James Bradley

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This article describes the English astronomer; for other people sharing the name, see James Bradley (disambiguation)

James Bradley

Born	March 1693 Sherborne, nr Cheltenham, Gloucestershire, England
Died	July 13, 1762 (aged 69) Skiveralls House, Chalford, Gloucestershire, England
Nationality	United Kingdom
Fields	Astronomy
Institutions	University of Oxford Ashmolean Museum
Alma mater	Balliol College, Oxford
Known for	Astronomer Royal
Notable awards	Copley Medal, 1748

James Bradley (March 1693 – July 13, 1762) was an English astronomer, Astronomer Royal from 1742. He is best known for discovering the aberration of light while attempting to detect stellar parallax.^[1]

[edit] Biography

Bradley was born at Sherborne, near Cheltenham in Gloucestershire, in March 1693. He entered Balliol College, Oxford, on March 15, 1711, and took degrees of B.A. and M.A. in 1714 and 1717 respectively. His early observations were made at the rectory of Wanstead in Essex, under the tutelage of his uncle, the Rev. James Pound, himself a skilled astronomer, and was elected a fellow of the Royal Society on November 6, 1718.

He took orders on becoming vicar of Bridstow in the following year, and a small sinecure living in Wales was also procured for him by his friend Samuel Molyneux. He resigned his ecclesiastical preferments in 1721, when appointed to the Savilian chair of astronomy at Oxford, while as reader on experimental philosophy from 1729 to 1760, he delivered 79 courses of lectures at the Ashmolean Museum.

Bradley worked with Samuel Molyneux until Molyneux's death in 1728 trying to measure the parallax of Gamma Draconis. However, while not finding the expected parallax, they instead found an unexplained motion which shortly after Molyneux's death Bradley realized was caused by the aberration of light.^[1] The discovery of the aberration of light which was conclusive evidence for the movement of earth and hence the correctness of Aristarchus and Kepler's theories was announced to the Royal Society in January 1729 (Phil. Trans. xxxv. 637). This aberration also allowed Bradley to accurately estimate the speed of light which had previously been shown to be finite by the work Ole Rømer and others.^[1] The observations upon which it was founded were made at Molyneux’s house on Kew Green. Bradley did not announce the supplementary detection of nutation until February 14, 1748 (Phil. Trans. xlv. I), when he had tested its reality by minute observations during an entire revolution (18.6 years) of the moon’s nodes. In 1742, he had been appointed to succeed Edmund Halley as Astronomer Royal; his enhanced reputation enabled him to apply successfully for a set of instruments costing GB£1,000; and with an 8-foot quadrant completed for him in 1750 by John Bird, he accumulated at Greenwich in ten years materials of inestimable value for the reform of astronomy. A crown pension of GB£250 a year was conferred upon him in 1752.

He retired in broken health, nine years later, to the Cotswold village of Chalford in Gloucestershire, where he died at Skiveralls House on 13 July 1762. The publication of his observations was delayed by disputes about their ownership; but they were finally issued by the Clarendon Press, Oxford, in two folio volumes (1798, 1805). The insight and industry of Friedrich Wilhelm Bessel were, however, needed for the development of their fundamental importance.

[edit] References

^ ^a ^b ^c Hirshfeld, Alan (2001). Parallax:The Race to Measure the Cosmos. New York, New York: Henry Holt. ISBN 0-8050-7133-4.

[edit] Further reading

Rigaud’s Memoir, prefixed to Miscellaneous Works and Correspondence of James Bradley, D.D. (Oxford, 1832), is practically exhaustive. Other sources of information are: New and General Biographical Dictionary, xii. 54 (1767); Biog. Brit. (Kippis); Fouchy’s Eloge, Paris Memoirs (1762), p. 231 (Histoire); Delambre’s Hist. de l’astronomie au 18e siècle, p. 413.

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.