HALLEY, EDMUND, a celebrated astronomer and mathematician, son of a London soap-boiler, b. at Haggerston, near London, in 1656, educated at St Paul's school, and afterwards at Queen's college, Oxford, which he entered in 1673. He early became an experimenter in physics—before leaving school, he had made observations on the vari ation of the needle. In 1676 he published a paper (Philosophical Transactions) on the orbits of the principal planets; also observations on a spot on the sun, from which he inferred its rotation round its axis. In Nov. of the same year he went to St Helena, where for two years he applied himself to the formation of a catalogue of the stars in the southern hemisphere, which he published in 1679 (C«talogus Stella rum Austrait'unl). On his return he was chosen a fellow of time royal society, and deputed by that body to go to,Dantzic to settle a controversy between Hooke and Helvetius respecting the proper glasses for astronomical observations. In 1680 he made the tour of Europe, during which he made observations with Cassini at Paris on the great comet which goes by his name, and the return of which he predicted. His observations on this comet formed part of the foundation of Newton's calculation of a comet's orbit. Ilalley returned to England in 1681, and in 1683 published (Phil. Trans.) his theory of the variation of the magnet. The next year he made the acquaintance of Newton—the occasion being his desire for 'a test of a conjecture which he had made that the centripetal force in the solar system was one varying inversely as time square of the distance. He found that Newton had anticipated him, both in conjecturing and in demonstrating this fact. For an account of Halley's connection with the publication of the Princapia, see NEWTON. In 1686 Halley published an account of the trade-winds and monsoons on seas near and between the tropics, which he followed by some other chemico-meteorological papers. In 1692•he published his hypothesis relative to the change in the variations of the needle, to test the truth of which, by obtaining measures of the variations in different parts of the world, he was sent in 1698 in command of a ship to the western ocean; but his crew mutinied, and he was obliged to return. The next year, however, he sailed again
on the same expedition, and the result of his observations was given to the world in a general chart, for which he was rewarded by the rank of captain in the navy with half pay for life. Soon after he made a chart of the tides in the channel, and surveyed the coast of Dalmatia for the emperor of Austria. On the death of Dr. Wallis in 1702 he was appointed Savillian professor of geometry at Oxford. In 1705 lie published his researches on the orbits of the comets. In 1713, on the death of Sir Hans Sloane, he became secretary of the royal society; in 1716 he made valuable experiments with the diving-bell, which were afterwards published; and in 1720, after the death of Flamsteed, he became astronomer-royal, and continued without assistance to conduct the operations at the observatory with unremitting energy. In this office, and engaged especially in studying the moon's motions, he passed the rest of his life. In 1729 he was chosen a foreign member of the academy of sciences, Paris. He died at Greenwich, Jan. 14, 1742, 86 years old. Halley had married, in 1686. a daughter of Mr. Tooke, auditor of exchequer, by whom he had several children. Besides the writings mentioned, Halley wrote many others. His Tabula Ath'07}077AkCE did not appear till 1749. Among his principal discoveries may be mentioned that of the long inequality of Jupiter and Saturn, and that of the slow acceleration of the moon's mean motion. He has the honor of having been the first who predicted the return of a comet, and also of having recom mended the observation of the transits of Venus with a view to determining the sun's parallax—a method of ascertaining the parallax first suggested by James Gregory.