HALLEY, hAl'i, Edmund, English mathe matician and astronomer: b. Haggerston, near London, 8 Nov. 1656; d. Greenwich, 14 Jan. 1742,. He was eduCated at Queen's College, Oxford. Before 'he was 19 he published 'A Direct Geometrical, Method of Finding the Aphelia and Eccentricity of Planets,' which Supplied a defect in the Keplerian theory of planetary,motion. By some observations on a spot which appeared on the sun's disc in July and August 1676, he established the certainty of the motion of the sun round its own axis. On 21 August, the same year, he fixed the longi tude of the Cape of Good Hope by his observa tion of the occultation of Mars by the moon. In 1679 he published 'Catalogus Stellarum Aus tralium,' and in 1683 his 'Theory of the Varia tion of the Magnetical COmpass,) in which he endeavors to account for that phenomenon by the supposition of the whole globe of the earth being one great magnet, having four circulating magnetical poles or points of attraction. For the purpose ,of making further observations rel ative to the variation of the compass he set sail on a voyage in 1699, and having traversed both hemispheres arrived in England in Sep tember 1700. The spot at Saint Helena where
he erected a tent for making astronomical ob servations is still called Halley's Mount. As the result of his researches he published a general chart, showing at one view the variation of the compass in all those seas with which English navigators were acquainted. He was next employed to observe the course of the tides• in the English Channel, with the longi tudes and latitudes of the principal headlands, in consequence of which he published a large Map of the Channel. In 1703 he was elected Savilian professor of geometry at Oxford, and in 1721 he received the appointment of astron omer-royal at Greenwich, where he afterward resided, devoting his time to completing the theory of the motion of the moon. In the same year he !began Ms•nbsetvations, and for the space of 18 years scarcely ever missed taking a meridian view of the moon when the weather was not unfavorable. In 1752 ap. (feared his 'Astronomical Tables' ; and he was the author of a great number of papers in the !-Philosophical Transactions.' For the comet Wind by.his, name, 'see COMT.