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MOLYNEUX, SAMUEL (1689–1728), astronomer and politician, born at Chester on 18 July 1689, was the only child of William Molyneux [q. v.] who survived infancy. His father zealously undertook his education on Locke's principles, but died in 1698, leaving him to the care of his uncle, Dr. (afterwards Sir) Thomas Molyneux (1661-1733) [q. v.] He had lost his mother in 1691. Matriculating in his sixteenth year at Trinity College, Dublin, he there formed a friendship with George Berkeley (1685-1753) [q. v.], who dedicated to him in 1707 his 'Miscellanea Mathematical Having graduated B.A. in 1708 and M.A. in 1710, Molyneux devoted two years to the improvement of his estate in co. Armagh, then quitted Ireland, and visited the universities of Oxford and Cambridge, and the seats of some of the English nobility. He met with much civility from the Duke and Duchess of Marlborough at Antwerp during the winter of 1712-13, and was sent by the former in 1714 on a political mission to the court of Hanover, where he witnessed, in the Herrenhausen Garden, the sudden death of the Electress Sophia on 8 June 1714 (Coxe, Life of Marlborough, iii. 360, Wade's edition). He accompanied the royal family to England after the death of Queen Anne, and was made secretary to the Prince of Wales, a post which he retained until the prince became George II.
Molyneux married in 1717 Lady Elizabeth Capel, eldest daughter of Algernon, second earl of Essex. Her fortune was 10,000l., and she inherited 18,000l. with Kew House, on the death, in 1721, of Lady Capel of Tewkesbury, her great-uncle's widow. They had no children. The cultivation of astronomy and optics now engaged Molyneux's efforts. He made the acquaintance of James Bradley [q. v.], and experimented with his assistance, from 1723 to 1725, on the construction of reflecting telescopes of Newtonian design. Their first successful speculum, completed in May 1724, was of twenty-six inches focus. They afterwards turned out one of eight feet, and Molyneux presented to John V, king of Portugal, a reflector made by himself, described and figured in Smith's 'Optics,' ii. 363, plate liii. His communication of the perfected process to Scarlett, the king's optician, and Hearne, a mathematical instrument maker in Whitefriars, was the means of bringing reflecting telescopes into general use.
In 1725 Molyneux resolved to repeat Hooke's attempts to determine stellar annual parallax [see Hooke, Robert], and ordered from Graham a zenith-sector of twenty-four feet radius, with an arc of only 25', showing single seconds by the aid of a vernier. It was mounted on 26 Nov. 1725 in his private observatory at Kew House, and the observations of Draconis made with it by him and Bradley from 3 Dec. 1725 to 29 Dec. 1727 led to the latter's discovery of the aberration of light. Molyneux assisted in setting up Bradley's sector at Wanstead on 19 Aug. 1727, but was unable to prosecute the inquiry much further, owing to the pressure of public business ensuing upon his appointment, on 29 July 1727, as one of the lords of the admiralty. He formed schemes for the improvement of the navy, which his colleagues actively opposed, and these contrarieties perhaps hastened the development of brain disease inherited from his mother. He was seized with a fit in the House of Commons, and, after lingering a few days in stupor, died on 13 April 1728, at the age of thirty-eight. He was a man of winning manners and, obliging temper, and united Irish wit to social accomplishments. His inflexible integrity seemed alone to stand in the way of his high advancement. He was a privy councillor both in England and Ireland, represented the boroughs of Bossiney and St. Mawes, and the city of Exeter in the English parliaments of 1715, 1726, and 1727 respectively, and was returned in 1727 to the parliament of Ireland as member for the university of Dublin. He was elected a fellow of the Royal Society in 1712. Some time before his death he gave his optical collections and papers to Dr. Robert Smith of Cambridge, inviting him to live in his house and complete his proposed investigations. The resulting work on 'Optics,' Cambridge, 1738, included a chapter by Molyneux on 'The Method of Grinding and Polishing Glasses for Telescopes,' and one begun by him but finished by John Hadley [q. v.] on 'The Casting and Polishing of Specula.' Molyneux's description of his zenith-sector and journal of the Kew observations were printed by Rigaud in 1832 among Bradley's 'Miscellaneous Works.' Subsequently to the death of Molyneux's widow, on 27 May 1730, Kew House was leased by Frederick, prince of
