Elizabeth his wife. His father, a virtuoso who collected coins and medals, was appointed in 1724 to the vicarage of Harewood, near Leeds, where he remained until his death in 1747. According to the Wilson MSS. preserved in the Leeds Free Library, Knight was educated at the Leeds grammar school. He matriculated at Oxford from Magdalen Hall 5 April 1731, and held a demyship at Magdalen College from 1735 to 1746, proceeding B.A. 20 Oct. 1736, M.A. 22 June 1739, and M.B. 11 Feb. 1741–2. He afterwards settled in London and is said to have practised as a physician. In 1749 he was living in Lincoln's Inn Fields; he removed to a house in Crane Court, Fleet Street, about 1750 (cf. Nichols, Literary Anecdotes, v. 534).
Knight began the magnetical researches which gave him his reputation before 1744. His attention was directed to the subject by witnessing the effects of a flash of lightning upon a ship's compass, and the first results of his labours were presented to the Royal Society in 1744 (Phil. Trans. xliii. 161), when he exhibited some bar magnets of great power, and performed some experiments which proved that he was in possession of an entirely new method of magnetising bars. A paper read by him in 1745 (ib. xliii. 361) discusses the various positions of the poles of magnets. In recognition of the value of these researches the Royal Society in 1745 elected him a fellow, and in 1747 the Copley medal was awarded to him. He found a ready sale for his magnets, and in a further series of papers laid before the society in 1746–7 (ib. xliv. 656–72) dealt more particularly with the theoretical aspects of the question. He withheld a full disclosure of his methods of operating for fear of injuring the sale of his magnets, but he soon found in John Canton, who had also begun the manufacture of artificial magnets, a formidable rival [see Canton, John]. Knight's papers on magnetism were collected and published separately in 1758, with notes and additions by the author. It appears from T. H. Croker's ‘Experimental Magnetism’ (1761), p. 8, that Knight issued proposals in 1760 for publishing by subscription an extensive work on magnetism, in two volumes 4to, but the plan was never carried out. After his death his friend Dr. Fothergill read a paper before the Royal Society (ib. 1776, lxvi. 591), in which Knight's methods of magnetising were more fully disclosed. The paper also contains a description of his ‘magnetic magazine’ or battery, which was for many years in the possession of the Royal Society, but is now missing. In 1779 Benjamin Wilson (ib. lxix. 51) gave an account of Knight's method of making artificial loadstones, which consisted in cementing finely divided metallic iron into a solid mass by the admixture of linseed-oil varnish.
Knight's attention had meanwhile been turned to the mariner's compass, and in a paper read before the society in 1750 (ib. xlvi. 505) he stated that he had examined several compass-needles obtained from the best makers, and found them all defective, being either of feeble directive power or absolutely incorrect as regards direction. These defects were due to the shape of the needles, all of which were possessed of four poles. He recommended a plain rhomboidal bar, and he also suggested improved modes of suspension. Some further improvements already made in Knight's compass by Smeaton were communicated to the society at the same time.
Knight brought his improved compass under the notice of the admiralty, and there is an entry in the official minute book under date 4 April 1751 to the effect that the navy board and the Trinity House authorities had been consulted and various experiments made with the improved compass and bar magnets. Compasses were ordered to be supplied to the Glory, bound for Guinea, the Rainbow going to Newfoundland, the Swan sloop bound to Barbadoes, and to the Vulture and Fortune sloops in the Channel. On 11 Sept. in the same year there is a further order directing the captain of the Fortune to receive Dr. Knight on board at Harwich and to sail northwards according to his directions, for the purpose of experimenting with the new compass. He was accompanied on the voyage by Smeaton (see Annual Register, 1793, Chronicle, p. 256). The results of the trials appear to have been satisfactory (though the captain's reports cannot now be found), and by a minute dated 24 June 1752 the board recommended that Knight should be paid 300l. It appears from this minute that the compass had already been brought to the notice of the board of longitude, probably with a view to its use in determining the longitude by observation of the magnetic variation, but the minutes for this date are missing from the records of the board preserved at the Royal Observatory, Greenwich. There are other entries in the admiralty books relating to the matter, and it appears that Knight's instrument gradually came to be the standard compass for the royal navy. They were also used in the better class of merchant ships. The compasses were made, under Knight's direction, by George Adams the elder [q. v.] of Fleet Street, the mathematical instrument