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UNIVERSITY OF OKLAHOMA GRADUATE COLLEGE THEORIES OF COMETS TO THE AGE OF LAPLACE A Dissertation SUBMITTED TO THE GRADUATE FACULTY in partial fulfillment of the requirements for the degree of Doctor of Philosophy By TOFIGH HEIDARZADEH Norman, Oklahoma 2004 UMI Number: 3149289 UMI Microform 3149289 Copyright 2005 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 kCopyright by TOFIGH HEIDARZADEH 2004 All Rights Reserved To Farzaneh and Nikoo for their endless love and support iv ACKNOWLEDGMENT This dissertation would not have been possible without the encouragement and generous help of my supervisor, Prof. Peter Barker, who not only taught me how to conduct research but also educated me in how to be a patient and understanding educator. His gracious contribution made the completion of this project achievable and has left its indelible mark on the entire work, and my debt to him is lasting. I would also like to thank the members of my dissertation committee: Prof. Steven J. Livesey, Prof. Kenneth L. Taylor, Prof. Marilyn B. Ogilvie, and Prof. Kieran Mullen for their willingness to read this work and for their valuable comments. Several other scholars from different organizations were also contributed in this project by providing documents, pictures and rare books. I would like to express appreciation to Prof. Ekmeleddin øhsano÷lu (IRCICA, Istanbul), Dr. Donald K. Yeomans (Jet Propulsion Laboratory, Pasadena), Dr. Kerry Magruder (History of Science Collections, the University of Oklahoma, Norman), Dr. James Alan Ruffner, Dr. Niels- Ole Prægel (senior scientist, University Library, Copenhagen), Lone Gross (the Astronomical Observatory at the University of Copenhagen), Dr. William Griffith (the Millington/Bernard Collection at the University of Mississipi), Prof. Nasser Nafari (Knox College, Galesburg, Illinois), and the librarians of the Huntington Library and Art Collections (Pasadena, California) for their kind help. My father passed away when I was at the beginning of this project. Using a Persian maxim in his last letter, he reminded me that “success and rest cannot exist together.” His incessant support, together with my mother’s continuous encouragement were always invaluable sources of aspiration for me. To appreciate their attention and care is an unending task for me. Finally, in acknowledging those who means so much to me I come to my wife, Farzaneh and my daughter, Nikoo. This work is dedicated to them but, I am sure, that hardly settles the debt. Through several years that I have been physically with them but mentally with this project, their love has been unconditional. v TABLE OF CONTENTS Introduction………………………………………………………………………….1 Chapter one: Aristotle’s Theory of Comets ……………………………………….. 3 The Aristotelian Structure of the Sub-lunar Region..……………………...... 8 Shooting Stars……………………………………………………………. ...14 Comets: Formation and Kinds…………….……………………………….. 15 The Milky Way…………………………………………………………….. 25 Aristotle’s Theory of Comets: A General Evaluation……..………………..26 Chapter Two: After Aristotle Non-Aristotelian Theory of Comets Seneca……………………………………………………………………….32 Continuation of Aristotle’s Meteorology in the Early Medieval and Islamic Era.………………………………………………………… 35 Comets in the Islamic World .……………...……………………………….43 At the Threshold of the Quantitative Study of Comets: From Peter of Limoges to Regiomontanus………………………….51 Antisolarity of the Tail: A New Chapter in Cometology…...…………… 57 Parallax………………………………………………………….………….60 Tycho Brahe and the Comet of 1577..…………….………………………..63 Brahe’s Optical Theory of Comets…………………………………………70 Tycho’s Contemporaries……………………………………………………72 Conclusion…………………………………………………………………..77 Chapter Three: From Brahe to Newton...………………………………………... 82 Comets of 1618: The Great Debate…………………………………………87 Galileo’s Comet……………………………………………………..………94 Kepler’s Theory of Comets..………………………………………………100 Comets in Descartes’ Cosmos..……………………………………………105 A Comet’s Trajectory Among the Vortices..….……….…………..115 Descartes’ Theory of Cometary Tails..…………………………….118 Conclusion…………………………………………………………………128 Chapter Four: Comets in Newtonian Physics Newton’s Introduction to Cometary Astronomy......………………………134 Comets in the Principia…………………………………………... 140 Comets in the Opticks and Later Works…………………………..155 Physical Properties of Comets According to Newton: A General Assessment..………………………………………………………160 The Cosmological Roles of Newton’s Comet versus its Physical Constitution.……………………………………………………….177 Conclusion…………………………………………………………………184 vi Chapter Five: After Newton The Post-Newtonian Newtonian Theories of Comets…..……………….. .190 William Whiston and Edmund Halley.......……………………….196 David Gregory..…………………………………………………..205 Henry Pemberton…………………………………………………212 François Marie Arouet (Voltaire)………………………………...214 Roger Long……………………………………………………….218 Colin Maclaurin…………………………………………………..220 Conclusion….……………………………………………………………..223 Chapter Six: Non-Newtonian Theories of Comets..……………………………..229 Mairan’s Theory of Cometary Tails………………………………233 John Rowning....…………………………………………………..237 Euler’s Theory of Tail Formation…………………………………241 Immanuel Kant: Cosmogony of Comets…….…………………………….249 The Age of Electricity………….………………………………………….256 Hugh Hamilton……………………………………………………265 Conclusion..….……………………………………………………………279 Chapter Seven: Comets in the Laplacian Cosmos……………………………….284 Herschel’s Evolving Universe.……………………………………………286 Pierre-Simon Marquis de Laplace………………………………………...293 The Origin of Comets: A Probablistic Approach…………………294 The Mass of Comets………………………………………………298 The Structure of Comets…………………………………………..302 Comets and the Nebular Hypothesis……………………………....311 Conclusion…………………………………………………………………314 Summary and Concluding Remarks...…………………………………………318 Appendix…………………………………………………………………………326 Bibliography...…………………………………………………………………...305 vii INTRODUCTION Although the development of ideas about cometary motion has been investigated in several projects, a comprehensive and detailed survey of physical theories of comets has not been conducted. The available works either illustrate relatively short periods in the history of physical cometology or portray a landscape view without adequate details. The present study is an attempt to depict the details of the major physical theories of comets from Aristotle to the age of Laplace. The basic question from which this project originated was simple: how did natural philosophers and astronomers define the nature and place of a new category of celestial objects- the- comets after Brahe's estimation of cometary distances? However, a study starting merely from Brahe without covering classical and medieval thought about comets would be incomplete. Thus, based on the fundamental physical characteristics attributed to comets, the history of cometology may be divided into three periods: from Aristotle to Brahe, in which comets were assumed to be meteorological phenomena; from Brahe to Newton, when comets were admitted as celestial bodies but with unknown trajectories; and from Newton to Laplace, in which they were treated as members of the solar system having more or less the same properties of the planets. By estimating the mass of comets in the 1800s, Laplace diverted cometology into a different direction wherein they were considered among the smallest bodies in the solar system and deprived of the most important properties that had been used to explain their physical constitution during the previous two millenia. Ideas about the astrological aspects of comets are not considered in this study. Also, topics concerning the motion of comets are explained to the extent that is helpful in 1 illustrating their physical properties. The main objective is to demonstrate the foundations of physical theories of comets, and the interaction between observational and mathematical astronomy, and the physical sciences in defining the properties of comets. The number of publications containing ideas about the physical properties of comets shows a radical increase in the third period of our account of cometology. From numerous general astronomy texts or treatises devoted to comets in this period, those were discussed here that either proposed a different theory of comets or criticized the physical aspects of contemporary theories. The survey includes only works published in England and France, and a few in German-speaking countries. Although Laplace's achievement in estimation of cometary masses became the basis of modern cometology, our current ideas about the actual size, mass and composition of comets, and the processes by which the coma and tail are formed have been developed only since the mid twentieth century. Post-Laplacian developments in the study of comets are highlighted in an appendix, which briefly reviews the major achievements in the observational and theoretical study of comets in the nineteenth and the twentieth centuries. Although the present study is mainly focused on the physical theories of comets, its results will be relevant to studies in the history of geology, planetary science, and astrology. On the other hand, those results may initiate new studies about educational practices for physics and astronomy in post-Newtonian Europe, the ways that different parts of Newton' s physical, astronomical and cosmological ideas evolved after him, and the influence of cometary studies on