James Bradley
English astronomer and priest, third Astronomer Royal.
James Bradley (September 1692 – 13 July 1762) was an English astronomer and Anglican priest who became the third Astronomer Royal in 1742. His lasting fame rests on two major astronomical discoveries: the aberration of light, identified between 1725 and 1728, and the nutation of Earth’s axis, which he worked out from 1728 to 1748.
The French astronomer and historian Jean Baptiste Joseph Delambre called these findings “the most brilliant and useful of the century.” In his 1821 *History of astronomy in the 18th century*, Delambre wrote that modern astronomy owes its precision to these two discoveries, and that they place Bradley second only to Hipparchus and Kepler, above all other astronomers of any era or nation.
Bradley was born in September 1692 in Sherborne, near Northleach, Gloucestershire, to William Bradley and Jane Pound. He attended Westwood’s Grammar School in Northleach, then entered Balliol College, Oxford, on 15 March 1711, earning a Bachelor of Arts in 1714 and a Master of Arts in 1717. His first astronomical work was done at the rectory of Wanstead in Essex, under the guidance of his uncle James Pound, a skilled astronomer. Bradley was elected a fellow of the Royal Society on 6 November 1718. The following year he was ordained and became vicar of Bridstow in Herefordshire; his friend Samuel Molyneux also secured him a small sinecure in Wales. He gave up these church positions in 1721 when he was appointed to the Savilian chair of astronomy at Oxford. From 1729 to 1760 he also served as reader in experimental philosophy, delivering 79 lecture courses at the Ashmolean Museum.
In 1742 Bradley succeeded Edmond Halley as Astronomer Royal. His reputation allowed him to secure a set of instruments costing £1,000. With an 8-foot quadrant finished in 1750 by John Bird, he gathered at Greenwich over ten years a body of observations invaluable for reforming astronomy. A crown pension of £250 a year was granted to him in 1752. Nine years later, his health failing, he retired to the Cotswold village of Chalford in Gloucestershire. He was treated by a local doctor and by Daniel Lysons from Oxford. Bradley died at Skiveralls House on 13 July 1762 and was buried in the churchyard of Holy Trinity church in Minchinhampton, Gloucestershire. His wife had died in 1757; he was survived by one daughter.
In 1722 Bradley m
- born
- September 1692, Sherborne, near Northleach, Gloucestershire
Lore & Background
Bradley was born to William Bradley and Jane Pound in September 1692. After attending Westwood's Grammar School at Northleach, he entered Balliol College, Oxford, on 15 March 1711, earning a Bachelor of Arts in 1714 and a Master of Arts in 1717. His early observations were made at the rectory of Wanstead in Essex under his uncle James Pound, a skilled astronomer. Bradley was elected a fellow of the Royal Society on 6 November 1718. He took orders as vicar of Bridstow in Herefordshire in 1719, and a small sinecure living in Wales was procured for him by his friend Samuel Molyneux. He resigned his ecclesiastical preferments in 1721 when appointed Savilian professor of astronomy at Oxford. From 1729 to 1760, he delivered 79 courses of lectures on experimental philosophy at the Ashmolean Museum.
In 1742, Bradley succeeded Edmond Halley as Astronomer Royal. His reputation enabled him to apply successfully for instruments costing £1,000, and with an 8-foot quadrant completed 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 £250 a year was conferred upon him in 1752. Bradley retired in broken health nine years later to the Cotswold village of Chalford in Gloucestershire, where he had medical attention from a local doctor and Daniel Lysons from Oxford. He died at Skiveralls House on 13 July 1762 and was buried in the churchyard of Holy Trinity church, Minchinhampton. His wife died before him in 1757, and he was survived by one daughter.
Reader's Guide
Bradley's discoveries of the aberration of light and nutation of the Earth's axis were called 'the most brilliant and useful of the century' by historian of astronomy Jean Baptiste Joseph Delambre. In his 1821 History of astronomy in the 18th century, Delambre stated: 'It is to these two discoveries by Bradley that we owe the exactness of modern astronomy. ... This double service assures to their discoverer the most distinguished place (after Hipparchus and Kepler) above the greatest astronomers of all ages and all countries.' The aberration of light provided conclusive evidence for the Earth's orbital motion and gave the first accurate determination of the speed of light, expressed as 8 minutes 12 seconds for light to travel from the Sun to Earth. Bradley's observations, though delayed in publication due to disputes, were finally issued by the Clarendon Press in two folio volumes (1798, 1805), and the German astronomer Friedrich Wilhelm Bessel was needed to develop their fundamental importance.
Did You Know?
- Bradley measured the angular diameter of Venus in 1722 using a large aerial telescope with an objective focal length of 212 ft (65 m).
- His discovery of the aberration of light occurred while attempting to detect stellar parallax of Gamma Draconis, working with Samuel Molyneux until Molyneux's death in 1728.
- A story, probably apocryphal, says the solution to the aberration occurred to Bradley while on a sailing boat on the River Thames, noticing a flag at the mast top change direction when the boat turned.
- Bradley's published value for the speed of light was only about 1.3% too high.
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