JOHN

See also:

• JOHN MICHELL (1724-1793)

MICHELL (1724-1793)  , English natural philosopher and geologist, was born in 1724, and educated at Queens' College, Cambridge . His name appears fourth in the Tripos list for 1748-1749; and in 1755 he was moderator in that examination . He became M.A. in 1752, and B.D. in 1761 . He was a fellow of his college, and was appointed Woodwardian professor of geology in 1762, and in 1767 rector of Thornhill in Yorkshire, where he died on the 29th of April 1793 . He was elected a fellow of the Royal Society in the same year as Henry Cavendish (176o) . In 1750 he published at Cambridge a work of some eighty pages entitled A Treatise of Artificial Magnets, in which is shown an easy and expeditious method of making them superior to the best natural ones . Besides the description of the method of magnetization which still bears his name, this work contains a variety of accurate magnetic observations, and is distinguished by a lucid exposition of the nature of magnetic induction . He was the original inventor of the torsion balance, which afterwards became so famous in the hands of its second inventor Coulomb . Michell described it in his proposal of a method for obtaining the mean density of the earth . He did not live to put his method into practice; but this was done by Henry Cavendish, who made, by means of Michell's apparatus, the celebrated determination that now goes by the name of Cavendish's experiment (Phil . Trans., 1708) . His most important geological essay was that entitled Conjectures concerning the Cause and Observations upon the Phaenomena of Earthquakes (Phil .

Trans., li . 176o), which showed a remarkable knowledge of the strata in various parts of

England and abroad . Michell's other contributions to science are: " Observations on the Comet of January 176o at Cambridge, Phil . Trans . (176o) ; " A Recommendation of Hadley's Quadrant for Surveying," ibid . (1765) ; " Proposal of a Method for measuring Degrees of Longitude upon Parallels of the Equator," ibid . (1766) ; " An Inquiry into the Probable Parallax and Magnitude of the Fixed Stars," ibid . (1767); " On the Twinkling of the Fixed Stars," ibid . (1767), " On the Means of Discovering the Distance, Magnitude, &c., of the Fixed Stars," ibid . (1784) .