EDMUND HALLEY, (1656-1742), an eminent astro-nomer, was born at Haggerston, near London, October 29, 1656. His father, a wealthy soapboiler, desiring to give his only son an education suitable to his promising genius, placed him at St Paul's School, where he was equally dis-tinguished for classical as for mathematical ability. Before leaving it for Queen's College, Oxford, which he entered as commoner in 1673, he had observed the change in the variation of the compass, and, at the age of nineteen, he supplied a new and improved method of determining the elements of the planetary orbits. His detection of consider-able errors in the tables then in use led him to the con-clusion that a more accurate ascertainment of the places of the fixed stars was indispensable to the progress of astronomy; and, finding that Flamsteed and Hevelius had already undertaken to catalogue those visible in northern latitudes, he assumed to himself the task of making observa-tions in the southern hemisphere. A recommendation from Charles II. to the East India Company procured for him an apparently suitable, though, as it proved, ill-chosen station, and in November 1676 he embarked for St Helena. On the voyage he noticed the retardation of the pendulum in approaching the equator: and during his stay on the island he observed the transit of Mercury, which sug-gested to him the important idea of employing similar phenomena for the calculation of the solar distance. He returned to England in November 1678, having by the registration of 360 stars won the title of the " Southern Tycho," and by the translation to the heavens of the " Royal Oak," earned a degree of master of arts, conferred at Oxford by the king's command December 3, 1678, almost simultaneously with his election as fellow of the Royal Society. Six months later, the indefatigable astro-nomer started for Dantzic to set at rest a dispute of long standing between Hooke and Hevelius as to the respective merits of plain or telescopic sights; and towards the end of 1680 he proceeded on a Continental tour. In Paris he observed with Cassini the great comet of 1680 after its perihelion passage; and having returned to England, he married in 1682 Mary, daughter of Mr Tooke, auditor of the exchequer, with whom he lived harmoniously for fifty-five years. He now fixed his residence at Islington, engaged chiefly upon lunar observations, with a view to the great desideratum of a method of finding the longitude at sea. His mind, however, was also busy with the momentous pro-blem of gravity. Having reached so far as to perceive that the central force of the solar system must decrease inversely as the square of the distance, and applied vainly to Wren and Hooke for further elucidation, he made in August 1684 that journey to^Cambridge for the purpose of consulting Newton, which resulted in the publication of the Principia. The labour and expense of passing this great work through the press devolved upon Halley, who also wrote the prefixed hexameters ending with the well-known line— Nec fas est propius mortali attingere divos.
In 1696 he was, although a zealous Tory, appointed comp-troller of the mint at Chester, and (August 19, 1698) he received a commission as captain of the "Paramour Pink:' for the purpose of making extensive observations on the conditions of terrestrial magnetism. This task he accomplished in a voyage which lasted two years, and extended to the 52d degree of S. latitude. The results were published in a General Chart of the Variation of the Gompass in 1701; and immediately afterwards heexecuted byroyal com-mand a careful survey of the tides and coasts of the British Channel, an elaborate map of which he produced in 1702. On his return from a journey to Dalmatia, for the purpose of selecting and fortifying the port of Trieste, he was nominated, November 1703, Savilian professor of geometry at Oxford, and received an honorary degree of doctor of laws. Between 1713 and 1721 he acted as secretary to the Boyal Society, having previously during eight years (1685-93) filled the same office, and early in 1720 he succeeded Flamsteed as astronomer-royal. Although in his sixty-fourth year, he undertook to observe the moon through an entire revolution of her nodes (eighteen years), and actually carried out his purpose. He died in the full possession of his faculties, January 14, 1742, at the age of eighty-five.

Halley's most notable scientific achievements were—his detection of the "long inequality " of Jupiter and Saturn, and of the acceleration of the moon's mean motion; his discovery of the proper motions of the fixed stars; his theory of variation, including the hypothesis of four magnetic poles, revived by Hansteen in 1819, and his suggestion of the magnetic origin of the aurora borealis ; his calculation of the orbit of the 1682 comet (the first ever attempted), coupled with a prediction of its return, strikingly verified in 1759 and 1835 ; and his indication (in 1716, Phil. Trans., No. 348) of a method still used for determining the solar parallax by means of the transits of Venus.

His principal works are Catalogus Stellarum Australium, London, 1679, the substance of which was embodied in vol. iii. of Flamsteed's Historia Coelestis, 1725 ; Synopsis Astronomies Cometiae, Oxford, 1705 ; Astronomical Tables, London, 1752 ; also eighty-one mis-cellaneous papers of considerable interest, scattered through the Philosophical Transactions. To these should be added his version from the Arabic (which language he acquired for the purpose) of the treatise of Apollonius De sectione rationis, with a restoration of his two lost books De sectione spatii, both published at Oxford in 1706; also his fine edition of the Conies of Apollonius, with the treatise by Serenus De sectione cylindri et coni, Oxford, 1710, folio. His edition of the Spherics of Menelaus was published by his friend Dr Costard in 1758.