BRADLEY, James, English astronomer: b. Sherborne, Gloucestershire, 1693; d. Chal ford, Gloucestershire, 13 July 1762. He was educated at Balliol College, Oxford, and took orders, but his taste for astronomy soon led him in a different direction, and in 1721 he was appointed Savilian professor of astronomy at Oxford. Seven years afterward he made known his discovery of the aberration of light. But although this discovery gave a greater degree of accuracy to astronomical observations, yet slight differences remained which he studied during 20 years with the greatest perseverance, and finally discovered that they were fully ex plained by the supposition of an oscillating motion of the earth's axis, completed during revolution of the moon's nodes, that is, in about 18 and a half years. He called this phe nomenon the anutation of the earth's axisp ; and published his account of it in 1748, for which he received the Copley medal. By these two discoveries astronomers were, for the first time, enabled to make tables of the motions of the heavenly bodies with the necessary accuracy.
Bradley had already, in 1726, explained the method of obtaining the longitude by means of the eclipse of Jupiter's first satellite. In 1742, at the death of Dr. Halley, he received the office of astronomer royal, and removed to the ob servatory at Greenwich. Here he spent the re mainder of his life, entirely devoted to astro nomical studies. His observations in manu script appeared under the title of (Astronomical Observations made at the Observatory at Greenwich, 1750-62> (1798, 1805). From this rich mine have been taken thousands of obser vations on the sun, moon and planets of the highest astronomical value. The value of these observations was enormously increased by Bes se!, who undertook their systematic reduction and extracted from them the catalogue of 3,222 stars which he published under the title of (Fundaments Astronomia.)