Halley, Edmond 1656-1742
English astronomer and mathematician

Born in London, he was educated at St Paul's School and Queen's College, Oxford. He left for St Helena in 1676 to make the first catalogue of the stars in the southern hemisphere (Catalogus Stellarum Australium, 1679). In 1680 he was in Paris with Giovanni Cassini, observing comets, and his calculation of the orbital parameters of 24 comets enabled him to predict correctly the return (in 1758, 1835 and 1910) of a comet that had been observed in 1583 (Halley's comet). He was the first to make a complete observation of the transit of Mercury and the first to recommend the observation of the transits of Venus in order to determine the Sun's parallax. He established the mathematical law connecting barometric pressure with heights above sea level (on the basis of Boyle's law). He published studies on magnetic variations (1683), trade winds and monsoons (1686), investigated diving and underwater activities, and voyaged in the Atlantic Ocean to test his theory of the magnetic variation of the compass, which he embodied in a magnetic sea chart (1701). Halley predicted with considerable accuracy the path of totality of the solar eclipse that was observed over England in 1715, and was the first to realize that the Moon's mean motion had a secular acceleration. He also noticed that stars such as Aldebaran, Acturus and Sirius had a proper motion and that they had gradually changed their positions over the previous two millennia. In map-making he was the first to use an isometrical representation. He was also the first to predict the extraterrestrial nature of the progenitors of meteors. He encouraged Isaac Newton to write his celebrated Principia Mathematica (1687) and paid for its publication himself. With his Breslau Table of Mortality (1693) he laid the actuarial foundations for life insurance and annuities. In 1703 he was appointed Savilian Professor of Geometry at Oxford, where he built an observatory on the roof of his house which survives today, and in 1720 he succeeded John Flamsteed as Astronomer Royal of England.

Bibliography: C A Ronan, Edmond Halley: Genius in Eclipse (1969)