots that looked completely natural and not artificial as Lowell had contended. World-wide fame and affection soon turned to ridicule, as more and more evidence was amassed against his fanciful theory of advanced Martian beings. Perhaps the most scathing of all came from the British naturalist, Alfred Russell Wallace, who quipped that only a race of madmen would construct canals on this small desert world (Fig. 24.2).

A Revered Instrument Because of its unique provenance, the 24-inch Clark refractor at Lowell Observatory became one of the most celebrated telescopes in the history of astronomy. The late Sir Patrick Moore once claimed that it was his favorite telescope. The instrument is

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Fig. 24.2  Another view of the restored 24-inch Clark at Lowell Observatory. (Image courtesy of Kevin Schindler, Lowell Observatory)

massive, fully 32.1 feet (9.77 m) in length (f/16), with a tube made of riveted steel. Lowell mounted two other instruments alongside the main telescope, also refractors of 12-inch and 6-inch aperture, either of which could have served as the centerpiece of a small college observatory in their own right. The telescope was placed on a massive, state-of-the art equatorial mount. The vaulted dome in which the great telescope was housed, was designed by an ex-cowboy-turned-machinist, Godfrey Sykes, and was erected from hatchet-hewn ponderosa pine timber by a team of ten laborers in as many days!

A New Career in Education After Percival Lowell passed away in 1916, the 24-inch continued to be used for research but in recent years it has been completely dedicated to public outreach, attracting about 85,000 visitors per year. As one might imagine, time had taken its toll on the famous instrument and in 2015 the staff at Lowell Observatory initiated an extensive refurbishment project for the 24-inch Clark. I contacted Kevin

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Schindler, resident historian at Lowell observatory, who kindly answered some questions I had about the project. What was the primary motivation for restoring the Lowell 24-inch Clark refractor? “The main reason was the telescope getting more and more difficult to move in recent years, said Schindler, “The telescope is moved by hand, and historically a person could actually push it with one finger. But by 2013, it was so hard to push that some people simply weren’t strong enough to push it. Plus, the telescope had developed a tendency to ‘clunk’ when moved in a certain position, and this was clearly getting worse. As it turns out (we didn’t know this until the telescope was disassembled), both problems were caused by flattening of the main bearing. A new bearing was built and now those problems are gone. The old clock driven mount has also been replaced by a state-of-the art GOTO system to greatly speed up the pointing of the telescope during public outreach events.” How much money had to be raised to fund the cost of the telescope’s restoration? Did the team receive any grants or bursaries to meet costs? We raised nearly $300,000 for the project, Schindler explained, “Two different sources  – a private individual named Joe Orr (since deceased) and the Toomey Foundation for the Natural Sciences each contributed $100,000. We also raised money via crowd-sourcing efforts and many individual contributions”. Could you provide a brief break down of the individuals/firms involved in refurbishing the instrument and which projects were assigned to whom? The majority of work was done in-house,” Schindler told me, “under the management of Lowell’s Director of Technical Services, Ralph Nye. Other Lowell staff that played significant roles included: Peter Rosenthal, who refurbished most of the telescope controls (including a full powder coating for the tube) and ancillary parts, Jeff Gehring, who machined many new parts for the telescope, Glenn Hill, who refurbished the walls and floor of the dome, and Dave Shuck, who created a new landscape outside the dome. Others were involved, and the people listed above helped each other out, but this is the basic leadership duties of the project.” How do you think these restorations will be received by the public? “The public will be quite excited about the restoration,” explained Schindler, “the Clark is one of the primary reasons visitors come to Lowell. They’ll be thrilled both because the telescope will be working better than ever, making for a more pleasant viewing experience, and also because the telescope is now visually stunning. Also, the Clark Telescope has been in Flagstaff since 1896, and its dome is an icon of the Flagstaff skyline. It is a cherished part of the very fabric of Flagstaff.” Will the instrument continue to be used to train undergraduates and/or as a research instrument in its own right? “The telescope will be used solely for public education, Schindler told me, “The Observatory is open seven days and six nights per week, and the telescope is a critical part of both the day and night-time experience. No plans are on the table to use it for research, and undergraduates will continue to be trained on modern research telescopes.”

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In addition to the mechanical work, the massive, air-spaced doublet objective of the Clark had to be carefully cleaned. Over the last few years, brush fires have laden the air thick with sooty particulates which were deposited on the outer surface of the lens, decreasing its light transmission and increasing light scatter in the images. This has necessitated the removal of the lens cell from the telescope every 2 years or so for cleaning. Many observers have visited Lowell observatory over the years and commented on the fine views the telescope has delivered. For many, the 24-inch Clark represents arguably the finest telescope made by Alvan Clark & Sons. Although the firm did produce larger instruments, such as the 36-inch Lick and 40-inch at Yerkes Observatory, the sheer weight of the glass has caused them to warp under their own weight. The 24-inch, in contrast, has not warped over the years and still provides stunning views of the heavens (Fig. 24.3).

Fig. 24.3  A large crane removes the telescope mount for refurbishment. (Image courtesy of Kevin Schindler, Lowell Observatory)

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Splendid Views I asked Kevin Schindler to tell me about some of the most memorable views he has enjoyed through the Clark over the years. “Regarding memories of excellent seeing conditions, two come to mind,” Schindler explained, “the first must have been in the early 2000s. I had looked through the Clark for years by that time, but this was the first time the conditions were good enough to slip a 14-mm eyepiece into the Clark and, for the first time for me, resolve Jupiter’s moons as disks; I could also clearly distinguish some color, and this experience was almost surreal in its splendor. The other time was during the 2003 Mars opposition, when I could distinguish Phobos and Deimos. That was not visually stunning but a 10 on the coolness scale.” As amateur astronomers, we all hope that the restorations to this iconic telescope will inspire a whole new generation of star gazers. And while there is most certainly no life on Mars as Lowell understood it, the spirit of his legacy lives on as we continue to look skywards for answers to our deepest questions.

Chapter 25

A Short Commentary on Percival Lowell’s “Mars as the Abode of Life”

Biographical Sketch Percival Lawrence Lowell was born in Boston, Massachusetts, on March 13, 1855, the eldest son of Augustus and Katherine Bigelow Lowell. A ‘patrician’ American family, the Lowells were financially successful and politically well-connected. Their wealth could be traced to the efforts of an ancestor, Francis Cabot Lowell, Percival’s great-great uncle, who, after visiting the mechanized textile mills of Lancashire, in northern England, returned to the ‘colonies’ with his own ideas to establish a cotton mill at Waltham, MA. Such a venture was to dramatically change the fortunes of the family, propelling them to the top of the social pecking order (Fig. 25.1). Lowell’s father presided over his many business ventures with an iron fist, becoming widely known as a martinet in all that he set his mind to. Not content to let his children wallow in the prosperities accrued by earlier generations of the family, Augustus expected them to excel at whatever they set their mind to. And in this capacity, they fulfilled that duty. Percival’s younger brother, Abbot Lawrence Lowell (1856–1943) became a distinguished educator and legal scholar, serving as president of Harvard University from 1909 to 1933. His much younger sister, Amy (1874–1925), became a well-known poet and was posthumously awarded the prestigious Pulitzer Prize for poetry in 1926. Percival himself was enrolled in various private schools at home and abroad, eventually attending Harvard, where he excelled at both English literature and mathematics, graduating with honors in 1876. So proficient was Lowell at mathematics, that one of his professors, Benjamin Peirce, invited him to stay at the University to teach the subject, but he declined, later recalling that, “I preferred not to tie myself down …. not because mathematics had not appealed to me as the thing most worthy of thought in the world.” Adventurous and self-confident, the young, Bohemian Lowell took himself off to A Work Dedicated to Dr. Paul G. Abel. © Springer Nature Switzerland AG 2018 N. English, Chronicling the Golden Age of Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-319-97707-2_25

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Fig. 25.1  Adventurer in thought, Percival Lowell (1855–1916). (Image courtesy of Wiki Commons. https://en. wikipedia.org/wiki/ Percival_Lowell#/media/ File:Percival_Lowell.jpg)

Europe on a year-long tour of its capital cities, venturing as far as Syria before returning home in 1877. For the next 6 years, he got stuck into his family’s cotton business, serving as its executive head for a short time. But such work proved far too mundane for Lowell to commit to and so, in 1883, he set off for Japan in search of new interests. This was the first of three trips to the Far East Lowell would embark upon over the next decade. Why he did this is still uncertain, but the young man was known to have cultivated quite an ego, so much so that it made it “almost impossible” for him to settle down in Boston. There, far from home, Lowell would immerse himself in the alien culture of the ‘yellow man’, learning his languages and customs but ultimately conceding that the peoples of the Orient had represented the survival of the unfittest, their ‘evolution’ having been prematurely stunted by their lack of imagination and the suppression of ‘individualism’ within their societies. Lowell’s opinions were strongly shaped by the pervading ideas of his day; social Darwinism. A nation was to be measured ultimately by its gross domestic product, competing with others, both economically and culturally, for a place at the top table. In a Universe infinitely old, with no God looking over his shoulders, it was the only brute reality that made sense to him. This was the world view that shaped his future career and which made him the man he became. Such ideas were set out squarely in his earlier literary works which included Choson: The Land of the Morning Calm, published in 1886, and the Soul of the Far East, which hit the bookshelves in 1888. Lowell’s foray into telescopic astronomy began early, when his mother gifted him a fine 2.5-inch Clark refractor at the tender age of 16. From the opulence of his family mansion at Sevenels, Heath Street, Boston, he would observe the heavens. It was around this time also that his life-long interest in the planets was stoked. In the

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fertile playground of his imagination, Lowell believed that the celestial worlds beyond the Earth were places where, “our wildest fancies may be commonplace facts.” He likened the great observers of his day to Columbus of old, discovering and exploring brave new worlds. What better way to dedicate one’s life than to join in the search to uncover something of the culture of these ‘civilizations in the sky,’ which had evolved completely independently of those on Earth. One man in particular, embodied the spirit of this new age of exploration, the Italian astronomer, Giovanni Schiaparelli (1835–1910), who, during the Great Opposition of 1877, observed a dense network of linear structures through his telescope on the surface of Mars which he called “canali” in Italian, meaning “channels” but which became mistranslated into English as “canals.” His admiration for the Italian visionary comes into sharp focus in Lowell’s earlier work: “Mars and its Canals (1906). “To Schiaparelli”, he wrote, “the republic of science owes a new and vast domain. His genius first detected those strange new markings on the Martian disk which have proved a portal to all that has since been seen…. He made there voyage after voyage, much as Columbus did on Earth, with even less of recognition from home”. With the news of Schiaparelli’s failing eyesight in the mid-1890s, Lowell took it upon himself to continue the work that he had begun. Lowell had acquired considerable experience with larger telescopes. Indeed, a 6-inch Clark achromatic had accompanied him whilst travelling to Japan. But to carry out serious research on the Red Planet, Lowell began to look for larger instruments. His influence at Harvard allowed him to borrow a fine 12-inch Clark and he even convinced the trustees at Harvard College to enlist the services of the staff astronomers to scout out locations in the American southwest where the seeing conditions were particularly good for planetary observation. Eventually, Lowell decided to build an observatory at Flagstaff, Arizona, where he would carry out the majority of his observations of the planet Mars. At a cost of $20,000 (over $500,000 in today’s currency), the main instrument chosen by Lowell was massive, fully 2 feet across (24 inches clear aperture) with a focal length of 32 feet (f/16), the optics housed in a tube fashioned from riveted steel (see Figs. 144 and 145). Lowell mounted two other instruments alongside the main telescope, also refractors of 12-inch and 6-inch aperture. The telescope was placed on a massive clock-driven equatorial mount, which tracked the heavens with precision for several hours on end. The magnificent 24-inch Clark was the primary instrument used by Lowell to conduct his Martian studies and his observations formed the basis of his famous books on the subject of extraterrestrial life. As we have seen (at a cost of $300,000 provided by public donations and private benefactors), the historic telescope has (as of 2015) received a new lease of life to inspire future generations of star gazers. In 1908, at the age of 53, Lowell married Constance Savage Keith (1863–1954), 8 years his younger. Well connected, Constance made her name and her money in the real estate business. Indeed, the couple first became acquainted when he bought a property from her. They honeymooned in London, taking a hot air balloon ride over Hyde Park in order that he could photograph the landscape. Quite possibly,

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Lowell was thinking of the Martian canals he had seen through his telescope and wanted something to compare them with. Constance outlived her husband by nearly four decades, spending most of that time as a recluse before passing away at the ripe old age of 91. Author’s Notes on the Preface  The trustees of the observatory encouraged Professor Lowell to popularize his ideas about life on Mars through a series of public lectures, setting out, in a step-by-step manner, the scheme of events, as he understood them, that shaped the evolution of the Red Planet. The lectures he conducted were an over-night success, mesmerizing his audiences with a sincere and compelling vision of how life arose on Mars and evolved through Darwinian means to create a race of intelligent beings fighting desperately to survive on a dying, desert planet. People from all around the world flocked to hear the urbane astronomer deliver his sensational allegory. The book was a lucrative spin-off of these lectures and became an international bestseller. Then, as now, there was no shortage of people who were all too eager to believe it but was it grounded in any reality? Alas, no!

Chapter I: The Genesis of a World Covering Pages 1–35 In this opening chapter, Lowell recounts the cosmogeny of the Solar System, in which he imagined the Sun and its retinue of worlds being formed from gas and dust that had slowly coalesced under the auspices of gravity, heating up as they did. To Lowell, it was the property of mass itself that determined the evolutionary fate of the Sun and the planetary bodies, an idea that still holds currency with us today. Lowell believed that the stuff of the heavens and of the Earth were one and the same. As evidence, he discusses the properties of meteorites – stony or metallic in character – in which some 26 of the same chemical elements were found to constitute them and not one that did not occur on Earth. To Lowell, this provided powerful evidence that whatever occurred on Earth must inevitably occur on other worlds, including Mars. Lowell then presents six stages of planetary formation from “sun to cinder.” The size and mass of the body ultimately dictating whether it would remain in a primordial state or could evolve through various stages. These stages (p. 12) he identified as: I. The Sun stage: Hot enough to emit light. II. The Molten Stage, hot and lifeless. III. The Solidifying Stage, where solid surfaces formed. Ocean basins determined. Age of metamorphic rocks. IV. The Terraqueous Stage: Age of Sedimentary rocks. V. The Terrestrial Stage: Oceans have disappeared. VI. The Dead Stage. Air Has Departed.

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In this scheme, Professor Lowell considered the outermost planets; Jupiter, Saturn, Uranus and Neptune in the 2nd ‘planetological’ stage. Earth was at Stage IV, Mars, V and the Moon at the sixth (VI). Note that Lowell took it ipso facto that the planets were not the same age. Jupiter, for example, was younger than the Earth, Mars older. As one proceeds to read more of this chapter, one gets the distinct impression that Lowell was not so proficient with