JOHN MICHELL'S THEORY OF MATTER AND JOSEPH PRIESTLEY'S USE OF IT John Schondelmayer Parry muster Doe4e..T of Philosophy Department of History of Science and Technology, Imperial College of Science and Technology, University of London 2 ABSTRACT John Michell (1724-1793) developed a theory of penetrable matter in which a bi -polar (attractive and repulsive) power consti- tuted substance, and made itself sensible through the properties of matter. His sensationalist epistemology was similar to Locke's, though he denied the essential passivity and impenetrability of matter which both Locke and Newton had espoused in favour of a monist synthesis of matter and power. Michell supposed that immediate contact and the mutual penetration of matter were not absolutely prevented but only inhibited by repulsive powers at the surfaces of bodies, and he explained light's emission, momentum and resulting ability to penetrate transparent substances by the interaction of the powers of light particles with the surface powers of luminous bodies and receiving bodies. Joseph Priestley (1733-1804) adopted many of Michell's ideas on matter and light, and described them in his History of Optics, (1 772) . Nckli fritmdsh,i0, frurn, 17In8, Wed. Wte die v's i r*rest. '1■-■ ihcb o f mg-Tier, et.d helpcd k.11-, See *its pzie4ic, t He accepted Michell's ideas on penetrability, immediate contact, and the basic role of powers, a5 well Qs -4e tp;st-th)Divlb 1.z1A4.0k. tive5-e ides; and ; (A-Oz I 464.5 prtroiclect 114A t41.41, 4 he hears whereby kiz GoLa ci areept "to red*Fh-e aheitxpii.ectik tot,sicit.1 ancArnerci( AS;(4) ci-crls.13,nesifle_ extended Michell's theory and epistemology of matter, applying it in psychology and metaphysics as well as natural philo- sophy to arrive at an implicit monist system of powers ascending from the physical powers of attraction and repulsion through chem- ical and biological powers to the powers of mind, with all the powers 3 created and sustained by the powers of God; and he thus integrated the perceiving human mind and perceived substance in a dynamic metaphysical system which owed much to the ideas of Michell. 4 TABLE OF CONTENTS Page number Preface 5 Introduction 7 Chapter One: Michell, Savile and Priestley 10 Chapter Two: Michell's Ideas on Magnetism 28 and his Theory of 'Molecular Magnets' Chapter Three: Michell's Ideas on Light and 55 on the Powers and Penetrability of Matter Chapter Four: Priestley's Adoption and Adaptation 87 of Michell's Theory of Matter Chapter Five: Priestley's Application of 116 Michell's Theory of Matter Chapter Six: Rationalism and the Powers and 157 Properties of Substance in Michell and Priestley's Theory of Matter Conclusion 176 Notes and References 180 Bibliography 21 3 5 PREFACE I wish to thank Dr. Marie Boas Hall, my thesis supervisor, for her patience and her invaluable assistance in the preparation of this thesis. The following kindly gave me permission to look at relevant manuscript and printed material: His Grace, the Duke of Devonshire (the Michell-Cavendish correspondence at Chatsworth); the Rare Books Department, University of California at Berkeley (microfilm copies of Roger Boscovich's letters from England in 1760); the Nottingham- shire County Record Office (Savile of Rufford and Foljambe Manu- scripts, and the Bishop's Transcripts of Eakring Parish Registers); the Royal Astronomical Society (Herschel Papers); the Institution of Civil Engineers (Smeaton's Machine letters); the British Museum; the American Philosophical Society (copy of a letter from John Michell to Sir Charles Blagden; the Berkshire County Record Office (several Michell-Savile letters); the Public Record Office; the Guildhall Library; Cambridge University Library; the Lyon Playfair Library (Imperial College); Senate House Library (University of London); the Science Museum Library; the British Museum (Natural History); andDr. Williams' Library. I would like to thank the owners, custodians and staff of these collections for their kind- ness and assistance during my research. I would like to thank the following at the University of Toronto for their generous assistance: Gordon Elliott for his suggestions of sources concerning the Michell-Savile connection; Professor James MacIachlan; Professor Kenneth 0. May; and Professor Trevor Levere, who first pointed out to me the non=Bos- covichean character of Priestley's theory of matter, and thus 6 initiated my interest in the origins of Priestley's theory. Professor George Grinnell of McMaster University was the first to teach me history of science, and his course and his excellence as a teacher inspired me, among others, to study the subject at the postgraduate level. Larry Stewart, who studied with me under Prof- essor Grinnell, and at the University of Toronto, provided me with many helpful suggestions throughout my research on this thesis. I wish to thank Dr. R. Finaldi for his help with translating the Boscovich letters; Mrs. Barbara Nuttall and Mrs. Joan Vincent for their assistance concerning the Michell family; Dr. R. A. Har- vey for information concerning Michell and Cavendish; and Mrs. Jennifer Hardy-Smith for typing the titles of this thesis. My thanks to the members of the Department of the History of Science and Technology at Imperial College for their many kindnesses, questions and suggestions. I would like to thank particularly Alison Yeomans and Riz Shakir, Ali for typing this thesis from an often illegible and constantly changing text, and both her and Riz for their friendship, assistance and encouragement. 7 INTRODUCTION In a letter which he wrote to his friend John Michell in 1785, the civil engineer John Smeaton expressed the wish that Michell might "unravel" some "enigmatical" remarks which he had 1 recently made on the physical structure of the eye. He seems to have taken for granted the "abstruse" nature of his friend's pronouncements, and assumed that there was much substance hidden beneath apparently brief and cryptic remarks. To the modern historian of science, as to John Smeaton, the oroblem of "unravelling" John Michell is a difficult task, and 8 one undertaken with the assumption that there is something to be found which can justify the effort. Lib Whyte's remark in Roger Joseph Boscovich, (London, 1961)2 that Michell was perhaps one of the great matter-theorists of the eighteenth century suggested to me that Michell might well repay the effort involved in study- ing his life and work. Two historians of science in the last decade have published articles on Michell's scientific career which have expanded considerably our knowledge of the life of this "enigmati- cal" man,3 and much remains to be done. Michell's "abstruseness" and his concomitant reluctance to publish concerning his scientific research are the principal reasons for the relative neglect he has received, despite recognition from contemporaries and later historians of science of such accomp- lishments as the discovery of the inverse square law of magnetism, the invention of the torsion balance, the founding of the science of seismology with his method for determining the epicenter of earthquakes, his determination of the strata of England, and his development of the theory of the penetrability of matter. As increasing interest in Michell leads to the discovery of more material and to a more thorough awareness of the breadth and depth of his scientific and technological achievements, the sources of his ideas become somewhat clearer, as do the means whereby he utilized his practical experience with the properties of matter and his theoretical knowledge of mathematics, physics and philosophy to arrive at what amounts to virtually a revolution in theory of matter. The first half of this thesis is concerned with -what Michell thought about the nature of matter, and how he came to that view through a combination of experimentation, observation, reasoning, and the adaption and transfdrmation of the physical, epistemological 9 and and metaphysical ideas of Locke jewton. The principal first-hand source we have for Michell's "doctrine of attractions and repulsions" and his dynamic theory of matter is Joseph Priestley's History and Present State of Discoveries relating to Vision, Light, and Colours, (London, 1772). This work was in part the product of collaboration with Michell between 1768 and 1772, and Priestley acknowledged his debt to Michell in the History. Priestley also acknowledged the importance of the theory of point-atoms or "puncta" advanced by Roger Joseph Boscovich; but I hope to show that Michell was the chief formative influence on Priestley's developing theory of matter. Priestley's own theory, and even his reading of Boscovich's theory were principally shaped by the ideas which Michell had imparted to him. Priestley's discuss- ion of Boscovich in fact points implioitly to differences between Michell's and Boscovich's theory over basic physical, epistemolo- gical and metaphysical questions, and although Priestley assumed the theories of the two men to be virtually identical, his misinter- pretation ofBoscovich, influenced, I hope to show, by his earlier familiarity with Michell's ideas, helps to olarify those very differences. Priestley adopted and applied Michell's dynamic and monistio theory of substance to psychology, metaphysics and theology in the mid-1770's, and its influence can be seen in the importance ascribed to properties and powers in some of his other work of the period. The second half of this thesis accordingly deals with Priestley's adoption, presentation and application of Michell's theory of matter. 10 CHAPTER ONE MICHELL, SAVILE AND PRIESTLEY -(1) There are three principal accounts of the life and scientific career of John Miohell: Agnes Mary Clerke's article "John Michell" irr the Dictionary of National. Biography (1888), Arohibald Geikie's Memoir of John Michell (1918), and Clyde L.