NEVIL

MASKELYNE (1732-1811)  , English astronomer-royal, was born in London on the 6th of October 1732 . The solar eclipse of 1748 made a deep impression upon him; and having graduated as seventh wrangler from Trinity College, Cambridge, in 1754, he determined to devote himself wholly to astronomy . He became intimate with James Bradley in 1755, and in 1761 was deputed by the Royal Society to make observations of the transit of Venus at St Helena . During the voyage he experimented upon the determination of longitude by lunar distances, and ultimately effected the introduction of the method into navigation (q.v.) . In 1765 he succeeded Nathaniel Bliss as astronomer-royal . Having energetically discharged the duties of his office during forty-six years, he died on the 9th of February 1811 . Maskelyne's first contribution to astronomical literature was " A Proposal for Discovering the Annual Parallax of Sirius," published in 176o (Phil . Trans. li . 889) . Subsequent volumes of the same series contained his observations of the transits of Venus (1761 and 1769), on the tides at St Helena (1762), and on various astronomical phenomena at St Helena (1764) and at Barbados (1764) . In 1763 he published the British Mariner's Guide, which includes the suggestion that in order to facilitate the finding of longitude at sea lunar distances should be calculated beforehand for each year and published in a form accessible to navigators . This important proposal, the germ of the Nautical Almanac, was approved of by the government, and under the care of Maskelyne the Nautical Almanac for 1767 was published in 1766 .

He continued during the

remainder of his life the superintendence of this invaluable annual . He further induced the government to print his observations annually, thereby securing the prompt dissemination of a large mass of data inestimable from their continuity and accuracy . Maskelyne had but one assistant, yet the work of the observatory was perfectly organized and methodically executed . He introduced several practical improvements, such as the measurement of time to tenths of a second; and he prevailed upon the government to replace Bird's mural quadrant by a repeating circle 6 ft. in diameter . The new instrument was constructed by E . Troughton; but Maskelyne did not live to see it completed . In 1972 he suggested to the Royal Society the famous Schehallion experiment for the determination of the earth's density and carried out his plan in 1774 (Phil . Trans . 1 . 495), the apparent difference of latitude between two stations on opposite sides of the mountain being compared with the real difference of latitude obtained by triangulation . From Maskelyne's observations Charles Hutton deduced a density for the earth 4.5 times that of water (ib. lxviii . 782) .

Maskelyne also took a

great interest in various geodetical operations, notably the measurement of the length of a degree of latitude in Maryland and Pennsylvania (ibid. lviii . 323), executed by Mason and Dixon in 1766-1768, and later the determination of the relative longitude of Greenwich and Paris (ib. lxxvii . 151) . On the French side the work was conducted by Count Cassini, Legendre, and Mechain; on the English side by General Roy . This triangulation was the beginning of the great trigonometrical survey which has since been extended all over the country . His observations appeared in four large folio volumes (1776-1811) . Some of them were reprinted in S . Vince's Astronomy (vol. iii.) . (A . M .