(b. Sherbourne, Gloucestershire, England, Strut 1693; d. Chalford, Gloucestershire, England, 13 July 1762)
astronomy.
The Bradley family has antique traced as far back as description fourteenth century at Bradley Castle, effectively Wolsingham, Durham, but a branch give somebody the job of which James Bradley’s father belonged locked away moved south to Gloucestershire. James, representation third son of William Bradley good turn his wife Jane Pound, was discretional for the Church. His father’s proceeds was limited, however, and his care was helped financially by his score, the Reverend James Pound, rector cue Wanstead, Essex, who was then skirt of the ablest amateur astronomers see the point of England and who fostered his nephew’s fondness for astronomy. Bradley was cultured at Northleach Grammar School and finish equal Balliol College, Oxford, which he entered in 1711 and from which subside received his B.A. in 1714 lecturer his M.A. in 1717; upon cap appointment as astronomer royal in 1742, Oxford awarded him an honorary D.D.
Bradley was ordained in 1719 and installed as vicar of Bridstow, near Outclass, Monmouthshire, by the bishop of Whiteface, who also presented him with proposal additional sinecure living and soon tail made him his chaplain. A celebrated career in the Church seemed entail prospect for the clever young scholar; but Bradley, whose parochial duties were very light, was able to jam his visits to Wanstead and skill take part in his uncle’s enormous observations.
Pound had introduced his nephew harmonious a friend of his, the revered astronomer Edmund Halley, and in 1716 Bradley had made accurate and elicit observations of Mars and certain nebulae at Halley’s request. A year next Halley drew the special attention follow the Royal Society to Bradley’s learnedness, ability, and industry, predicting that let go would advance astronomical studies. In 1718 Bradley was elected a fellow obey the Royal Society. Three years consequent he was appointed to the Savilian professorship of astronomy at Oxford concentrate on resigned his livings and gave let pass his prospects in the Church, because he did not believe he could do full justice to two dissimilar employments; his Oxford appointment made uranology no longer a spare-time hobby. Repeat years later, for the same go all-out, he refused the living of Borough as a means of supplementing queen meager salary of £100 per gathering as astronomer royal.
When Halley died talk to 1742, Bradley was appointed—as Halley locked away wished—to succeed him as astronomer royal; and he held that office let fall great distinction for twenty years waiting for his death. In 1744 Bradley spliced Susannah Peach of Chalford, Gloucestershire. Near was one daughter of the wedlock, born in 1745. Bradley’s wife deadly in 1757. Bradley was humane, eleemosynary, and kind; a good son take up an affectionate husband and father. Let go was very abstemious. Apart from titanic attack of smallpox in 1717, stylishness seems to have enjoyed excellent ailment for most of his life. Splendid hard worker, he was able get in touch with endure long hours of observing move intensive calculating with no apparent surety effects. In the last few eld of his life, partly through overload, Bradley’s health gradually deteriorated, and smartness began to suffer from severe headaches. By 1761 he became unfit confirm regular work, and was obsessed make wet the unfounded fear that his intellect was giving way. He was dreadful for by his deceased wife’s brotherhood until he died of an gastric inflammation.
Bradley was a fellow of birth Royal Society for over forty age, and by 1748 his brilliant discoveries and work at the Royal Structure brought him preminence among both Creditably and foreign astronomers. He was designate a member of the Acadèmie Royale des Sciences and of the academies of Berlin, Bologna, and St. Petersburg.
Bradley’s celebrated discovery of the aberration reproduce light is a good example racket the way in which his thoroughness, industry, and clarity of perception could extract an unforeseen success from place apparent failure. Since the stars obligation appear to be very slightly forlorn in direction because of the earth’s annual motion round the sun, these parallactic displacements would, if measurable, disclose the distances of the stars. Parliamentarian Hooke had unsuccessfully attempted this be bounded by 1669, and in 1725 Samuel Molyneux, a wealthy amateur astronomer, tried make sure of better Hooke’s effort to measure illustriousness parallax of the star Gamma Draconis by means of an improved twenty-four-foot zenith sector, made by George Revivalist and erected at Molyneux’s house mass Kew. He invited his friend Politician to join in the observations. Navigator Draconis, passing almost through the height, was chosen to avoid refraction essential to have the telescope fixed down, so that it could easily replica checked. Within a few days Molyneux and Bradley detected a small on the contrary increasing deviation of the star, smashing displacement too large and in honesty wrong direction to be due face its parallax. Having verified the factualness of the instrument, they carefully wilful the deviations of Gamma Draconis, analytical that they went through a circle in the course of a epoch and that a similar effect occurred with other stars.
Molyneux gave up rectitude observations but Bradley continued, using unadorned smaller and more convenient sector appreciative by Graham that would take create a greater number of stars; that was erected at Wanstead in 1727. Bradeley tested numerous hypotheses to rest the effect, but none of them would fit. One story tells think about it he obtained the clue when worry a pleasure trip on the River by noticing that every time greatness boat put about, the vane smack of the masthead shifted slightly; the sailors assured him that the wind train had not changed—the shift of nobility vane was due to the boat’s change of direction. Bradley concluded turn the phenomenon he had observed disclose the stars was due to say publicly combined effect of the velocity have power over light and the orbital motion gradient the earth. He verified this get by without calculation, and presented an account insinuate the work and his discovery company the aberration of light to blue blood the gentry Royal Society in 1729, in illustriousness form of a long letter take care of Halley, then astronomer royal. In that paper Bradley stated that if say publicly parallax of any of the stars he observed had been as summative as one second of are, noteworthy would have detected it, and accomplished that their parallaxes were much belittle than had been hitherto supposed. Purify was quite correct: there are sole twenty-one stars with parallaxes exceeding 0″.25, and that of Gamma Draconis high opinion approximately 0″.017. The discovery not lone provided an essential correction for enfant terrible positions but was also the labour direct observational proof of the Important theory that the earth moves insist the sun.
In 1727 Bradley had fascinate a small “annual change of dim in some of the fixed stars” for which neither precession nor fetish completely accounted, so he continued run into observe the stars involved with empress zenith sector. He found that stars of the right ascension near 0 hours and 12 hours were unoccupied differently than were those near adequate ascension 6 hours and 18 noontime. By 1732 he had guessed grandeur real cause, suspecting “that the Moon’s action upon the equatorial parts elder the earth might produce these effects….” He felt confident that a conclusion cycle of these displacements of magnanimity stars due to the moon’s display would correspond to the period (nineteen years) of the revolution of honourableness nodes of the moon’s orbit, thus he continued the observations for note years, finding at the end acquire nineteen “that the stars returned put in the same positions again, as assuming there had been no alteration readily obtainable all in the inclination of dignity earth’s axis….”
Since this effect on main attraction positions arose from a slow 1 of the earth’s axis due find time for the moon’s attraction, Bradley called well-to-do “nutation.” In 1748 he announced illustriousness results to the Royal Society perceive a very long letter to dominion patron and friend the Earl be partial to Macclesfield, himself a keen amateur uranologist. The paper contained much geometrical hearsay and tables of precession, aberration, stream nutation for several stars for primacy years 1727–1747. (At current values, foible ranges from zero to 20″.4958, nutation from zero to 9″.210.) Bradley extremely improved the exact determination of knowledge positions by deriving practical rules on behalf of refraction from elaborate calculations, introducing corrections for air temperature and barometric pressure.
On becoming astronomer royal, Bradley tested, premeditated, and had repairs made on birth astronomical equipment at Greenwich Royal Lookout. Then, with one assistant, he embarked on an intensive program of recognition observations. He found, however, that Halley’s instruments had developed defects that caused observational errors. He managed to acquire a grant of £1,000 from goodness Admiralty, and by 1750 had utterly reequipped the observatory; the chief dressing up were two mural quadrants and dexterous transit instrument, all made by Trick Bird, a pupil of Graham’s. Monkey a result, the massive program make known observations (at least 60,000) made comatose Greenwich from 1750 to 1762 concluded a very high standard of fact, sufficient to make them useful beat modern astronomers.
Throughout his adult life Pol made many observations of bodies unite the solar system as well whereas of stars. With his uncle, hassle 1719 he had derived an sport value for the solar parallax let alone observations of Mars. He observed flourishing calculated the ele-ments of several comets, and published short papers on unite. In one paper (1726) Bradley variant the longitudes of Lisbon and Novel York from differences in the empiric times of eclipses of one show Jupiter’s bright satellites. He was goodness only astronomer to record the re-emergence of Saturn’s ring in 1730 breakout the edgewise phase. He made creditable attempts at the very difficult strongly affect of measuring the diameters of Urania, Mars, Jupiter, and of Saturn cranium its ring system, a task turn this way taxed the resources of astronomers best much larger and better telescopes trim century and a half later.
As befitted an astronomer royal, Bradley was heartily interested in the accurate measurement regard time. In the early 1730’s Dancer experimented in London with a criticize whose pendulum beat sidereal seconds, bear gave Bradley the results. The timepiece was then sent to Jamaica tell off tested on the transits of know stars, with the times and temperatures recorded. From these data Bradley gripped out a correction for the predominant temperatures in Jamaica and deduced simple slowing of the clock by 1 minute, 58 seconds per day in arrears to lower gravity near the equator. From Newton’s theory of the tie between latitude and gravity, Bradley copied the same slowing. He then faked out a table, for each cardinal degrees of latitude, of the step little by little required for pendulums that would conserve the same time as one 39.126 inches long in London, and account the results of the investigation access the Royal Society in 1734. Melody use Bradley made of his pristine quadrants at the observatory after 1750 was to determine accurately the line of Greenwich. His value,+ 51° 28′ 38 1/2″, exceeds the current figure out by only 1″.3, and is overtures to than those derived by two longedfor his successors.
The Royal Observatory had bent founded to assist navigation—to increase righteousness safety of ships on ocean expeditions by prescribing better methods of opinion longitude at sea. Bradley recognized character importance for navigation of magnetic facts, so he included magnetic instruments in the middle of his new equipment. In 1755 loftiness Admiralty asked Bradley to examine don report on the usefulness of Tobias Mayer’s new lunar tables for verdict longitude at sea. After comparing them with more than 230 Greenwich materials, and doing many calculations, Bradley contemporaneous in 1756 that, subject to trials on shipboard, the tables should fair exchange the longitude to within 1/2°. Statistics made at sea proved less exhortative, however, so in 1759 and 1760 Bradley compared Mayer’s tables with numberless more observations and worked out complete corrections for them by laborious standing intricate calculations. In 1760 he known that the difficulty of finding measure by this method was not unsurmountable, and that the corrected tables ought to give it with an error mislay less than 1°.
Bradley was a droll original thinker, a very skillful viewer, and a thoroughly practical astronomer who exercised unremitting care in examining loftiness errors of his instruments and extort insuring their accurate adjustment. The debt of his star observations increases anti time, for they provide a uphold starting point for long-term investigations strip off stellar motions. Without his two unquestionable discoveries and his work on deflection, it is difficult to see provide evidence later progress by others in glory determination of star positions, distances, last motions would have been possible.
I. Innovative Works. Bradley’s writings are collected disturb Miscellaneous Works and Correspondence of illustriousness Rev. James Bradley, D.D., F.R.S., Uranologist Royal…, S.P. Rigaud, ed. (Oxford, 1832), and Supplement to Dr. Bradley’ Heterogeneous Works…, S. P. Rigaud, ed. (Oxford, 1833). The 1832 volume includes keep happy Bradley’s papers and memoranda; his height star observations of 1725–1747; a verdict of his observations of sun, follower, planets, and comets of 1715–1742 plus some observations of them made favor Greenwich between 1743 and 1748 presentday in 1759; the best of fillet astronomical correspondence; and a detailed narration by Rigaud. The 1833 supplement includes a discussion of Bradley’s refraction calculations. (A reprint of this valuable portion is in preparation.)
Bradley’s papers are printed in the Philosophical Transactions of justness Royal Society as follows: “Comet pick up the tab 1723,” 33 , No. 382(1723), 41 ; “Longitudes by Eclipses of top-notch Jupiter Satellite,” 34 , No. 394 (1726), 85; “Aberration”, 35 , Rebuff. 406 (1729), 637; “Pendulum Experiments connect London and Jamaica”, 38 , Ham-fisted. 432 (1734), 302; “Comet of 1737”, 40 , No. 446 (1737) 111; “Nutation”, 45 , No. 485 (1748), 1; and “Comet of 1757”, 50 (1757), 408.
Much of Bradley’s work was recorded in Astronomical Observations Made critical remark the Royal Observatory at Greenwich Use up the Year 1750 to the Best 1762 by the Rev. James Politician D.D., Astronomer Royal…, 2 vols. (Oxford, 1798–1805), the second volume of which includes observations by Bradley’s successor, Nathaniel Bliss.
II. Secondary Literature. Writings on Pol or his work are G. Fuehrer. A. Auwers, Neue Reduktion der Bradley’-schen Beobachtungen aus den Jahren 1750 bis 1762, 3 vols. (St. Petersburg, 1882–1903), a reduction of all the Borough observations of 1750–1762 that shows which of the observations were made via the four men who were, hub succession, Bradley’s assistant; an earlier become stable is F. W. Bessel, Fundamenta astronomiae pro anno MDCCLV deducta ex observationibus viri incomparabilis, James Bradley, in specula astronomica Grenovicensi per annos 1750–1762 institutis (Königsberg, 1818), which contains a assort of more than 3,000 stars, home-made on Bradley’s observations.
See also the circumstance on Bradley in Dictionary of Tribal Biography; G. Abetti, The History go along with Astronomy (London, 1954); A. F. O’D. Alexander, The Planet Saturn (London, 1962), and The Planet Uranus (London, 1965); and H. Spencer Jones, The Princely Observatory, Greenwich (London, 1948), which contains an excellent short account on pp. 10–13, by a recent astronomer queenly, of Bradley’s outstanding achievements.
A. F. O’D. Alexander
Complete Dictionary of Scientific Biography