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MICHELL, JOHN (1724–1793), astronomer, was born apparently in 1724. He was described as of Nottinghamshire when he was admitted to Queens' College, Cambridge, on 17 June 1742. He was elected a bible-clerk there on 23 Jan. 1747, and graduated as fourth wrangler in 1748. He was elected to a fellowship in 1749, and proceeded M.A. in 1752, and B.D. in 1761. He served the college offices of lecturer in Hebrew (1751-2, 1759-60, 1762), in arithmetic (1751-2), in geometry (1753-4, 1763), in Greek (1755-6, 1759-60), and was theological censor (1753-5), senior bursar (1766-60), and philosophical censor (1760). From 20 March 1760 till June 1763 he was rector of St. Botolph's, Cambridge, and he resigned his fellowship on 8 April 1764. His membership of the Royal Society dated from 12 June 1760, but his name does not appear in the lists until 1762, in which year he was appointed Woodwardian professor of geology at Cambridge. In 1767 he became rector of Thornhill in Yorkshire, where he resided until his death. His leisure and fortune were devoted to the promotion of science; but he also cultivated music, and was no mean violinist. Although the statement involves some chronological difficulty, there seems no doubt that William Herschel [q.v.] often performed on the violin at his entertainments, which were attended by Priestley, the Hon. Henry Cavendish [q.v.], and other distinguished persons. From him, too, Herschel received his first lessons in speculum-grinding, and a ten-foot reflector turned out by him eventually came into Herschel's possession.

Michell published at Cambridge in 1750 'A Treatise of Artificial Magnets' (2nd edit. 1751, translated into French, 1752), in which he described the mode of making artificial magnets by 'double touch,' and enunciated the law of variation of magnetic action according to the inverse squares of distances. He communicated to the Royal Society his observations of the comet of January 1760, made at Cambridge with a Hadley's quadrant (Phil. Trans. li. 466), and shortly afterwards 'Conjectures concerning the Cause, and Observations upon the Phenomena of Earthquakes' (ib. p. 566; published separately, London, 1760, 4to), in which he put forward the theory of their origin through the elastic force of subterraneanly generated steam. 'A Recommendation of Hadley's Quadrant for Surveying' followed in 1765 (ib. lv. 70), and a 'Proposal of a Method for Measuring Degrees of Longitude upon Parallels of the Equator' in 1767 (ib. lvi. 119). 'An Enquiry into the Probable Parallax and Magnitude of the Fixed Stars from the Quantity of Light which they afford us,' read 7 and 14 May 1767 (ib. lvii. 234), led him to infer the extreme minuteness of stellar parallax. In the same remarkable paper he argued the overwhelming probability for the physical grouping of the Pleiades, and investigated the possibility of our sun belonging to some similar association. He anticipated, moreover, the detection of the revolutions of double stars, and showed how their relative densities could thence be deduced on the supposition of equal surface-brightness, whatever might be their distances from the earth. He divined, too, the presence of an element in stellar proper motions due to the sun's motion in space, and foresaw that from the amount of this 'secular parallax' might be deduced the distances of the objects affected by it. He finally pointed out the law connecting the visibility of small stars with telescopic aperture, and sought from it guidance as to their distances. Reverting to these problems in 1783 (ib. lxxiv. 35), he reaffirmed the binary nature of pairs of stars, but speculated fruitlessly on a supposed retardation of light through the attraction of its corpuscles by the emitting masses. Michell arrived independently at Boscovich's theory of the constitution of matter (Priestley, History of Optics, i. 392), and inferred that the moon reflects less than one-sixth of the light falling upon it. Several communications from him were embodied in Priestley's 'History of Optics.' Shortly before his death he devised a method and completed an apparatus for weighing the earth by means of the torsion-balance, of which he was the original inventor. The appliances in question passed from the hands of William Hyde Wollaston [q. v.] to those of Cavendish, who successfully carried out in 1798 the experiments planned by their constructor (Phil. Trans. lxxxviii. 469).

Michell died at Thornhill, Yorkshire, on 21 April 1793, in his sixty-ninth year, leaving an only daughter, who died about 1836, aged upwards of eighty. His scientific instruments were presented after his death to Queens' College, Cambridge.

[English Mechanic, xiii. 310 (a communication from Michell's great-grandson); European Mag. xxiii. 400; Whitaker's Hist. of Leeds, p. 326; Knowledge, xv. 108, 206 (J. R. Sutton); Poggendorff's Biog. Lit. Handwörterbuch; Thomson's Hist. of the Roy. Soc.; Grant's Hist. of Astronomy, p. 543; Clerke's Popular Hist. of Astronomy, p. 22, &c.; Cat. Cambridge Graduates; Gent. Mag. 1793, i. 480; information kindly supplied by the Rev. the President of Queens' College, Cambridge.]

A. M. C.