William Cavendish, 3rd Earl of Devonshire, KB, FRS (c. 10 October 1617 – 23 November 1684) was an English nobleman and politician, known as a royalist supporter.He was Lord Lieutenant of Derbyshire from 13 November 1638 to 22 March 1642, was high steward of Ampthill 4 February 1640, and joint-commissioner of array for Leicestershire 12 January 1642.As a prominent royalist he opposed Strafford's attainder, was summoned to a private conference with the queen in October 1641, was with Charles I at York in June 1642, absented himself from his place in the parliament, was impeached with eight other peers of high crimes and misdemeanors, refused to appear at the bar of the House of Lords, was expelled on 20 July 1642, and was ordered to stand committed to the Tower of London.[1] Cavendish returned from the continent in 1645, submitted to the parliament, was pardoned for his former delinquency in 1646, was fined £5,000, and lived in retirement with his mother at Latimer, Buckinghamshire.[1] Cavendish, a virtuoso, was close to John Evelyn, and was one of the original fellows of the Royal Society (20 May 1663), He was a commissioner of trade from 5 March 1668 to 1669, but lived mainly in the country.