Halley, EDMUND

Halley, EDMUND, astronomer and mathematician, was born at Haggerston, near London, 29th October 1656, educated at St Paul's School, and afterwards at Queen's College, Oxford, which he entered in 1673. Before leaving school he became an experimenter in physics, and noticed the variation of the compass. In 1676 he published a paper (in Philosophical Transactions) on the orbits of the principal planets, also observations on a spot on the sun, from which he inferred the sun's rotation on its axis. In November of the same year he went to St Helena, where he applied himself to the formation of a catalogue of the stars in the southern hemisphere, which he published in 1679 (Catalogus Stellarum Australium). Soon after his election as a Fellow of the Royal Society, he was deputed by that body to go to Danzig (1679) to settle a controversy between Hooke and Helvetius respecting the proper glasses for astronomical observations. In 1680 he was again on the Continent; with Cassini at Paris he made observations on the great comet which goes by his name (see COMET), and the return of which he predicted. After his return to England he published in 1683 (Phil. Trans.) his theory of the variation of the magnet. The next year he made the acquaintance of Newton—the occasion being his desire to find a test of a conjecture which he had made, that the centripetal force in the solar system was one varying inversely as the 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 Principia, see NEWTON. In 1686 Halley published an account of the trade-winds and monsoons on seas near and between the tropics. Two years later he undertook a long ocean voyage for the purpose of testing his theory of the magnetic variation of the compass, and embodied the results of his observations in a chart (1701). In the following year he surveyed the coasts of the English Channel, and made a chart of its tides. In 1703 he was appointed Savilian professor of Geometry at Oxford, and two years later published his researches on the orbits of the comets. On the death of Sir Hans Sloane he became (1713) secretary of the Royal Society, and held that position until 1721. During this period he made valuable experiments with the diving-bell (see DIVING). In 1720, after the death of Flamsteed, he became astronomer-royal, and his last years he spent in observing the moon through a revolution of her nodes. He died at Greenwich, 14th January 1742. His Tabulae Astronomicæ did not appear till 1749. Among his principal astronomical 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 honour of having been the first who predicted the return of a comet, and also of having recommended 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.