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MEMOIR 
 
 OF 
 
 JOHN MICHELL 
 
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CAMBRIDGE UNIVERSITY PRESS 
 
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MEMOIR 
 
 OF 
 
 JOHN MICHELL 
 
 M.A., B.D., F.R.S. 
 
 Fellow of Queens' College, Cambridge, 1749 
 
 Wood war Jian Professor of Geology 
 
 in the University 1762 
 
 BY 
 
 SIR ARCHIBALD gEIKIE 
 
 O.M, K.C.B, D.CJ.., D.Sc^ F.R.S. 
 
 CAMBRIDGE 
 AT THE UNIVERSITY PRESS 
 

 
 
JOHN MICHELL 
 
 AMONG the men of science in England 
 during the latter half of the eighteenth 
 century there was one specially remark- 
 able for the wide range of his genius and 
 the originality of his methods of research. 
 As Rector of a quiet country parish in 
 Yorkshire, he lived remote from the centre 
 of the intellectual life of his day, but in 
 that retreat he had time and opportunity 
 for reflection and experiment. Moreover, 
 as he was able to visit London each year, 
 he could keep in touch, not only by cor- 
 respondence but by personal contact, with 
 the leaders of enquiry. Though much 
 esteemed and respected by his contem- 
 poraries, he has perhaps hardly received 
 from subsequent generations the recog- 
 nition lo which the merit of his work 
 justly entitles him. It is true that some 
 
 G. I 
 
historians who have recorded the progress 
 of the sciences to which he devoted his 
 attention have alluded more or less fully 
 to his published papers. But it is not 
 until a review is made of his contributions 
 to each of the sciences of geology, physics 
 and astronomy that an adequate concep- 
 tion can be formed of the place that is due 
 to him in the history of English science. 
 Recent researches among the archives 
 of the Royal Society and of its dining 
 Club brought the name of this modest 
 investigator so frequently before me as to 
 rouse my interest in his career. I was 
 induced to search for any personal details 
 regarding him that might still be recover- 
 able, and to peruse such of his writings as 
 I had not previously read. As the result 
 of this enquiry I have thought it to be 
 my duty to bring his life and his solid 
 achievements in science more promi- 
 nently to notice. Hence the origin of 
 the present Memoir. 
 
JOHN MICHELL, the friend of Henry 
 Cavendish and Joseph Priestley, has left 
 no record of his life beyond his published 
 writings. A few of his letters have sur- 
 vived. Several of them addressed to Sir 
 William Herschel have been found among 
 that philosopher's manuscripts, and are 
 quoted in the collected edition of his 
 Papers. A long and hitherto unpublished 
 letter from Michell to Cavendish has 
 been preserved among the papers of that 
 great man, and is inserted in the present 
 Memoir 1 . 
 
 It is not quite certain where and when 
 Michell was born. Probably his native 
 place was Nottingham, and the year of 
 his birth 1 724. Of his parentage nothing 
 appears to be known. The earliest 
 accounts of him which have been re- 
 covered are preserved in the registers of 
 
 Queens' College, Cambridge, where a full 
 
 
 
 1 This letter was known to Dr George Wilson, 
 Cavendish's biographer, and is referred to by him 
 in the Life (portea^ p. 47). 
 
 3 
 
record has been kept of his College life, 
 from the time of his admission as Pen- 
 sioner on 1 7th June 1742, until, after 
 taking his degrees and filling many offices 
 during a residence of twenty-one years, 
 he quitted Cambridge for a rectory in the 
 country 1 . He is entered in these records 
 as from Nottingham. 
 
 The year after his reception into 
 Queens' he was elected Bible-Clerk and 
 held this office for two years. Again for 
 three years, from 1 747 to 1 749 he filled the 
 same post 2 . Heclid not take his Bachelor's 
 degree until 1748. His name appears as 
 fourth wrangler in the list for 1748-9, 
 which was the second competition after 
 the institution of the wranglership. On 
 3Oth March 1749 he was chosen Fellow 
 
 1 The present President of Queens' College, 
 the Rev. T. C. Fitzpatrick, has been so good as to 
 collect for me all the details of College life that are 
 here given. 
 
 2 The duty of this officer appears to have been 
 to read the Bible in hall, for which a remuneration 
 of one shilling a week was allowed, afterwards slightly 
 increased. 
 
of his College. Thereafter for some 
 fifteen years he continued to fill various 
 lectureships and other offices at Queens'. 
 He was Tutor of the College from 
 1751 to 1 763 ; Praelector in Arithmetic in 
 1751 ; Censor in Theology in 17524; 
 Praelector in Geometry in 1753 ; Prae- 
 lector in Greek in 1755 and 1759; Senior 
 Bursar in 1 7568 ; Praelector in Hebrew 
 in 1759 and 1762 ; Censor in Philosophy 
 and Examiner in 1760. He took his 
 degree of Master of Arts in 1752 and 
 Bachelor of Divinity in 1761. He was 
 nominated Rector of St Botolph's, Cam- 
 bridge, on 28th March 1760, and held 
 this living until June 1763, when he left 
 Cambridge on being collated to a rectory 
 in the country. 
 
 The registers of Queens' College furnish 
 information as to the modest payments 
 made in the eighteenth century to the 
 officials by whom the work of the College 
 was performed. In Michell's case we 
 learn that the largest sum paid to him as 
 
 5 
 
Bible-Clerk was 5. 3-r. lod. for the year 
 1748. Again in 1753 his stipend as Fellow 
 amounted to 9, that of his theological 
 Censorship to 8, and that of his ex- 
 aminership to 2. 
 
 Besides these College duties he held 
 from time to time some University 
 appointments. In July 1754 he was 
 elected to the office of Moderator for the 
 following year. In 1 75 5 he was appointed 
 Taxator 1 and on 24th June 1762 Scrutator 
 for the following year. But the most im- 
 portant office conferred upon him was the 
 Woodwardian Professorship of Geology, 
 to which, near the end of the year 1762, 
 he was appointed by Colonel King, the 
 last surviving executor of John Woodward 
 
 1 The Master of St John's informs me that "the 
 Taxators were appointed by the Colleges according 
 to the cycle for Proctors. They regulated the markets, 
 examined the assize of bread, the lawfulness of 
 weights and measures, and called all abuses and 
 defects into the court of the Commissary. The 
 Scrutators seem to have been assistants to the Proctors. 
 The Proctors read the Graces and took the votes in 
 the Regent House ; the Scrutators did the like in 
 the Non-Regent House." 
 
 6 
 
who by his will dated in 1727 founded 
 the Chair. Michell did not hold the office 
 for quite two years, having to vacate it 
 on his marriage in 1 764. There appears 
 to be no evidence that during his short 
 . tenure of the office he ever gave geological 
 lectures 1 . But the intimate acquaintance 
 with geological phenomena shown in his 
 essay on Earthquakes, communicated to 
 the Royal Society in the spring of 1760, 
 proves that he was well qualified to lecture 
 on a subject which he had pursued with 
 zeal in the field. It is difficult to believe 
 that he did not Impart to his under- 
 graduate friends some of the knowledge 
 which he had gained in many traverses 
 across the southern counties, if indeed he 
 did not take them with him in some of 
 his rambles. 
 
 A brief description of MichelFs per- 
 sonal appearance in his College days, 
 penned by a contemporary diarist and 
 preserved among the manuscripts of the 
 
 1 Life of Adam Stdgwick^ vol. I, p. 192. 
 
 7 
 
British Museum, may be quoted here. 
 "John Michell, BD is a little short Man, 
 of a black Complexion, and fat ; but 
 having no Acquaintance with him, can 
 say little of him. I think he had the Care 
 of St Botolph's Church, while he con- 
 tinued Fellow of Queens' College, where 
 he was esteemed a very ingenious Man, 
 and an excellent Philosopher. He has 
 published some Things in that way, on 
 the Magnet and Electricity V 
 
 Although his time was evidently much 
 engaged in the various official duties that 
 devolved upon him in Cambridge, there is 
 proof that he had already launched upon 
 his career of physical research and experi- 
 mentation within the walls of his College. 
 In 1750, the year after he obtained his 
 Fellowship and when he was some six- 
 and-twenty years of age, he published at 
 Cambridge a little volume on Artificial 
 Magnets to which further reference will 
 
 1 Cole MSS. XXXIH, 156 (Add. MSS. Mus. 
 Brit., 5834). 
 
 8 
 
be made on a later page. As he was fond 
 of constructing his own apparatus, his 
 rooms at Queens' with all his implements 
 and machinery would sometimes wear the 
 look of a workshop, and were no doubt 
 the theme of much amused wonderment 
 among both Fellows and undergraduates. 
 But these mechanical operations and 
 experiments indoors were only a part of 
 the scientific occupations with which he 
 employed his leisure. As above stated, 
 there can be no doubt that he was in the 
 habit of making what would now be 
 called geological excursions, in which he 
 interested himself in noting the distri- 
 bution and sequence of the rock-forma- 
 tions in the southern counties of England. 
 It was only by such practical field-work 
 that he could gain the remarkably accu- 
 rate conception of the structure of the 
 stratified portion of the earth's crust em- 
 bodied in his Earthquake paper of 1760. 
 This epoch-making essay was read to the 
 Royal Society in sections at five successive 
 
 9 
 
evening meetings. The active College 
 Preceptor and Bursar was now introduced 
 into the centre of the scientific life of 
 the time, where he was warmly wel- 
 comed. Immediately after the reading 
 of the first portion of his paper some of 
 the Fellows of the Society drew up and 
 signed a certificate in favour of his elec- 
 tion into the Society. Within a fort- 
 night, and before the reading of his paper 
 was ended, the certificate was in the 
 hands of the Council. It ran as follows : 
 
 The Rev. Mr John Michell M.A. Fellow 
 of Queens' College, Cambridge, who has re- 
 commended himself to the Publick by his 
 Experiments in Magnetism, and has lately 
 communicated to this Society a Dissertation 
 upon Earthquakes, being very desirous of the 
 honour of becoming a member of the Royal 
 Society, We, whose names are underwritten, 
 recommend him as a gentleman extremely 
 well qualify 'd for that honour. 
 
 LONDON, March 6, 1760 
 
 The first names on the list of signa- 
 tures are those of the Secretary of the 
 10 
 
Society, Dr Thomas Birch, and of Mi- 
 chell's contemporary at Queens' College, 
 the active and broad-minded Sir George 
 Savile, Bart., who, after serving in his 
 youth against the Jacobite rebels in 1745, 
 spent a busy and useful life in Parliament 
 as member for Yorkshire. Next comes 
 the name of Dr Gowin Knight, Copley 
 Medallist, and first Principal Librarian 
 of the British Museum, whose researches 
 in magnetism would especially draw him 
 towards Michell. The other signatures 
 include those of Dr Matthew Maty, 
 afterwards Secretary of the Royal Society 
 and Principal Librarian of the British 
 Museum ; Daniel Wray, the antiquary ; 
 and John Hadley, another of the Fellows 
 of Queens' College, who a few years 
 before had been appointed Professor of 
 Chemistry at Cambridge, and with whom 
 Michell would doubtless have much dis- 
 cussion of scientific matters. Michell 
 was duly elected a Fellow of the Royal 
 Society on 1 2th June 1 760. It is worthy 
 
 ii 
 
of notice that the immediately preceding 
 election was that of Henry Cavendish, 
 and that the two names stand together 
 in chronological sequence in the Record 
 of the Society. 
 
 In the spring of the year 1763 Michell 
 gave up his residence at Cambridge and 
 became Rector of Compton in the valley 
 of the Itchin, which winds from Win- 
 chester to the sea. It was not improbably 
 with a view to his marriage that this 
 change of abode was made. The follow- 
 ing announcement appeared in the Cam- 
 bridge Chronicle of 8th September 1764. 
 " A few days ago the Rev. Mr Michell, 
 Rector of Compton, near Winchester, 
 late Fellow of Queens' College, Cam- 
 bridge, and Woodwardian Professor of 
 Fossils in this University, was married 
 to Miss Williamson, a young lady of 
 considerable fortune, near Newark in 
 Nottinghamshire." He did not long 
 retain his living at Compton, for on 
 23rd January 1765, he was collated 
 12 
 
Rector of Havant, Hants. The prospect 
 of a happy married life at this home was 
 rudely dissipated in the autumn of that 
 same year, when his young wife died at 
 Newark 1 . Two years later, on 3rd Oc- 
 tober 1 767, he was instituted Rector of 
 Thornhill, near Dewsbury in Yorkshire, 
 and remained in this office as long as he 
 lived. He subsequently married again 2 . 
 He appears to have had only one child, 
 a daughter, probably by his first wife. 
 This daughter married and is said to have 
 died at an advanced age somewhere about 
 the year 1840. 
 
 In the summer of 1871 there appeared 
 in the journal called the English Mechanic* 
 a communication which gave some pre- 
 viously unpublished information about 
 John MichelL As the writer of the letter 
 stated that he was the great-grandson of 
 
 1 Cambridge Chronicle, 1 2th October 1765. 
 
 * In the church at Thornhill, the burial register 
 records that Ann Michell, relict of the late Rev. 
 J. Michell, Rector, died 6th November 1818. 
 
 1 Vol. xiu, p. 310 (i6th June 1871). 
 
 '3 
 
the philosopher, and that he derived 
 his information from his grandmother, 
 Michell's daughter, considerable import- 
 ance has naturally been attached to his 
 contribution, and its statements have been 
 quoted, though sometimes with hesita- 
 tion, in various biographical notices of 
 his eminent ancestor. It ran as follows : 
 
 After William Herschel's appointment as 
 organist of Halifax, he became acquainted 
 with the Rector of Thornhill, (a village about 
 nine miles from Halifax and six from Wake- 
 field) whose name was John Michell a man 
 of fortune, whose whole life was devoted to 
 science, and whose writings are to be found 
 in considerable numbers in the journals of the 
 Royal Society, during the latter half of the 
 last century, one of the most prominent papers 
 being that on the great Lisbon Earthquake 
 of 1 755. John Michell may perhaps be better 
 known rs the builder of the mathematical 
 bridge across the Cam at Queens' College, 
 Cambridge 1 . He was no mean violinist in 
 
 1 This family tradition is probably an exaggera- 
 tion of any connection which Michell may have 
 had with, the bridge. He obtained his Fellowship 
 at Queens' on 3Oth March 1749. In October of 
 that year it is recorded in the Magnum Journale of 
 
his day, and his soirees where not only the 
 first musical talent, but also the first scientific 
 men of the day, such as Cavendish, Black 
 and Priestley used to meet occasionally were 
 well known in the West Riding of Yorkshire, 
 and to which Wm Herschel used to come to 
 perform on the violin. At the period of 
 these visits Michell was and had long been 
 engaged in making what was at that time a 
 large telescope a ten-foot reflector. The 
 perfect combination for a perfect reflector, 
 and the grinding the same, had long occupied 
 MichelFs attention, in which he at last suc- 
 ceeded, and I believe I am correct in saying 
 that Herschel there became a willing and able 
 pupil, and obtained the germs of his great 
 astronomical renown. At the death of John 
 Michell, all his scientific apparatus were sent 
 to Queens' College, Cambridge, save and ex- 
 cept his large reflecting telescope, which by 
 purchase or gift came into the possession of 
 Wm Herschel. I have been told by the only 
 
 the College that Mr Etheridge was paid 21 for 
 the design and model of the bridge. The construc- 
 tion was not completed until September of the fol- 
 lowing year when the cook was paid 175. <)d. for a 
 supper to the workmen on finishing their work. 
 Michell could not fail to be interested in the opera- 
 tions, and may quite possibly have been able to give 
 useful help to the designer, as well as to James Essex, 
 the builder of the bridge. 
 
 15 
 
child of Michell, who died about thirty-five 
 years ago, at the age of upwards of eighty, 
 and was intimate with Herschel, that he told 
 her that the principal part of his observations 
 had been made with her father's telescope, 
 which he found more convenient than his 
 own larger one. The Rev. John Michell, I 
 have also been informed, was the inventor of 
 an apparatus for ascertaining the weight of the 
 world, which is known as that of Cavendish 
 I am the grandson of Michell's only daughter, 
 from whom I heard much, and I was also a 
 pupil, more than fifty years ago, of an old 
 clergyman, who had in early life been for 
 several years the curate of Thornhill under 
 Michell. [Signed] Khoda Bux. 
 
 That the memory of the daughter or 
 that of the great-grandson, or of both 
 together, had failed can easily be proved. 
 Some of the statements in the communi- 
 cation are curiously inaccurate. William 
 Herschel undoubtedly passed some of his 
 early years in Yorkshire where he played 
 the hautboy in the band of the Durham 
 militia and performed on the violin at 
 public concerts in Wakefield and Halifax. 
 The family tradition that Michell was 
 16 
 
<c 
 
 no mean violinist' 2 and that he gave 
 musical parties is not improbably true. 
 But it appears to be quite certain that he 
 and Herschel did not make acquaintance 
 with each other in Yorkshire, and that 
 the Rector of Thornhill did not instruct 
 the future illustrious astronomer in the 
 art of grinding specula. Herschel was 
 appointed organist at Bath in the autumn 
 of 1766 and removed to that city at the 
 beginning of the following year, before 
 Michell succeeded to the living at Thorn- 
 hill. There was thus no opportunity for 
 their meeting in Yorkshire. Herschel at 
 Bath was absorbed in his duties as a pro- 
 fessional musician and did not enter upon 
 the study of astronomy till 1773, and next 
 year began to grind specula. The two 
 men had never met nor exchanged letters 
 up to the spring of the year I78I 1 . 
 
 The legend that the discoverer of the 
 planet Uranus received his first lessons in 
 
 1 Scientific Papers of Sir William Herschel (1912), 
 vol. i, p. xxxii. 
 
 C. I 7 
 
telescope construction from the learned 
 Rector of Thornhill must thus be dis- 
 missed as unfounded. Each of these two 
 men of science worked independently 
 and ground his own mirrors. They 
 were first brought into correspondence 
 with each other through the medium of 
 Dr Wm Watson, F.R.S., who, being at 
 Bath and knowing Herschel there, sent 
 to Michell an account of what the astro- 
 nomer had been doing. On 2 1 st January 
 1781, Michell replied: "I look upon 
 myself as very much obliged to you for 
 your favour from Bath, and particularly 
 for the very interesting account, both of 
 what Mr Herschel has done and what 
 he has seen, both of which seem to be 
 very important. I shall be very happy if 
 I should be able to succeed as well, or 
 near as well, as from your account he 
 seems to have done, and I should be very 
 glad of the favour of his correspond- 
 ence : at the same time I think it very 
 probable that I may be more likely to 
 18 
 
learn from him what may be useful to 
 myself, than he to learn anything from 
 me 1 ." A brief correspondence followed 
 between the two astronomers, but they 
 probably met occasionally at the Royal 
 Society's rooms, the table of the Royal 
 Society Club, or other meeting places in 
 London. 
 
 The search for further personal records 
 of the Rector of Thornhill has not been 
 successful. His life in the Yorkshire 
 parish was doubtless quiet and uneventful, 
 full of pastoral duty, well discharged, but 
 with leisure for the prosecution of scien- 
 tific work. This work was undertaken 
 for its own sake, and much of it was pro- 
 bably never published, though it was 
 
 1 Scientific Papers of Sir IVilliam Herschel, vol. I, 
 pp. xxxi, xxxii. The two astronomers never met 
 nor exchanged letters before I2th April 1781, on 
 which date Michell addressed a letter to Herschel 
 dealing with mirrors, and the relative merits of dif- 
 ferent types for large and small apertures. Op. clt. 
 p. xxxii. It is interesting to know, from the testi- 
 mony of Herschel himself, that after Michell's death, 
 he purchased his large telescope. See postca y p. 96. 
 
 '9 
 
always at the service of any fellow-worker 
 interested in the same subjects. Though 
 living so far from London, Michell was 
 nevertheless able to maintain intimate 
 relationship with some of the most emi- 
 nent men of science of his time. He 
 appears to have had some appointment 
 or duty which for a number of years 
 took him annually to London, and gave 
 him the opportunity of attending the 
 meetings of the Royal Society and culti- 
 vating the companionship of his scientific 
 friends. From the year 1758 onwards 
 till towards the close of his life he con- 
 tinued to be a frequent guest at the 
 weekly dinners of the Royal Society Club. 
 There would seem, indeed, to have been 
 a kind of friendly rivalry among the 
 members of the Club in securing him as 
 a guest at these dinners, and in this social 
 competition his friend Henry Cavendish 
 took part. Thus during the summer of 
 1784 he dined seven times with the Club. 
 Two years later, when he spent the 
 20 
 
months of May and June in the Capital, 
 he was a guest every week during his 
 stay, and similar hospitality awaited him 
 at the " Crown and Anchor " tavern as 
 long as he lived 1 . 
 
 During his journeys from and to his 
 Yorkshire home, now by one route, now 
 by another, on horseback or by carriage, 
 or in such public coaches as then plied 
 on the roads between London and the 
 Midlands, Michell appears to have paid 
 close attention to the outcrops and suc- 
 cession of the rock-formations across 
 which he travelled. There was probably 
 no one else so familiar as he with the 
 various quarries, pits and other exposures 
 of these rocks to be seen from the high 
 roads. In the leisurely fashion of those 
 days he would sometimes halt for a night 
 or two on the way, and on these occasions 
 would take advantage of the opportunity 
 of obtaining the evidence to be found in 
 
 1 Annah ef tti Royal Society Club^ pp. 74, 77, 
 165. 
 
 21 
 
any fresh opening of the ground. By 
 these means and by special excursions for 
 the purpose of geological investigation 
 which as we have seen he began to make 
 in his College days, he acquired a broader 
 and more accurate conception of the 
 geological structure of the southern half 
 of England than any of his predecessors. 
 Moreover, his rectory lay in the heart of 
 the great Yorkshire coal-field where the 
 progress of the mining industry continu- 
 ally brought geological questions to his 
 notice. 
 
 It was at Thornhill, during the leisure 
 which his clerical duties permitted, that 
 he was able to carry on those important 
 investigations in physics and astronomy 
 with which his name will always be 
 associated. In the same quiet retirement 
 he devised and constructed the various 
 forms of original and ingenious apparatus, 
 with which he solved or illustrated the 
 problems that presented themselves to his 
 ever active intellect. He continued to 
 
 22 
 
reside at Thornhill till his death on 
 2ist April 1793 in the sixty-ninth year 
 of his age 1 . 
 
 In reviewing the scientific work ac- 
 complished by John Michell it will be 
 convenient to consider it in three sec- 
 tions : first, his contributions to Geology ; 
 second, his contributions to Physics ; and 
 third, his contributions to Astronomy. 
 
 1 MichelFs tombstone at Thornhill records in 
 characteristic eighteenth century language his life, 
 work and character : "In the Chancel of this Church 
 are deposited the Remains of the Rev d . J n . Michell, 
 B.D., F.R.S., and 26 years Rector of this Parish. 
 Eminently distinguished as the Philosopher and the 
 Scholar, he had a just claim to the character of the real 
 Christian, in the relative and social duties of life. 
 The tender Husband, the indulgent Father, the affec- 
 tionate Brother and the sincere Friend were promi- 
 nent features in a character uniformly amiable. His 
 Charities we re not those of Ostentation, but of feeling; 
 His strict discharge of his Professional duties, that 
 of principle, not form. As he lived in possession of 
 the esteem of his Parishioners, so he has carried 
 with him to the grave their regret. He died the 
 21 st April 1793, in the 69* year of his age.*' 
 
I 
 
 CONTRIBUTIONS TO GEOLOGY 
 
 THE subject of the structure of the earth's 
 crust appears to have engaged Michell's 
 attention long before he left Cambridge, 
 though in this as in other investigations, 
 he was in no hurry to publish his obser- 
 vations. He was ultimately led to embody 
 the results of his studies in this subject 
 in the paper on Earthquakes which he 
 communicated to the Royal Society in 
 the spring of the year I76O 1 . This re- 
 markable Essay is not only a dissertation on 
 earthquakes, but contains an exposition 
 of the structure of the terrestrial crust 
 
 1 The full title of this paper was as follows : 
 "Conjectures concerning the Cause, and Observa- 
 tions upon the Phaenomena of Earthquakes ; particu- 
 larly of that great Earthquake of the first of November 
 1755 which proved so fatal to the City of Lisbon, 
 and whose Effects were felt as far as Africa, and more 
 or less throughout almost all Europe ; By the 
 Reverend John Michell M.A. Fellow of Queens' 
 College, Cambridge." It appeared in vol. 51 (1760) 
 of the Philosophical Transactions^ pp. 566-634. 
 
 24 
 
which he had worked out in the course 
 of his journeys and excursions from Cam- 
 bridge over the southern counties of 
 England. As this stratigraphical work 
 was continued through the rest of his life 
 I shall consider it in detail after first 
 dealing with the portion of the paper 
 more immediately concerned with the 
 cause and phenomena of earthquakes. 
 
 i. The Cause and Phenomena of 
 Earthquakes 
 
 The attention of the civilised world 
 was strongly drawn to the long series of 
 earthquakes which culminated in the 
 appalling catastrophe that overwhelmed 
 Lisbon and shook the greater part of 
 Europe on ist November 1755. Many 
 accounts of the facts as well as attempted 
 explanations of them were printed in the 
 current literature of the time. In par- 
 ticular, the Royal Society devoted the 
 forty-ninth volume of the Philosophical 
 Transactions to a large collection of 
 
reports on the subject. By far the most 
 important contribution to the scientific 
 discussion of the nature and cause of 
 these earth-tremors was this paper by 
 Michell. It contained the first attempt 
 to suggest a natural cause of earthquakes, 
 and to explain the nature of seismic 
 movements. 
 
 In attacking the problem Michell 
 started with the fundamental postulate 
 of the existence of " subterranean fires." 
 It was the general belief of the day, which 
 he shared, that these "fires* 3 resulted 
 from the spontaneous ignition of pyritous 
 inflammable strata, such as coals and car- 
 bonaceous shales lying at variable dis- 
 tances beneath the surface of the earth. 
 Werner and his followers were so con- 
 
 . 
 
 vinced that such was the origin of these 
 "fires," to which they attributed the 
 existence of volcanoes, that they believed 
 volcanic action to be of comparatively 
 late date in the history of the globe, seeing 
 that it could not arise till vegetable 
 26 
 
growths had long flourished on the earth 
 and been buried under sediments to be- 
 come beds of coal. Michell argued that 
 if a large body of water should be let 
 down suddenly upon one of these fires 
 a vapour would be produced, the quantity 
 and elastic force of which might be fully 
 sufficient to account for the origin of 
 earthquakes. He pointed out the fre- 
 quency of these concussions in volcanic 
 districts and, like the Wernerian geo- 
 gnosts, he connected the phenomena of 
 volcanoes with the same subterranean 
 fires, the vents and craters marking the 
 position of weaker portions of the outer 
 shell of the earth across which the vapour 
 generated below could force its way to 
 the surface, often carrying with it an out- 
 pouring of molten material. The energy 
 with which this escape was effected 
 appeared to him to be evident from the 
 vast size of the blocks of rock projected 
 during volcanic eruptions and the great 
 distances to which such masses of stone 
 
 27 
 
were often thrown. "If," he asked, 
 "when the vapours find a vent, they are 
 capable of shaking the country to the 
 distance of ten or twenty miles round, 
 what may we not expect from them when 
 they are confined? ' 
 
 He stated that " the motion of the 
 earth in earthquakes is partly tremulous, 
 and partly propagated by waves which 
 succeed one another, sometimes at larger, 
 sometimes at smaller distances, and this 
 latter motion is generally propagated 
 much further than the former 1 ." He 
 believed that both of these motions could 
 be accounted for by the steam generated 
 as assumed. " Let us suppose," he re- 
 marked, " the roof over some subter- 
 raneous fire to fall in. The earth, 
 stones, etc., of which it was composed 
 would immediately sink in the melted 
 matter of the fire below : hence all the 
 
 1 Art. 1 1 of the paper. Michell appears to have 
 been the first to point out that the earthquake travels 
 in successive waves through the earth. 
 
 28 
 
water contained in the fissures and 
 cavities of the part falling in would come 
 in contact with the fire and be almost 
 instantly raised into vapour. From the 
 first effort of this vapour, a cavity would 
 be formed (between the melted matter 
 and superincumbent earth) filled with 
 vapour only, before any motion would 
 be perceived at the surface of the earth : 
 this must necessarily happen, on account 
 of the compressibility of all kinds of earth 
 and stones, etc.; but as the compression 
 of the materials immediately over the 
 cavity would be more than sufficient to 
 make them bear the weight of the super- 
 incumbent matter, this compression must 
 be propagated on account of the elasticity 
 of the earth in the same manner as a pulse 
 is propagated through the air. And 
 again, the materials immediately over 
 the cavity, restoring themselves beyond 
 their natural bounds, a dilatation will 
 succeed to the compression; and these 
 two following each other alternately, for 
 
 29 
 
some time, a vibratory motion will be 
 produced at the surface of the earth. If 
 these alternate dilatations and compres- 
 sions should succeed one another at very 
 small intervals, they would excite a like 
 motion in the air and thereby occasion 
 a considerable noise. The noise that is 
 usually observed to precede or accompany 
 earthquakes, is probably owing partly to 
 this cause, and partly to the grating of 
 the parts of the earth together, occasioned 
 by that wave-like motion before men- 
 tioned " (Art. 6)\ 
 
 " As a small quantity of vapour almost 
 instantly generated at some considerable 
 depth below the surface will produce a 
 vibratory motion, so a very large quantity 
 (whether it be generated almost instantly, 
 or in any small portion of time) will pro- 
 duce a wave-like motion. The manner 
 in which this wave-like motion will be 
 propagated may, in some measure, be 
 represented by the following experiment. 
 Suppose a large cloth or carpet (spread 
 30 
 
upon a floor) to be raised at one edge, 
 and then suddenly brought down again 
 to the floor ; the air under it, being by 
 this means propelled, will pass along, till 
 it escapes at the opposite side, raising the 
 cloth in a wave all the way as it goes. 
 In like manner, a large quantity of vapour 
 may be conceived to raise the earth in 
 a wave, as it passes along between the 
 strata, which it may easily separate in 
 an horizontal direction, there being, as 
 I have said before, little or no cohesion 
 between one stratum and another. The 
 part of the earth that is first raised, being 
 bent from its natural form, will en- 
 deavour to restore itself by its elasticity, 
 and the parts next to it, beginning to 
 have their weight supported by the 
 vapour, which will insinuate itself under 
 them, will be raised in their turn, till it 
 either finds some vent, or is again con- 
 densed by the cold into water, and by 
 that means prevented from going any 
 further" (Art. 58). 
 
 3' 
 
It is thus evident that Michell con- 
 ceived the vapour to continue to force 
 its way onward between the strata as far, 
 at least, as the earthquake continued to 
 be felt at the surface. His familiarity 
 with the regular and gently inclined 
 stratification of the rocks in the southern 
 part of England, and his experience that 
 at the surface of the ground they may 
 for the most part be easily split open 
 along their bedding-planes led him to 
 this belief. He imagined that the vapour 
 might be propelled even to the extreme 
 limits of the area affected by an earth- 
 quake, for he remarks in one place that 
 " the shortest way that the vapour could 
 pass from Lisbon to Loch Ness was under 
 the Ocean" (Art. 98 note). 
 
 The same ingenious paper showed how 
 the centre or focus from which an earth- 
 quake is propagated may be ascertained 
 first, from observation of the different 
 directions from which the shock arrives 
 at several distant places : " if lines be 
 32 
 
drawn in these directions the place of 
 their common intersection must be nearly 
 the place sought"; secondly, from the 
 time of arrival of the earthquake at 
 different places; and thirdly, from the 
 successive arrivals of the great sea-wave. 
 The greatest degree of exactness is ob- 
 tainable " in those cases where earth- 
 quakes have their source from under the 
 ocean, for the proportional distance of 
 different places from that source may be 
 very nearly ascertained by the interval 
 between the earthquake and the succeed- 
 ing wave : and this is the more to be 
 depended on, as people are much less 
 likely to be mistaken in determining the 
 time between two events, which follow 
 each other at a small interval, than in 
 observing the precise time of the happen- 
 ing of some single event" (Arts. 9093). 
 By way of example, the author, making 
 use of his three indications of origin, 
 computed that the focus of the Lisbon 
 earthquake lay under the Atlantic Ocean, 
 c. 33 
 
at the distance of a degree of a great 
 circle from Lisbon, and a degree and 
 a half from Oporto. 
 
 With singular prescience he believed 
 that probably earthquakes are not of 
 comparatively deep-seated origin a con- 
 clusion which is now generally held by 
 seismologists. He was well aware that 
 data were then wanting on which to base 
 any satisfactory estimate as to the depth 
 of the focus, which might vary con- 
 siderably, but he thought that " some 
 kind of guess might be formed concerning 
 it." Hazarding what he called "a ran- 
 dom guess," he believed that the depth 
 at which the impulse of the Lisbon 
 earthquake started, " could not be much 
 less than a mile or a mile and a half, and 
 probably did not exceed three miles." 
 
 In considering the merit of Michell's 
 Earthquake paper as a contribution to 
 science we must remember that he him- 
 self modestly offered it as pretending to 
 be no more than " conjectures." That so 
 34 
 
many of his "conjectures" and "guesses" 
 have been confirmed in later stages of the 
 progress of science is a striking proof of 
 his rare genius. He accepted the current 
 doctrine of the day regarding the existence 
 and nature of " subterraneous fires." 
 That doctrine has long been exploded. 
 The general high temperature of the 
 deeper parts of the earth's crust has been 
 proved by abundant evidence, though the 
 problem of the cause of this internal heat 
 cannot yet be regarded as solved. 
 
 It seems not improbable that some of 
 the earthquakes in volcanic regions may 
 be produced, as Michell suggested, by 
 the sudden descent of quantities of sur- 
 face water upon the molten magma below. 
 Extinct craters are apt to become lakes or 
 tarns by gathering into their basins the 
 results of the atmospheric precipitation 
 of moisture. The sudden collapse of the 
 floor of one of these craters, filled in this 
 way, and the descent of a large body of 
 water upon molten lava below would 
 
 35 
 
conceivably give rise to a minor earth- 
 quake. Michell therefore suggested what 
 may be a vera causa in volcanic areas. 
 
 Although his conjecture that the travel- 
 ling of the earthquake waves along the 
 surface of the earth is due to the propul- 
 sion of concomitant waves of vapour 
 between the strata underneath, has never 
 been accepted, we should remember that 
 it included the first recognition or at least 
 premonitory suggestion of the potency of 
 highly heated aqueous vapour as a sub- 
 terranean dynamical agency in geological 
 operations. Whether, if suddenly gene- 
 rated at a local centre, in the manner he sup- 
 posed, superheated steam could force its 
 way between the strata for some distance, 
 as he imagined, may be doubted. But 
 since his time, and in a manner never 
 dreamt of by Michell, aqueous vapour has 
 been ascertained to play a stupendous part 
 in volcanic activity. We now know that 
 the internal magma which underlies vol- 
 canic regions contains a vast volume of 
 36 
 
aqueous and other vapours which are held 
 absorbed or dissolved in its molten mass 
 under the immense pressure that pre- 
 vails deep below the surface. When this 
 pressure is lessened as the lava mounts 
 in the throat of a vent, the imprisoned 
 vapours escape with explosive violence, 
 blowing the liquid material into the 
 finest dust, which may fill the air and 
 darken the sky over a wide stretch of 
 country, while at the same time the still 
 steaming lava may issue incopiousstreams 
 from the crater. Moreover, geologists 
 have long been familiar with the fact that 
 besides being erupted at the surface by 
 the enormous expansive force of these 
 absorbed vapours, the magma has in 
 many places forced its way horizontally 
 through the terrestrial crust, often be- 
 tween the planes of stratification, over 
 wide areas and for long distances. The 
 Intrusive Sheets or Sills, so abundant in 
 the British Isles, dating from Archaean 
 time up to that of the Tertiary basalt- 
 
 37 
 
plateaux, are stupendous monuments of 
 the part which the propulsive force of 
 the vapours in the subterranean magma 
 has played in the past history of the 
 globe. The most noted of them, the great 
 Whin-Sill of the north of England, 
 averages from 80 to 100 feet in thickness 
 and has been injected, possibly at successive 
 intervals, between and across the Car- 
 boniferous strata, over an area of probably 
 not less than 1000 square miles. With 
 what type of earthquake the extravasation 
 of such great sheets of molten material 
 would be accompanied may be left to the 
 imagination. 
 
 It is remarkable that John Michell, 
 who recognised the influence of elastic 
 compression in generating the vibratory 
 movement in an earthquake, should not 
 have advanced still farther, and have per- 
 ceived that the explosive shock to which 
 he attributed the earthquake must of 
 itself give rise to a wave of elastic com- 
 pression in the earth, which starting out 
 38 
 
in all directions may travel thousands of 
 miles before becoming so feeble as to be 
 no longer sensible to ordinary observation. 
 
 n. The Structure of the Stratified Part 
 of the Earth's Crust 
 
 The most important part of Michell's 
 Earthquake paper, considered as a land- 
 mark in the history of geological science, 
 is the account which it contains of what 
 is now known as "the crust of the Earth." 
 Earlier in the century John Strachey 1 
 had shown that in the south-west of Eng- 
 land the materials of the visible part of 
 the earth had not been promiscuously 
 accumulated, but had been laid down in 
 a recognisable succession which he traced 
 in due order from the Coal up to the Chalk. 
 He further perceived that while the coal 
 strata are all more or less inclined, their 
 upturned edges are overlain by the Red 
 Marl and later formations in horizontal 
 
 1 Phil. Tram. vol. 30 (1719), p. 968; vol. 31 
 
 (1 7*5), P- 395- 
 
 - 
 
 39 
 
beds. Michell's observations, which were 
 all made previous to 1760, when his paper 
 appeared, carried the subject considerably 
 further. It must be remembered that the 
 importance of organic remains in strati- 
 graphy was still unknown. Indeed, there 
 were probably naturalists still surviving 
 who, if they did not regard these remains 
 as "sports of nature," firmly believed 
 them to be memorials of Noah's Flood, 
 during which the whole vast thickness 
 of stratified formations was supposed to 
 have been deposited. Even such a shrewd 
 observer as John Woodward, founder of 
 the Chair of Geology at Cambridge, enter- 
 tained this belief, and thought that the 
 fossils had arranged themselves according 
 to their weight, the heavier shells and 
 bones sinking into the deeper parts of the 
 sediments in the diluvial waters, while 
 the lighter organisms settled down in the 
 upper layers. 
 
 Over the whole of the region in the 
 south of England which he was able 
 40 
 
personally to examine Michell found that 
 the rocks everywhere displayed a striking 
 order and regularity. The earth, he wrote, 
 "is not composed of heaps of matter 
 casually thrown together, but of regular 
 and uniform strata. These strata, though 
 they frequently do not exceed a few feet, 
 or perhaps a few inches, in thickness, yet 
 often extend in length and breadth for 
 many miles, and this without varying 
 their thickness considerably. The same 
 stratum also preserves a uniform character 
 throughout, though the strata imme- 
 diately next to each other are very often 
 totally different. Thus, for instance, we 
 shall have, perhaps, a stratum of potter's 
 clay ; above that a stratum of coal ; then 
 another stratum of some kind of clay ; 
 next a sharp grit-sandstone ; then clay 
 again ; and coal again above that ; and 
 it frequently happens that none of these 
 exceeds a few yards in thickness. There 
 are, however, many instances, in which 
 the same kind of matter is extended to 
 
the depth of some hundreds of yards ; 
 but in all these, a very few only excepted, 
 the whole of each is not one continued 
 mass, but is again subdivided into a great 
 number of thin laminae, that seldom are 
 more than one, two or three feet thick, 
 and frequently not so much " (Art. 38). 
 This careful observer next describes 
 with minute precision the system of per- 
 pendicular fissures (or what are known as 
 joints) by which the stratified rocks are 
 so abundantly traversed. He notices the 
 frequent bent position of the strata, and 
 shows that their inclination increases as 
 they are traced towards the mountains, 
 which are generally, if not always, formed 
 out of the lower, and therefore older rocks. 
 He illustrates the subject by the follow- 
 ing experiment. "Let a number of 
 leaves of paper, of several different sorts 
 or colours, be pasted upon one another : 
 then bending them up together into a 
 ridge in the middle, conceive them to be 
 reduced again to a level surface by a plane 
 42 
 
so passing through them, as to cut off all 
 the part that had been raised ; let the 
 middle now be again raised a little, and 
 this will be a good general representation 
 of most, if not of all mountainous coun- 
 tries together with the parts adjacent, 
 throughout the whole world " (Art. 43). 
 
 This simple but ingeniously contrived 
 model indicates how clearly its author 
 had grasped some of the main facts which 
 modern geology has brought to light. 
 Thus he recognised that the sequence of 
 stratified formations has occasionally been 
 interrupted by upheavals whereby, along 
 certain lines of elevation, these formations 
 have been exposed to the action of the 
 various denuding forces of nature by 
 which, if the denudation continued long 
 enough, the upraised tract would be re- 
 duced approximately to a plane, on which 
 any subsequent deposits would, in modern 
 phrase, lie unconformably. 
 
 From this arrangement of the stratified 
 part of the earth's crust, as he points out, 
 
 43 
 
" we ought to meet with the same kinds 
 of earths, stones and minerals, appearing 
 at the surface in long narrow slips, and 
 lying parallel to the greatest rise of any 
 long ridges of mountains ; and so in fact 
 we find them." He remarks that in Great 
 Britain, the main trend of the outcrops 
 runs nearly north by east and south by 
 west. He notes also that in the course of 
 the earth-movements to which the terres- 
 trial crust is subject, the strata have not 
 escaped rupture. " The whole set of 
 strata on one side of a cleft are sunk down 
 below the level of the corresponding 
 strata on the other side," and he saga- 
 ciously adds that, " if in some cases this 
 difference in the level of the strata on the 
 different sides of the cleft should be very 
 considerable, it may have a great effect 
 in producing some of the singularities of 
 particular earthquakes" (Arts. 44, 50). 
 
 It should be remembered that all the 
 geological observations by John Michell 
 referred to in the foregoing pages were 
 44 
 
made by him during his residence at 
 Cambridge ; therefore before the spring 
 of the year 1 760 when his Earthquake 
 paper was presented to the Royal Society. 
 He never published any further contri- 
 butions to geology. It has not unnaturally 
 been inferred that he abandoned that 
 branch of science, in order to devote him- 
 self to the severer studies of which the 
 fruits were given in his subsequent papers. 
 But the truth is that his interest in geo- 
 logical questions remained unabated to 
 the end. Proof of this continued zeal is to 
 be found in a long letter of the year 1788, 
 hitherto unpublished, written by Michell 
 to Henry Cavendish, which has fortu- 
 nately been preserved among the papers 
 of that great philosopher. It vividly in- 
 dicates how keenly its writer, in his 
 journeys to and from London, kept him- 
 self on the watch for any fresh pit, 
 quarry or other exposure of the rocks 
 below the surface. 
 
 It appears that Cavendish, for some 
 
 45 
 
years between 1783 and 1793, was in 
 the habit of making excursions with 
 Dr Charles Blagden, for the purpose of 
 tracing the succession and distribution of 
 the strata that underlie the southern 
 counties of England. Of these "Jour- 
 neys," as he called them, he made notes, 
 which have been preserved. The Caven- 
 dish MSSl, at the instance of the Cam- 
 bridge University Press, have been placed 
 by the Duke of Devonshire in the hands 
 of Sir T. Edward Thorpe, with a view 
 to the publication of the chemical papers 
 which they include. The collection of 
 manuscripts contains the letter from 
 Michell, together with the draft of 
 Cavendish's reply. This correspondence, 
 which throws an interesting light on the 
 condition of geological science in this 
 country during the last quarter of the 
 eighteenth century, is now published for 
 the first time 1 . 
 
 1 Dr (afterwards Sir) Charles Blagden, who be- 
 came one of the Secretaries of the Royal Society in 
 
Michell to the Hon. Henry Cavendish 
 
 [I4TH AUGUST, IjSS] 
 
 Dear Sir 
 
 Some observations, as I returned 
 from London, having occur'd to me 
 with regard to the Northamptonshire, 
 Lincolnshire, &c. yellow limestone (viz 
 Dr Blagden's, not my yellow limestone) 
 I take the liberty of communicating them 
 to you, though perhaps hardly worth 
 your attention. I could, indeed, have 
 wished, I had been able to give them 
 you with more precision. I lodged one 
 night, in my road, at the Royal Oak, 
 a new house built on Greetham Common, 
 
 1784, appears to have acted as assistant or secretarial 
 friend to Cavendish, who settled an annuity upon 
 him and left him a handsome legacy. The MS. 
 of the Journeys contains the joint observations made 
 by the two coadjutors. It will be seen from Michell's 
 letter that he was able to set them right on at least 
 one important point, and that Cavendish acknow- 
 ledged the correction in his reply. As already men- 
 tioned, Michell's letter has been alluded to in 
 Wilson's Life of Cavendish^ pp. 129, 177. 
 
 47 
 
about 7 or 8 years ago, 96 miles from 
 London, which is in the midst of that 
 set of strata, which constitute the Yellow 
 Limestone l . When walking in the garden 
 there, I unexpectedly found it to be upon 
 clay 2 , and enquiring of the master of the 
 house about it, I found that he had been 
 obliged to sink a ditch, between three 
 and four feet deep, at one side of his 
 garden, as well as to make two or three 
 drains of about the same depth to carry 
 the water into it, in order to prevent it 
 from being so swampy as to be unfit for 
 that purpose ; and the water at that time 
 stood some inches deep in some parts of 
 the ditch, though it was in the most 
 droughty part of that time when every- 
 thing about London was so much burnt 
 up, which was also the case in a good 
 
 1 [Apparently a name for the limestones of the 
 Lower Oolite group.] 
 
 2 [There can be little doubt that this was a 
 portion of the " chalky boulder-clay " of the district, 
 lying unconformably upon the various Jurassic rocks, 
 and enclosing flints, bits of coal and many other 
 materials from northern sources.] 
 
measure, though not quite so much so, 
 about Greetham. I the less expected 
 to find things in this state, the land 
 hereabout not being low, and having 
 a moderate declivity, sufficient, I should 
 have thought, if it had not been retained 
 by the clayey ness of the soil, to have 
 carried off the water even of a wet season. 
 I also observed lying about two or 
 three small heaps of pebbles, among which 
 were some flints ; and enquiring of the 
 master of the house, whence they came, 
 he informed me that they were pick'd 
 up from the plough'd fields, which con- 
 sisted of the same clay with the garden : 
 they were lodged, as I understood, 
 amongst the clay, being found here and 
 there in digging into it. It was not until 
 after you and Dr Blagden mention'd your 
 having seen some specimens of chert, at 
 some place on the coast, I think, amongst 
 this set of strata, that I was aware that 
 any flints were ever found belonging 
 to them, and the flints I met with at 
 c. . 49 
 
Grectham Common, must, I suppose, be 
 of the same kind with those you con- 
 sider'd as chert, though I should rather 
 consider them as flints ; for though they 
 are opake and had nothing of that horny 
 look, when broken, that the flints from 
 the chalky countries have, yet they have 
 more of the glassy texture, and want 
 that appearance of toughness, which the 
 cherts in general have, so that I should 
 not hesitate to call them flints rather than 
 cherts. At the same time, I can easily 
 conceive that our ideas of them may not 
 so far coincide, but that you might well 
 enough look on them as belonging to the 
 cherts. I however met with, amongst 
 the rest, two or three flints that every- 
 body must look on as such, being, when 
 broken, black and horny, and as perfect 
 as the most perfect of the chalk country 
 flints ; they were also roundish like those, 
 and were cover'd with a dark brown 
 coat ; whereas the others had no coat, 
 nor any appearance of ever having had 
 50 
 
one, that I could see, being rather angular 
 and somewhat irregularly shaped. 
 
 My landlord also told me, he had been 
 informed (for he had only kept the Inn 
 a year or two himself) that, when the 
 house was built, they had sunk a Well 
 nine yards deep through this bed of clay, 
 before they came to the stone ; the clay 
 may therefore, when compleat, very 
 possibly have been of still greater thick- 
 ness, but I had no opportunity of learning 
 any further particulars about it. My 
 Landlord also informed me, that he had 
 been told that in sinking the above Well, 
 they had met with in the clay a few 
 small stragling bits of coal, but nothing, 
 as far as he could make out, from the 
 vague account he had been able to pro- 
 cure, and which came through three or 
 four hands, that seem'd to have any ten- 
 dency towards a regular stratum. This 
 story, however, seems to have induced 
 the owner of the estate (Lord Winchelsea, 
 I think), to try for coal somewhere there- 
 
 5' 
 
abouts ; for he had had people to bore in 
 search of it, and they had gone to the 
 depth of 130 yards without any success, 
 as I could easily conceive. 
 
 This clay did not seem to compose a 
 very uniform stratum, not only consisting 
 of harder and softer parts, but having 
 likewise those flints and pebbles scatter'd 
 through it, in such manner, if I conceived 
 rightly of the matter, as to shew that 
 though they might perhaps have been 
 formed in it originally, yet supposing 
 this to be the case, they must, however, 
 have been somewhat disturbed from their 
 places after their formation, though I 
 neither saw nor could learn circumstances 
 sufficient to form any probable guess con- 
 cerning the way in which these flints, as 
 well as the other pebbles, which seem'd 
 to contain sand and iron in their com- 
 position, were formed. May I not how- 
 ever, consider the circumstances and 
 
 
 
 company in which they are found as 
 rather tending to strengthen my con- 
 
 52 
 
jecture concerning the origin of flints in 
 general 1 ? 
 
 Besides this bed of clay, of the existence 
 of which I was not aware before my last 
 return from town, there is another pretty 
 considerable bed of clay (for I think it is 
 not the same appearing again at another 
 place) which I have often taken notice 
 of, that shows itself in the side of the 
 hill immediately descending towards 
 Grantham, on the east side of it 2 . What 
 is the thickness of this bed I don't know, 
 but from what I have been able to learn 
 concerning it, I should suppose it is not 
 less than the other. There are also found 
 in it, in one part of the stratum, some 
 Cornua ammonis^ and in another part some 
 selenites ; but these last I pay no great 
 regard to, as they are frequently of a very 
 
 1 [It would have been interesting to know what 
 this conjecture was. How great would have been 
 A lie he IPs astonishment could it then have been 
 revealed to him what is now known about the history 
 of the Boulder-clay which he here describes so 
 minutely.] 
 
 1 [Probably one of the clays of the Upper Lias.] 
 
 53 
 
modern origin, being commonly found 
 in clay, where some vitriolic water oozes 
 or trickles out, provided there is a little 
 calcareous matter likewise for it to unite 
 with. There are a great many Bricks and 
 Tiles made out of this clay for the use of 
 the town of Grantham ; and I imagine, 
 what might otherwise be very well, 
 I think, supposed to be the case, that it 
 is not an accidental mass of clay in that 
 place only \ but part of a stratum of some 
 extent, for I observed some other Brick- 
 kilns, at a mile or two distance, on the 
 side of a hill, at about the same level. 
 Whether there may not be still more 
 beds of clay in some other parts of this 
 set of strata, I don't know, though from 
 these instances and general analogy, it is 
 not very unlikely there should. Almost 
 immediately to the westward on this side 
 Grantham 2 , we again have clay, which is 
 
 1 [Like the tract of Boulder-clay above de- 
 scribed.] 
 
 8 [The rock formations to the west of Grantham 
 
 54 
 
continued to the top of Gunnerby Hill, 
 but which, however, must no doubt con- 
 sist in great part of some kind of stone ; 
 for it could not otherwise rise so much 
 as it does in so short a space, viz 70 or 
 80 yards perpendicular, I apprehend, in 
 the distance of a little more than a mile. 
 There is likewise another set of strata 
 which form another ridge of lower hills, 
 three or four miles nearer this way, about 
 Foston ; all these probably contain several 
 beds of clay and under these are found the 
 Lyas, which consists of a great many 
 alternate beds of clay and blue limestone. 
 I believe I have formerly mentioned 
 it to yourself and Dr Blagden, but not 
 recollecting whether I have before insisted 
 so much upon it, as I might have done, 
 I shall take this opportunity, which the 
 country I have just been mentioning 
 suggests, of observing, that to the west- 
 ward of all that edge of Dr Blagden's 
 yellow limestone, next our side of the 
 
 consist of what are now known as the Upper, Middle 
 and Lower Lias.] 
 
 55 
 
sets of strata which run from north to 
 south through the island of Great Britain, 
 as far as I am acquainted with them, lies 
 the Lyas at no very great distance ; 
 though, indeed, with two or three sets 
 of strata, viz those of Gunnerby and 
 Foston, between them ; these run into 
 Leicestershire to the south, and to where 
 the Trent falls into the Humber, and the 
 upper part of the Humber to the north, 
 the Lyas being the lowest of all these 
 sets of strata, and all of them lying below 
 the yellow limestone 1 in order, but 
 nowhere having any coal near them ; 
 whereas our yellow limestone 2 has no 
 Lyas anywhere under it or near it to the 
 westward of it, but on the contrary, 
 everywhere coal very near the western 
 edge of it, all the way from Leicestershire 
 by the edge of Nottinghamshire and 
 Derbyshire, and a long way into York- 
 
 1 [Now known as the group of Lower Oolites.] 
 
 1 [That is, the Magnesian Limestone of the 
 
 Permian system which stretches as a broad band 
 
 from near Nottingham to the mouth of the Tyne, 
 
 a distance of 1 50 miles.] 
 
 56 
 
shire, and how much further I don't for 
 certain know ; and in many places, if not 
 everywhere, the coal is found under our 
 yellow limestone, through which they 
 sink in many places in order to come at it. 
 Since I began to write this letter I 
 received from M r Beatson of Rotheram, 
 a parcel of the substance he was mention- 
 ing to you. He sent, by the person who 
 brought it to me, an apology for not 
 having sent it before, and saying at the 
 same time that it was not yet so good 
 a specimen as he had wished to have sent. 
 As it was directed to me, though it ought 
 perhaps rather to be considered as your 
 property, I have taken the liberty of 
 reserving the half of it for myself, which, 
 however, if you want any more than 
 I have sent you, either to make experi- 
 ments upon, or for any other purpose, 
 I will send you whenever you please. It 
 seems to be in general a good deal harder 
 than the black lead used for pencils, 
 though some of the thin flakes seem to 
 mark pretty well ; probably the difference 
 
 57 
 
may be owing to too large a quantity of 
 Iron contained in it ; for it appears by it's 
 applying so very strongly as it does to 
 the magnet, to contain a great proportion 
 of that metal. 
 
 With best respects to yourself and due 
 comp s to all friends when you see them, 
 particularly those of the " Crown and 
 Anchor" and "Cat and Bagpipes" clubs 1 , 
 I am, Dear Sir 
 
 Your obed' humble servant 2 
 
 J. MICHELL 
 
 THORNHILL, 14 Aug 1788 
 
 1 The Crown and Anchor Tavern, Strand, as 
 already mentioned, was the meeting place of the 
 Royal Society Club at this time and continued to 
 be so for sixty-eight years, from 1780 to 1848. 
 Reference has been made (p. 20) to MichelPs frequent 
 appearance at the Club, where he constantly met 
 Cavendish. The "Cat and Bagpipes" was "a 
 public house of considerable notoriety, with this 
 sign. It existed at the corner of Downing Street, next 
 to King's Street. It was also used as a chop-house, 
 and frequented by many of those connected with the 
 public offices in the neighbourhood " (Notes and 
 Queries, Nov. 9, 1850, p. 397). But nothing seems 
 to be known of the Club to which Michell refers 
 as meeting there. 
 
 * This deferential expression, so characteristic 
 
 58 
 
Along with this letter therehas been pre- 
 served among the Cavendish papers the 
 rough draft of the reply to it sent by the 
 philosopher, which is chiefly interesting 
 as an example of the detailed examination 
 which Henry Cavendish continued for 
 some years to bestow upon the sequence 
 and distribution of the geological forma- 
 tions of the southern half of England. 
 With only lithological characters as a 
 guide, he could hardly fail to make 
 mistakes in the order of superposition. 
 
 " I am obliged to you and M r Beatson 
 for the plumbago and to you for your 
 letter. 
 
 I have got some which I received from 
 Wales, part of which, I think, is purer 
 than M r Beatson's. But the rest consists 
 of flakes of a more sparkling nature than 
 Beatson's and less disposed to mark paper. 
 I have also some which I received under 
 
 of the period, was the usual manner in which Michell 
 ended his letters to Cavendish. It is found in the 
 original of his paper of 26th May 1783, which is 
 printed in Phil. Tram. vol. 74 (1784), p. 35. 
 
 59 
 
the name of sulphur-iron, and which is 
 much the same to appearance as the latter 
 part of the Welsh specimen. I analysed 
 this and found it to contain more siliceous 
 earth than plumbago, besides a good deal 
 of iron, not so much in the state of plum- 
 bago but what it would dissolve in acids. 
 
 I suppose it must be the yellow lime- 
 stone about Bridport in which Dr Bl. 
 told you we found chert. How far it de- 
 serves that name I can not say, but to 
 the best of my remembrance it was of a 
 much coarser grain, and had not at all the 
 appearance of flint ; but my memory is 
 too imperfect for me to attempt to de- 
 scribe it to you. As the circumstances 
 relating to it are rather remarkable, I will 
 mention what we saw of it last year. 
 
 On descending the chalk hills between 
 Dorchester and Bridport, by the time 
 we got about ^ way to the bottom, we 
 came to the yellow limestone, which 
 seemed separated from the Chalk only by 
 a stratum of clay of no great thickness. 
 60 
 
A few miles farther, the stone, though to 
 appearance much the same, was found to 
 be of a siliceous nature, with very little 
 calcareous matter in it. At Lyme the cliffs 
 are blue clay and blue Lyas ; but the top 
 of the hill, which we pass over imme- 
 diately before we come to Lyme, consists 
 of gravel composed of this chert ; and 
 about a mile to the west of Lyme was a 
 hill with a steep bank towards the sea, 
 the foot of which was blue Lyas with 
 yellow limestone over it, mixed with 
 veins of this chert, so much like limestone 
 that one could hardly distinguish them 
 by the eye ; but it must be observed that 
 this, as well as most of the limestone we 
 saw, is of a hard compact and rather brown 
 kind. 
 
 From hence to Sidmouth the soil con- 
 sisted chiefly of this cherty gravel, but the 
 cliffs on each side of Sidmouth consisted 
 of red rock (the sandy kind consisting of 
 thick strata) ; only on the east side they 
 were covered with a great thickness of 
 
 61 
 
the same chert-gravel as the hill by Lyme. 
 From hence we had red rock and red soil, 
 without any chert-gravel to Halldown 
 [Haldon], which is a hill extending from 
 a little to the west of Exeter to near 
 Teignmouth. The upper part of this hill 
 consisted of the above-mentioned chert- 
 gravel, so that it appears that the lime- 
 stone of this country is very much mixed 
 with chert, a great deal of which seems 
 to have been reduced to gravel and de- 
 posited on strata of older formation, at a 
 great distance from the limestone where 
 it was formed. Besides, Halldown, the 
 top of which is covered with this matter, 
 is, I believe, entirely separated from the 
 rest of the country by a broad tract of the 
 red-rock country. In the cliffs between 
 Minehead and Watchett, I saw the red- 
 rock lying immediately under the blue 
 Lyas. 
 
 In digging the tunnel for the canal in 
 Gloucestershire, they have found one or 
 more beds of clay between the strata of 
 
 62 
 
yellow limestone, and I believe the Chalk 
 is not free from them. A little to the 
 west of D unstable considerable springs 
 of water break out on the N.W. side 
 of the Chalk hills, about the level of Dun- 
 stable. 
 
 I believe you must be right in sup- 
 posing your yellow limestone to be quite 
 distinct from the other. From what I 
 can learn, I believe the N.W. edge of 
 the other, after running from Gunnerby 
 Hill on the E. side of the Trent, crosses 
 the H umber and runs under the Yorkshire 
 Chalk, and appears again about Castle 
 Howard, and so runs to Scarborough, the 
 Chalk in that place lapping over and ex- 
 tending further west than the limestone 1 ." 
 
 This letter furnishes an example of the 
 detailed manner in which Cavendish con- 
 ducted his "Journeys." It contains several 
 
 1 The last page and a half of this draft-letter 
 consists of an account of a journey made by Dr 
 Blagden from Dieppe to Paris, with details of his 
 observations on the geological features of the region 
 through which he passed. 
 
 63 
 
 
interesting original observations. Of 
 these the most remarkable is that which 
 recognised the important overlap of the 
 Cretaceous series of Yorkshire whereby 
 almost the whole of the underlying 
 Jurassic formations are concealed for a 
 space of some twenty miles a feature in 
 the geological structure of the country 
 of which the full import was not under- 
 stood for many years after his time. He 
 evidently accepted Michell's opinion that 
 the yellow limestone which immediately 
 overlies the Coal-measures of Derbyshire 
 and Yorkshire could not be the same as 
 that which overlies the Lias, but must 
 belong to a lower platform in the suc- 
 cession of formations. 
 
 In the course of years, with his eyes 
 constantly on the alert for fresh light on 
 geological questions, Michell made many 
 original observations that well deserved to 
 be published, but with characteristic 
 modesty he refrained from putting them 
 in print. At the same time, as in his 
 
 64 
 
correspondence with Priestley and with 
 Cavendish, he was ready to communicate 
 them to any enquirer who took an interest 
 in the subject. By a happy accident one 
 of these communications to a friend, was 
 committed by this friend to writing and 
 was published seventeen years after 
 Michell had passed away. In August 
 1 8 1 o there appeared, in the Philosophical 
 Magazine, a letter from John Farey, Sen., 
 a well-known geologist of the day, enclos- 
 ing certain notes made by John Smeaton, 
 the eminent engineer, and endorsed by 
 him as " Mr Michell's account of the 
 south of England strata." Farey states 
 that this account was probably made 
 verbally by Michell to his friend Smeaton, 
 very soon after November 1788, and was 
 taken down by Smeaton " on the cover 
 of a recent letter as being the only piece 
 of paper then at hand ; for Mr Smeaton 's 
 decease in 1792 shows that it must have 
 been prior to that time/' The document 
 was as follows : 
 
 G. 65 
 
Yards 
 
 Chalk 120 
 
 Golt 50 
 
 Sand, of Bedfordshire 10 or 20 
 
 Northampton lime and Port- 
 land limes lying in several 
 strata 100 
 
 Lyas strata 70 or 100 
 
 Sand, of Newark about 30 
 
 Red ClayofTuxford 100 
 
 Sherewood Forest, pebbles and 
 
 gravel 50 unequal 
 
 Yery fine white sand uncertain 
 
 Roch Abbey and Brotherton 
 
 limes 100 
 
 Coal strata of Yorkshire l ... 
 
 Farey, in communicating this Table, 
 remarked that the " account of the strata 
 imperfect as it is, shews that Mr Michell 
 was acquainted with the principal features 
 of the south of England strata, at an 
 earlier period than anything that has been 
 published on the subject." He adds as 
 
 1 The Northampton limestone belongs to the 
 Inferior Oolites, and the Portland limestone to the 
 Upper Oolites ; they both lie above the Lias as shown 
 in the Table. The Keuper and Bunter divisions 
 of the Trias are here correctly placed between the 
 Lias and the Permian Magnesian Limestone. 
 
 66 
 
specially remarkable that Michell should 
 have correctly applied to the strata be- 
 tween Grantham and Balderton the ap- 
 pellation of Lyas, a term not then known 
 or in use nearer than Gloucestershire or 
 Somersetshire, showing that this saga- 
 cious observer " had contemplated the 
 identity of the British strata over wide 
 spaces." 
 
 Few men, unless they chance to be ex- 
 perienced field-geologists, can fully appre- 
 ciate the amount of time, skill and labour 
 which the construction of this Table of 
 Strata required. It must represent the 
 result of the journeys of many years over 
 a large part of the southern half of Eng- 
 land. It implies an infinite patience and 
 no little lithological deftness in correlat- 
 ing the petrographical characters of the 
 various strata, with such success as to be 
 able to identify the different members at 
 distant parts of their outcrop. The key 
 furnished by organic remains to the 
 chronological sequence of the formations 
 
 67 
 
had not yet been discovered by William 
 Smith, who, born two years after MichelFs 
 transference to Thornhill, did not begin 
 to publish his epoch-making discovery 
 until the distinguished Rector had passed 
 away. That the Table given above should 
 be imperfect and in some particulars in- 
 accurate does not derogate from the 
 author's credit and originality. He un- 
 questionably established the succession of 
 the main subdivisions of the English 
 Mesozoic formations, and he did this by 
 laborious determinations of the order of 
 superposition and the identity or close 
 resemblance of mineral characters over a 
 wide region, without any help from pa- 
 laeontological evidence. 
 
 Though students of the history of 
 geological discovery in England have 
 been acquainted with MichelTs work and 
 have sometimes expressed their high 
 sense of its value, there is reason to think 
 that the pioneer merit of his contributions 
 to geology has never yet been adequately 
 68 
 
recognised. Lyell indeed has referred to 
 his "original and philosophical" views 
 on earthquake phenomena and has de- 
 clared that "some of his observations 
 anticipated in so remarkable a manner the 
 theories established forty years afterwards, 
 that his writings would probably have 
 formed an era in the science, if his re- 
 searches had been uninterrupted. He 
 held, however, his professorship only 
 eight years 1 , when hiscareer was suddenly 
 cut short by preferment to a benefice. 
 From that time he appears to have been 
 engaged in his clerical duties, and to have 
 entirely discontinued his scientific pur- 
 suits, exemplifying the working of a 
 system still in force at Oxford and Cam- 
 bridge, where the chairs of mathematics, 
 natural philosophy, chemistry, botany, 
 astronomy, geology, mineralogy and 
 others, being frequently filled by clergy- 
 men, the reward of success disqualifies 
 
 1 His tenure of the office, as already shown, was 
 ess than two years. 
 
 6 9 
 
them, if they conscientiously discharge 
 their new duties, from further advancing 
 the cause of science, and that, too, at the 
 moment when their labours would natur- 
 ally bear the richest fruits 1 ." 
 
 The statement in this quotation that 
 from the time of his entering upon his 
 clerical duties, Michell " appears to have 
 entirely discontinued his scientific pur- 
 suits " was doubtless based on the fact 
 that after the appearance of his Earth- 
 quake paper he never published any fur- 
 ther contribution to geological science. 
 We may well believe that his clerical 
 duties were always conscientiously and 
 zealously discharged. But up till near the 
 close of his life he never ceased to pursue 
 his scientific studies. In regard to his 
 geological proclivities we have seen that 
 so far from abandoning that subject he 
 
 1 LyelPs Principles of Geology^ Tenth Ed. vol. i, 
 p. 61. To this testimony should be added that of 
 Fitton, Phil. Mag. 1832, I, p. 268: K. A. von Zittel, 
 Geschichte der Geologie (1899), pp. 8l, 157. Michell 
 is included in the author's Founders of Geology^ 1897. 
 
 70 
 
continued to prosecute it with a breadth, 
 originality and success which show him 
 to have been the most accomplished Eng- 
 lish geologist of his time. He was in no 
 hurry to publish his observations though 
 ever willing to communicate them to his 
 friends, and they have come to light al- 
 most by accident since his death. He 
 well deserves to be ranked as one of the 
 founders of Geology in England. 
 
 But his "scientific activities, extending 
 beyond the geological sphere, ranged 
 far and wide through the physical 
 sciences, and his leisure hours at Thorn- 
 hill were largely devoted to personal 
 research and experiment in that wide 
 domain. Probably a good deal of his 
 original work was never published, but 
 his papers, which found an appropriate 
 place in the Philosophical Transactions \ 
 have given him a title to high rank among 
 the natural philosophers of the eighteenth 
 century. To the consideration of this side 
 of his achievement I shall now turn. 
 
II 
 
 CONTRIBUTIONS TO PHYSICS 
 
 IT was in the realm of Physics that 
 the originality and brilliance of John 
 Michell's mind found their widest scope. 
 A living writer has recently said : "In 
 the entire century which elapsed between 
 the death of Newton and the scientific 
 activity of Green, the only natural philo- 
 sopher of distinction who lived and taught 
 at Cambridge was Michell ; and for some 
 reason which, at this distance of time, it 
 is difficult to understand fully, Michell's 
 researches seem to have attracted little or 
 no attention among his collegiate con- 
 temporaries and successors, who silently 
 acquiesced when his discoveries were 
 attributed to others, and allowed his 
 name to perish entirely from Cambridge 
 tradition 1 ." There can at least be no 
 
 1 A History of the Theories of Aether and Electricity ', 
 by Professor E. T. Whittaker, F.R.S., 1910, p. 167. 
 
 7 2 
 
doubt that in his lifetime Michell en- 
 joyed the esteem and respect of the most 
 eminent men of science in his day. 
 His distinction as an investigator was 
 promptly recognised, as we have seen, 
 by his early election into the Royal 
 Society, when Henry Cavendish and 
 other men of note became his friends and 
 correspondents. But it was not until after 
 he left Cambridge that his eminence in 
 natural philosophy was displayed in the 
 successive papers which he communicated 
 to the Philosophical Transactions. 
 
 The consideration of his researches in 
 physical science may be grouped under 
 the heads of (A) Magnetism, (B) Vision, 
 Light, etc., (C) The Density of the Earth. 
 A separate section will be devoted to his 
 investigations in Astronomy. 
 
 A. Magnetism 
 
 In Michell's first published essay in 
 science the little volume on Artificial 
 Magnets two of his prominent charac- 
 
 73 
 
tcristics were conspicuously shown, 
 originality and modesty. Though from 
 the title of the book it might be supposed 
 to be merely a new method of producing 
 artificial magnets, it yet contained some 
 fresh researches in magnetism including 
 the discovery of the law of attraction 
 which is " the basis of the mathematical 
 theory of Magnetism 1 /' The author 
 believed his method of making artificial 
 magnets to be a contrivance of his own, 
 but he admitted that it might prove to be 
 the same as that of his eminent contem- 
 porary Dr Gowin Knight. But of much 
 more importance than the originality of 
 
 1 Whittaker, History of Theories of Aether and 
 Electricity^ p. 55. The full title-page of MichelFs 
 work is as follows: u A Treatise of Artificial Magr 
 nets; in which is shewn an easy and expeditious 
 Method of making them, superior to the best natural 
 ones, by J. Michell, B. A. Fellow of Queens' College, 
 Cambridge. Printed by J. Bentham, Printer to the 
 University and sold by W. and J. Mount and 
 T. Page on Tower Hill&c. MDCCL. (Price i/-)." 
 The copy of the volume in the Library of the Royal 
 Society has a MS. note at the foot of the title-page : 
 "Presented March 22, 1750." 
 
 74 
 
his invention was the light which he was 
 able to throw on the laws of magnetism. 
 Thus he found that according to his 
 observations " the magnetical attraction 
 and repulsion are exactly equal to each 
 other." He made and announced the 
 discovery that " the attraction and re- 
 pulsion of magnets decreases as the squares 
 of the distances from the respective poles 
 increase." Yet he modestly remarks 
 that, although his own experiments made 
 the conclusion very probable, "I do not 
 pretend to lay it down as certain, not 
 having made experiments enough yet to 
 determine it with sufficient exactness 1 ." 
 It will be remembered that his contri- 
 bution to magnetism was one of the 
 grounds set forth in the certificate for 
 his election into the Royal Society, and 
 that one of his sponsors was Dr Gowin 
 Knight, the most noted authority of the 
 day on this branch of science. 
 
 1 Treatise of Artificial Magnet^ p. 19. 
 
 75 
 

 
 B. Vision, Light, and Colours 
 
 Interesting proof of the range of 
 Michell's studies in natural philosophy 
 and of the singularly large-minded gene- 
 rosity with which he freely communi- 
 cated to other fellow-workers the results 
 of his own unpublished researches is 
 furnished by the record of his association 
 with Joseph Priestley. That illustrious 
 philosopher became minister of Mill Hill 
 Chapel, Leeds, in 1767, the same year 
 that saw John Michell settled in the 
 rectory of Thornhill. He had already 
 made known his growing heterodoxy, 
 but he had also shown such striking 
 powers in scientific discussion, particu- 
 larly in regard to electricity, that the 
 Royal Society had already in 1766 elected 
 him one of its body. Leeds and Thorn- 
 hill being only a few miles apart, it was 
 natural that the two men of science 
 should become acquainted with each 
 other. In these days it said much for the 
 76 
 
broad-mindedness of the Rector of Thorn- 
 hill that he entered into the friendliest 
 relations with the Unitarian dissenter. 
 He could hardly fail to be interested in 
 the publication of Priestley's volume on 
 The History and Present State of Electricity 
 which made its appearance in this same 
 year 1767. During the lapse of a few 
 years much friendly personal intercourse, 
 as well as correspondence, arose between 
 the two men. Priestley had then begun 
 to collect material for another work on 
 physical science which was published in 
 1 772 *. During the five years over which 
 the writing of this treatise extended, he 
 frequently consulted the Rector on the 
 various questions which he had to discuss, 
 and he fully acknowledged the value of 
 the assistance which was always willingly 
 forthcoming from that source. He has 
 stated that "in writing the History of the 
 
 1 The title of this work is History and Present 
 State of Discoveries relating to Vision, Light and 
 Colour j, 2 vols. 4 to, 1772. 
 
 77 
 
Discoveries relating to Vision* I was much 
 assisted by Mr Michell, the discoverer of 
 the method of making artificial magnets. 
 Living at Thornhill not very far from 
 Leeds, I frequently visited him, and was 
 very happy in his society 1 ." 
 
 In the two quarto volumes to which 
 Priestley refers in this quotation, he ac- 
 knowledges in detail his indebtedness to 
 Michell. From his statements and his 
 quotations from the Rector's letters we 
 learn what were MichelFs views on a 
 number of physical questions on which 
 he does not appear ever to have himself 
 published anything. Thus in reference 
 to the seat of vision, Priestley remarks : 
 " I shall beg leave to present to my 
 readers some other arguments which 
 escaped the notice of previous observers, 
 but which were suggested to me by my 
 friend Mr Michell 2 ." Later in the same 
 
 1 Life cmd Correspondence of Joseph Priestley^ by 
 J. T. Rutt, 1831, vol. I, p. 78. 
 
 Op. at. vol. i, p. 198. Michell as a staunch 
 
 78 
 
volume he states : " My objections to 
 Newton's manner of accounting for the 
 colours of thin plates are of long standing, 
 but the hint of accounting for them in the 
 manner that I have attempted to do [by 
 the doctrine of attractions and repulsions] 
 was first suggested to me by Mr Michell, 
 agreeably to whose conjectures relating 
 to this subject, I have given the preceding 
 account of the probable cause of these 
 appearances 1 ." 
 
 Priestley likewise refers to MichelFs 
 skill in devising apparatus for the purpose 
 of illustrating or solving physical pro- 
 blems. Thus with regard to another 
 phenomenon of light he states : " Mr 
 Michell some years ago endeavoured to 
 ascertain the momentum of light in a 
 much more accurate manner than those 
 in which M. Homberg and M. Mairan 
 had attempted it ; and though his appa- 
 
 fol lower of Newton believed in the corpuscular 
 theory of light. 
 1 Vol. I, p. 311. 
 
 79 
 
ratus was disordered by the experiment, 
 and on other accounts, he did not pursue 
 it so far as he had intended, it was not 
 wholly without success ; and the con- 
 clusions that may be drawn from it are 
 curious and important 1 ." 
 
 After describing the apparatus which 
 had been employed, Priestley proceeds 
 to show that the conclusions which its 
 contriver was disposed to draw from his 
 observations, as far as they had gone, 
 pointed to the " mutual penetrability of 
 matter." He states that the ingenious 
 hypothesis of Boscovich on this subject, 
 " or at least one that is the same in every- 
 thing essential, occurred also to my friend 
 Mr Michell, in a very early period of 
 his life, without his having had any 
 communication with M. Boscovich, or 
 even knowing that there was such a 
 person. These two philosophers had 
 even hit upon the same instances, to 
 confirm and illustrate their hypotheses, 
 
 1 Op. clt. p. 387. 
 80 
 
especially those relating to contact, light 
 and colours. 
 
 " This scheme of the immateriality of 
 matter, as it may be called, or rather, the 
 mutual penetration of matter, first occurred 
 to Mr Michell on reading Baxter On the 
 Immateriality of tlie Soul. He found that 
 this author's idea of matter was, that it 
 consisted, as it were, of bricks, cemented 
 together by aq immaterial mortar. These 
 bricks, if he would be consistent to his 
 own reasoning, were again composed of 
 less bricks, cemented, likewise, by an 
 immaterial mortar and so on ad infantum. 
 This putting Mr Michell upon the con- 
 sideration of the several appearances of 
 nature, he began to perceive that the 
 bricks were so covered with this im- 
 material mortar, that if they had any 
 existence at all, it could not possibly be 
 perceived, every effect being produced, at 
 least in nine instances in ten certainly, 
 and probably in the tenth also, by this im- 
 material, spiritual and penetrable mortar. 
 c. 81 
 

 Instead, therefore, of placing the world 
 upon the giant, the giant upon the 
 tortoise, and the tortoise upon he could 
 not tell what, he placed the world at 
 once upon itself; and finding it still 
 necessary, in order to solve the appear- 
 ances of nature, to admit of extended 
 and penetrable immaterial substance, if 
 he maintained the impenetrability of 
 matter ; and observing farther, that all 
 we perceive by contact, etc. is this pene- 
 trable immaterial substance, and not the 
 impenetrable one, he began to think he 
 might as well admit of penetrable material, 
 as well as penetrable immaterial substance, 
 especially as we know nothing more of 
 the nature of substance, than that it 
 is something which supports properties, 
 which properties may be whatever we 
 please, provided they be not inconsistent 
 with each other, that is, do not imply 
 the absence of each other. This by no 
 means seemed to be the case in supposing 
 two substances to be in the same place at 
 82 
 
the same time, without excluding each 
 other ; the objection to which is only 
 derived from the resistance we meet with 
 to the touch, and is a prejudice that has 
 taken its rise from that circumstance, and 
 is not unlike the prejudice against the 
 Antipodes, derived from the constant ex- 
 perience of bodies falling, as we account 
 it, downwards 1 ." 
 
 In connection with other problems 
 in light and vision Priestley refers to 
 information supplied to him by Michell 
 and quotes from some of the philosopher's 
 published astronomical papers where these 
 problems are considered. 
 
 1 Op. at. pp. 392-3. As Professor Whittaker 
 has pointed out, Faraday's suggestion that "an 
 ultimate atom may be nothing else than a field of 
 force electric, magnetic and gravitational sur- 
 rounding a point-centre, is substantially the view of 
 Michell and Boscovich." History of the Theories of 
 Aether and Electricity (1910), p. 217. 
 
C, The Density of the Earth 
 
 The most ingenious and most im- 
 portant piece of apparatus devised by 
 John Michell at his Yorkshire home was 
 his bold and original invention of the 
 Torsion-balance with which he proposed 
 to determine the mean density of the 
 Earth. It was probably his last feat in 
 mechanical contrivance, at least he did 
 not live to put it into use. After his 
 death the apparatus passed into the hands 
 of Henry Cavendish who, making some 
 modifications and improvements in it, 
 carried out MichelFs purpose with 
 brilliant success, in what has since been 
 known as the " Cavendish experiment. 1 * 
 In communicating his account of the 
 experiment to the Royal Society 1 , Caven- 
 dish, who seemed so indifferent to the 
 recognition of his own scientific work, 
 took care to bear his testimony to the 
 
 1 Phil. Trans, vol. 88 (1798), p. 469. The paper 
 was read to the Society on 2ist June 1798. 
 
originality of his deceased friend. "Many 
 years ago," so he wrote, " the Rev. John 
 M ichell of this Society contrived a method 
 of determining the density of the earth, 
 by rendering sensible the attraction of 
 small quantities of matter ; but as he was 
 engaged in other pursuits, he did not 
 complete the apparatus till a short time 
 before his death, and did not live to make 
 any experiments with it. After his death 
 the apparatus came to the Rev. Francis 
 John Hyde Wollaston, Jacksonian Pro- 
 fessor at Cambridge, who not having 
 conveniences for making experiments 
 with it, in the manner he could wish, 
 was so good as to give it to me." 
 
 " The apparatus is very simple : it 
 consists of a wooden arm, 6 feet long, so 
 as to unite great strength with little 
 weight. This arm is suspended in an 
 horizontal position, by a slender wire, 
 40 inches long, and to each extremity is 
 hung a leaden ball, about 2 inches in 
 diameter, and the whole is enclosed in 
 
a little wooden case to defend it from 
 the wind. 
 
 "As no more force is required to make 
 this arm turn round on its centre than 
 what is necessary to twist the suspending 
 wire, it is plain that if the wire is suffi- 
 ciently slender, the most minute force, 
 such as the attraction of a leaden weight 
 a few inches in diameter, will be sufficient 
 to draw the arm sensibly aside. The 
 weights which Mr Michell intended to 
 use were 8 inches in diameter. One of 
 these was to be placed on one side of the 
 case opposite to one of the balls, and as 
 near it as could conveniently be done, and 
 the other on the other side, opposite to 
 the other ball, so that the attraction of 
 both these weights would conspire in 
 drawing the arm aside ; and, when its 
 position, as affected by these weights, 
 was ascertained, the weights were to be 
 removed to the other side of the case, so 
 as to draw the arm the contrary way, and 
 the position of the arm was to be again 
 86 
 
determined ; and consequently, half the 
 difference of these positions would shew 
 how much the arm was drawn aside by 
 the attraction of the weights. 
 
 " In order to determine from hence 
 the density of the Earth, it is necessary 
 to ascertain what force is required to draw 
 the arm aside through a given space. 
 This Mr Michell intended to do, by 
 putting the arm'in motion, and observing 
 the time of its vibrations, from which it 
 may easily be computed 1 ." 
 
 " Mr Michell had prepared two wooden 
 stands on which the leaden weights were 
 to be supported, and pushed forwards, 
 till they came almost in contact with 
 the case ; but he seems to have intended 
 to move them by the hand. 
 
 "As the force with which the balls 
 
 1 " Mr Coulomb has, in a variety of cases, used 
 a contrivance of this kind for try ing small attractions; 
 but Mr Michell informed me of his intention of 
 making this experiment, and of the method he in- 
 tended to use, before the publication of any of 
 Mr Coulomb's experiments." [Note by Cavendish .] 
 
are attracted by these weights is exces- 
 sively minute, not more than 
 
 their weight, it is plain that a very 
 minute disturbing force will be sufficient 
 to destroy the success of the experiment ; 
 and from the following experiments it 
 will appear, that the disturbing force 
 most difficult to guard against is that 
 arising from the variations of heat and 
 cold ; for, if one side of the case is 
 warmer than the other, the air in con- 
 tact with it will be rarefied, and, in 
 consequence, will ascend, while that on 
 the other side will descend, and produce 
 a current which will draw the arm 
 sensibly aside. 
 
 " As I was convinced of the necessity 
 of guarding against this source of error, 
 I resolved to place the apparatus in a room 
 which should remain constantly shut, and 
 to observe the motion of the arm from 
 without, by means of a telescope ; and 
 to suspend the leaden weights in such 
 a manner, that I could move them with- 
 88 
 
out entering the room. This difference 
 in the manner of observing, rendered it 
 necessary to make some alteration in 
 Mr Michell's apparatus ; and as there 
 were some parts of it which I thought 
 not so convenient as could be wished, 
 I chose to make the greatest part of it 
 afresh." 
 
 The " Cavendish experiment r has 
 become famous in the annals of physical 
 science. One of the most appreciative 
 accounts of it and of Michell's share in 
 preparing for it was penned by the dis- 
 tinguished Professor of Natural Philo- 
 sophy in the University of Edinburgh, 
 James David Forbes, more than half a 
 century after both Michelland Cavendish 
 had been laid in the grave. The con- 
 cluding sentences of his narrative may be 
 quoted here : " Cavendish conducted the 
 experiment with his usual patience, judg- 
 ment and success ; he found the joint 
 attraction of the small balls and large 
 spheres to be about ^ of a grain, their 
 
 89 
 
centres being 8-85 inches apart, and he 
 thence computed the density of the 
 Earth to be 5-48 times that of water. 
 Cavendish's paper is, as usual, a model of 
 precision, lucidity and conciseness. It 
 would be difficult to mention in the 
 whole range of physics a more beautiful 
 and more important experiment 1 ." 
 
 Since Cavendish improved Michell's 
 apparatus and first put it to the use for 
 which its designer constructed it, the 
 experiment has been repeated by several 
 observers with an approximately similar 
 result 2 . The most recent repetition is 
 that of Mr C. V. Boys. By an ingenious 
 reconstruction of apparatus and availing 
 himself of the great sensibility obtained 
 by the use of quartz-fibres instead of 
 metal wires this accomplished physicist 
 
 1 Professor Forbes* description is contained in 
 the Sixth Dissertation of the Eighth Edition of the 
 Encyclopaedia Bntannlca^ p. 834. 
 
 2 See Reich, Compt. rendus^ 1837, p. 697 ; Baily, 
 Mem. Astron. Soc. vol. XIV; Phil. Mag. xxi (1842), 
 p. Ill ; Cornu, Compt. rend. vol. 86, pp. 571, 699, 
 1OOI. 
 
 9 
 
has computed the mean density of the 
 Earth to be 
 
 III 
 CONTRIBUTIONS TO ASTRONOMY 
 
 THE studies pursued by John Michell in 
 this branch of science were marked by 
 his characteristic originality and insight. 
 Not only was he an actual observer of 
 the heavens, working with a reflecting 
 telescope of his own construction, but in 
 his theoretical discussion of stellar phe- 
 nomena he introduced the mathematical 
 computation of probabilities, and showed 
 sometimes a remarkable prescience that 
 seems to anticipate the discoveries of 
 more recent times. Reference has already 
 been made to the family tradition that 
 Michell gave William Herschel his first 
 lessons in Astronomy and taught him the 
 art of making reflectors. Before entering 
 
 1 Boys, "On the Newtonian Constant of Gravi- 
 tation,*^//. Tram. vol. 1 86(1 896) ; seealsoPrw. Roy. 
 Soc. vol. 46, p. 253 ; Proc. Roy. Imtit. vol. xiv (i 894). 
 
 9' 
 
on the consideration of Michell's own 
 astronomical work it maybe convenient if 
 we take note of what were the actual per- 
 sonal relations of these two astronomers. 
 It is now clearly established that they 
 started quite independently of each other 
 in the actual construction and employ- 
 ment of the reflecting telescope. We do 
 not know when and under what con- 
 ditions the Rector of Thornhill began to 
 construct the large instrument which 
 ultimately became the property of Her- 
 schel, but it would appear that he had 
 made considerable progress, if he had not 
 completed it before 1781. Herschel did 
 not begin to study astronomy until 
 1773 when he was still actively engaged 
 in the multifarious duties of his musical 
 profession at Bath. In the following 
 year he began to grind specula 1 . After 
 six years, during which he worked la- 
 boriously with his telescope, he was able 
 
 1 The Scientific Papers of Sir William HerscM, 
 vol. I, pp. xxxi-xxxii. 
 
 92 
 
in the summer of 1780 to send to the 
 Royal Society two papers in which the 
 results of his first researches were given 1 . 
 These papers revealed to \ne world the 
 advent of a new astronomer of unusual 
 promise. They would probably be kno\vn 
 and appreciated by Michell, for they 
 appeared in the Philosophical "Transactions. 
 But, as already stated (p. 18), they were 
 more pointedly brought to his notice by 
 his friend Dr Watson, who had interested 
 himself at Bath in the work of the pre- 
 cocious astronomical musician. Herschel 
 took advantage of the opening provided by 
 Michell's letter to him of 2 ist January 
 1781. To two of his letters Michell sent 
 him a long reply (i2th April) dealing 
 with the construction of mirrors and the 
 relative merits of different types for large 
 and small apertures. Only a month before 
 this letter was written Herschel had made 
 his great discovery of Uranus, and had 
 thus leaped into a foremost place among 
 
 1 Phil. Trans, vols. 70 and 71. 
 
 93 
 
the astronomers of the world. The cor- 
 respondence between him and the Rector 
 of Thornhill does not appear to have been 
 maintained ; but as Herschel was elected 
 a Fellow of the P.oyal Society on 6th 
 December 1781, the two men of science 
 \vould now have opportunities of personal 
 intercourse at the meetings of the Society 
 and the convivial gatherings of the Royal 
 Society Club. Herschel in subsequent 
 years took occasion, in a paper read before 
 the Royal Society, to refer appreciatively 
 to the work done at Thornhill. "Mr 
 Michell," he said, " has also considered 
 the stars as gathered together into groups 
 (Phil. Trans, vol. 57, 1767, p. 249) which 
 agrees with the subdivision of our great 
 system here pointed out. He founds an 
 elegant proof of this on the computation 
 of probabilities, and mentions the Pleiades, 
 the Praesepe Cancri, and the nebula (or 
 cluster of stars) in the hilt of Perseus's 
 sword as instances 1 ." 
 
 1 Phil. Trans. 75 (1785). 
 
 94 
 
The only record which I have been 
 able to recover of an actual meeting of 
 the two astronomers was one made by 
 Herschel during a tour in the year 1792 
 when he passed through Thornhill and 
 called at the rectory. But the Rector, 
 now near the close of his life, was dis- 
 abled and frail. Herschel has noted : 
 "We saw Mr Michell's telescope; it is 
 on an equatorial stand, being without 
 cover behind. I put my hand into the 
 opening and felt the face of the object 
 speculum so wet as to moisten my fin- 
 gers. Mr Michell was very indifferent 
 in health." 
 
 When Herschel, in the course of a 
 holiday trip with his wife next year, 
 spent a couple of hours at the place, 
 Michell had already passed away, and 
 the instruments that had gradually been 
 accumulated at the rectory were about 
 to be removed. He took another look at 
 the collection and made a note that he 
 had "bought Mr MichelTs great tele- 
 
 95 
 
scope and paid Mr Turton 30 pounds 1 .'* 
 It is interesting to know that the instru- 
 ment was put into good order and was 
 used in his subsequent researches by the 
 great astronomer into whose hands it had 
 come. 
 
 We may now pass on to consider 
 Michell's genius for astronomy as dis- 
 played in the papers which he communi- 
 cated to the Royal Society and which 
 duly appeared in the Philosophical Trans- 
 actions. I am glad to be able to present 
 the following estimate of these papers, 
 which at my request has been prepared 
 for this Memoir by my friend Sir Joseph 
 Larmor. 
 
 " In designing his apparatus to measure 
 the gravitational attraction of a globe of 
 lead, and thence to deduce the mean 
 density of the Earth, Michell was the 
 pioneer in the standard method of deter- 
 mining very small forces by taking advan- 
 tage of the torsion produced by them 
 
 1 Herscbirs Scientific Papers, vol. I, p. Ix. 
 
 9 6 
 
in a wire. It was shortly afterwards, as 
 Cavendish remarks, that Coulomb ap- 
 plied the same principle, in a classical 
 series of experiments, to the exact deter- 
 mination of electric and magnetic attrac- 
 tions : and, in various more convenient 
 forms, it is now one of the main resources 
 of delicate physical measurement. But 
 Michell's (and. Cavendish's) mastery of 
 it, and his just anticipation of its power, 
 went far beyond his age ; he designed 
 and constructed appliances with con- 
 fidence, for a precise estimation of forces 
 so minute that they could hardly even be 
 detected in any other way : even nowa- 
 days his application of the principle to 
 gravitation demands the resources of a 
 master. 
 
 "It is to be expected that a man who 
 could confidently engage in preparations 
 to weigh a ball of lead against one of the 
 celestial bodies would be capable of deep 
 views on other astronomical questions. 
 An examination of his Memoir of 1767 
 c. 97 
 
confirms this surmise *. As regards general 
 astronomical speculation on stellar sys- 
 tems and their nature, it gives him a place 
 alongside Huygens, Wright and Kant 2 . 
 Further, in more definite fields, it credits 
 him with initiation of the applicati Dn of 
 mathematical methods, resting on proba- 
 bility and statistics, to the celestial sys- 
 tems. The quantity of material which 
 had then been accumulated was far too 
 small for wide statistical inferences of 
 much certainty ; yet Michell amply 
 demonstrated, for the first time 3 , the 
 
 1 The title of this paper is as follows : " An 
 inquiry into the probable Parallax and Magnitude 
 of the Fixed Stars from the quantity of Light which 
 they afford us, and the particular circumstances of 
 their situation." Phil. Trans, vol. 57 (l 767), p. 234. 
 Herschel's reference to this paper has been referred 
 to ante, p. 95. Later references will be found in 
 Todhunter's History of the Mathematical Theory of 
 Probability (1865), where it is stated that the paper 
 had "attracted considerable attention." MichelFs 
 method of enquiry is there quoted and his results are 
 given (pp. 332, 393, 491). 
 
 8 See R. Grant, History of Physical Astronomy, 
 
 PP- 543, 558, 559- 
 
 3 Grant, op. cit. p. 547. 
 
 9 8 
 
most fundamental fact of stellar cosmo- 
 gony, the existence of physically-con- 
 nected stellar groups. In the case of the 
 conspicuous pairs of adjacent stairs (the 
 so-called double stars) he anticipated that 
 orbital revolution round each other, 
 owing to their mutual gravitation, would 
 in time be detected, a prediction after- 
 wards brilliantly realised on a grand scale 
 by Sir William Herschel. He even 
 pointed out that knowledge of the period 
 of their orbital revolution, combined 
 with their distance from the solar sys- 
 tem, would provide means of determining 
 the mass of such a stellar pair in com- 
 parison with the mass of the Sun 1 , a 
 problem which is being worked out 
 into exact knowledge by aid of refined 
 determinations of parallax in our own 
 time. 
 
 " These considerations occur in the 
 course of discussion of a plan for esti- 
 mating the distances of the stars by com- 
 
 1 Phil. Tram. 1784, p. 36, et $eq. 
 
 99 
 
paring their brightness with that of the 
 Sun, on the assumption that they give 
 out an amount of light not greatly differ- 
 ent from his. This method had, it seems 1 , 
 been first suggested by James Gregory ; 
 it was applied roughly by Huygens to 
 Sirius ; and it attracted the attention of 
 Lambert and later of Olbers, as well as 
 that of Michell. In MichelFs argument 
 the planet Saturn, whose size and distance 
 are known from the Newtonian theory, 
 and whose brightness relative to the Sun 
 could thus be estimated, was used as an 
 intermediary ; for it would be impossible 
 to compare directly the dazzling bright- 
 ness of the Sun with the amount of light 
 received from a star. These astronomers 
 all agree in assigning a parallax less than 
 half a second of arc to the brightest stars; 
 and this is in fact near the values that are 
 now known for the very few nearest stars, 
 which are thus at a distance from our 
 system of about a million times that of 
 
 1 Grant, op. clt. p. 547. 
 IOO 
 
the Earth from the Sun, while most stars 
 are very many times more remote. 
 
 " Michell was the first 1 to propound,, 
 in the same Memoir, just views as to the 
 simple proportionality between the faint- 
 ness of the stars just visible in a telescope 
 and the area of its aperture, no other 
 circumstance being essentially concerned. 
 He initiated the application of this prin- 
 ciple to the estimation of the distribution 
 of the stars at different distances in the 
 depths of space, a task afterwards carried 
 out so tenaciously and brilliantly in the 
 'star-gauging' of Sir William Herschel. 
 He concluded from a discussion of proba- 
 bilities that the bright stars were more 
 numerous around our system than a uni- 
 form distribution in the celestial spaces 
 would permit ; and he inferred that most 
 of the bright stars that did not obviously 
 belong to star-groups were our nearer 
 neighbours, and constituted a stellar 
 system of which our own solar system is 
 
 1 Grant, *p. at. p. 543. 
 
 IOI 
 
a part ; while the fainter stars in the 
 depths of space may be grouped in other 
 stellar systems. Thus he thought the 
 nebulae were separated universes of stars, 
 so far away as to defy resolution into 
 their components. Modern astronomical 
 theories are now moving, of course far 
 more definitely, along similar lines, forti- 
 fied by the immense masses of facts 
 relating to distances, motions and con- 
 stitutions of the stars and nebulae, which 
 are provided by the photographic plate 
 and the spectroscope in conjunction with 
 large telescopes. 
 
 " In Michell's day the available data 
 were utterly inadequate to guide to safe 
 statistical conclusions on matters of such 
 delicate inference. But the mathematical 
 modes of reasoning in his Memoir of 1767 
 are still of much interest in the light of 
 modern knowledge, especially as they are 
 illustrated by a discussion of the group of 
 the Pleiades, as it is presented to the naked 
 eye and also in telescopes of various aper- 
 102 
 
tures. It may be claimed that these modes 
 of reasoning give Michell a place as the 
 early pioneer in the great modern problem 
 of the configuration and structure of the 
 universe, which first rose to prominence 
 twenty years afterwards, by the labours 
 of Sir William Herschel, founded on 
 similar views. 
 
 "In regard, to optics, Michell was a 
 thoroughgoing Newtonian, as was natural 
 in his time. Light for him consisted of 
 corpuscles projected from the luminous 
 body, rather than waves propagated 
 through an aether. He even thought 
 that, like everything material, they must 
 be subject to gravitation ; and he de- 
 veloped a speculation that the velocities 
 of the corpuscles shot out from one of the 
 larger stars must be sensibly diminished 
 by the backward pull of its attraction, 
 and thus be more deviated by a glass prism, 
 a supposition which he proposed to test. 
 At the end of his Memoir of 1767 (p. 261) 
 he even suggests that the c twinkling of 
 
 103 
 
the fixed stars' is due to the small number 
 of luminous corpuscles received by the 
 eye which might be only a few per second. 
 These corpuscular optical speculations 
 now carry special interest as a curiously 
 definite foreshadowing of the work on 
 electric radio-activity, in which Thomson , 
 Rutherford and others have actually con- 
 trolled the velocities of the electric cor- 
 puscles by the agency of field of force, and 
 have directly counted the numbers of 
 
 r 
 
 them that are shot out from active matter. 
 " In his wide outlook over the field of 
 nature, in the extent of knowledge that 
 was linked together in his active interests, 
 Michell was a true disciple of the British 
 school of physical science, the con- 
 temporary members of which were largely 
 his personal friends. They were falling 
 behind in mathematical analysis, owing 
 to too conservative partiality for the 
 geometrical methods of their master 
 Newton. While the great analysts of the 
 continent were closely engaged in the 
 104 
 
expansion of the infinitesimal calculus and 
 its improvement by application to the 
 verification and prediction of the motions 
 of the solar system, the mathematicians 
 of Britain had time for wider, though less 
 intricate contemplation of the correlations 
 of natural phenomena, not seldom leading 
 into general views which subsequent times 
 were to develop with fuller knowledge." 
 
 105 
 
INDEX 
 
 Astronomy, MichelFs contributions to, 91105 
 
 Balderton, 67 
 
 Baxter, on the immateriality of the Soul, 81 
 
 Birch, Dr T., 1 1 
 
 Blagden, Sir Charles, 46, 49, 55, 60, 63 
 
 Boscovich, R. G., 80, 83 
 
 Boys, C. V., 90 
 
 Bridport, 60 
 
 Brotherton, 66 
 
 Castle Howard, 63 
 
 Cavendish, Hon. Henry, 3, 12, 20, 45, 47, 59, 
 
 84-90 
 
 Chalk, 60, 63, 64, 66 
 Coulomb, C. A. de, 87, 97 
 Dorchester, 60 
 Dunstable, 63 
 
 Earth, determination of mean density of, 84 
 Earthquakes, Michell on, 25-39 
 Exeter, 62 
 Faraday, M., 83 
 Farey, John, 65, 66 
 Fitton, Dr, 70 
 Fitzpatrick, Rev. T. C., 4 
 Forbes, James David, 89 
 Foston, 55, 56 
 Gault, 66 
 
 Geology, Michell's contributions to, 24-58 
 Grantham, 54, 67 
 Greetham Common, 50 
 
 1 06 
 
Gunnerby Hill, 55, 56, 63 
 
 Hadley, Prof. J., 1 1 
 
 Haldon Hill, 62 
 
 Herschel, Sir William, 14, 19, 91-96, 101, 103 
 
 Homberg, M., 79 
 
 Humber, 63 
 
 Knight, Dr Gowin, 1 1, 74 
 
 Larmor, Sir Joseph, 96 
 
 Leeds, 76 
 
 Lias, 53, 61, 62, 66, 67 
 
 Light, Michell's conception of, 79, 103 
 
 Lyell, Sir Charles, 69 
 
 Lyme, 61 
 
 Magnetism, Michell on, 73 
 
 Mairan, M., 79 
 
 Maty, Dr i\l., 1 1 
 
 Michell, John, earliest account of, 3 ; at Queens' 
 College, Cambridge, 4-6 ; Woodwardian Pro- 
 fessor of Geology, 6 ; his personal appearance, 7 ; 
 Fellow of Queens', ** ; his treatise on Magnets, 
 8, 73; his Essay on Earthquakes, 9, 25; elected 
 into the Royal Society, 1 1, 73 ; Rector ot Comp- 
 ton, 12; his Marriage, 12 ; Rector of Havant, 13; 
 his daughter, 13, 14; family traditions, 13; Rec- 
 tor of Thornhill, 13; his connection with London, 
 2O ; his early interest in geology, 21; his death 
 and epitaph at Thornhill, 23 
 
 His contributions to Geology, 24-58 ; on the 
 causes and phenomena of Earthquakes, 25 ; on 
 the structure of the stratified part of the Earth's 
 crust, 39; his contributions to Physics, 72-90; 
 on Magnetism, 73 ; on V ision, Light, etc., 76 ; 
 on the immateriality of Matter, 81 ; his Torsion- 
 balance for determining the mean density of the 
 Earth, 84; his contributions to Astronomy, 91- 
 105 
 
 107 
 
Minehead, 62 
 
 Physics, Michell's contributions to, 72-90 
 
 Priestley, Joseph, 3, 76, 77, 78-83 
 
 Queens' College, Cambridge, 3, 14 
 
 Roch Abbey, 66 
 
 Royal Society, 2, 7, 9, 10, 20, 25, 73, 76, 94 
 
 Royal Society Club, 2, 2O, 58, 94 
 
 Scarborough, 68 
 
 Selenite, 53 
 
 Sherewood Forest, 66 
 
 Sid mouth, 6 1 
 
 Sills or Intrusive Sheets, 37 
 
 Smeaton, John, 65 
 
 Smith, William, 68 
 
 Stars, twinkling of, 103 
 
 Strachey, John, 39 
 
 Thornhill Rectory, 13, 22, 23, 58, 76, 95 
 
 Thorpe, Sir T. Edward, 46 
 
 Torsion-balance of Michell, 84, 89, 96 
 
 Tuxford, 66 
 
 Vapour, subterranean, 29, 36 
 
 Vision, Light, etc., Michell on, 76-83 
 
 Watchett, 62 
 
 Wernerian geognosy, 27 
 
 Whin Sill of North England, 38 
 
 Whittakcr, Prof. E. T., 72, 83 
 
 Wilson, George, biographer of Cavendish, 3, 47 
 
 Wollaston, F. J. Hyde, 85 
 
 Woodward, John, 6, 40 
 
 Wray, Dr D., 1 1 
 
 " Yellow Limestone/' (Jurassic) 48, 60, (Permian) 
 
 56, 63, 64 
 Zittel, K. A. von, 70 
 
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