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HORNSBY, THOMAS, D.D. (1733–1810), astronomer, son of Thomas Hornsby of Durham, was born at Oxford on 28 Aug. 1733. He matriculated in Corpus Christi College, Oxford, on 1 Dec. 1749, took degrees of B.A. and M.A. respectively in 1753 and 1757, was elected a fellow of his college, and created D.D. by diploma on 22 June 1785. In 1763 he succeeded James Bradley [q. v.] in the Savilian chair of astronomy, and as ‘an instance of reformation’ in the university, was obliged to go through a yearly course of lectures. He was admitted a fellow of the Royal Society on 21 April 1763. Immediately on his appointment in 1772 as the first Radcliffe observer, he laid the foundation-stone of the present observatory, which was not completed until 1794. Its equipment (the finest of that time) included two quadrants and a transit-instrument, each of eight feet, a zenith sector, an equatoreal, and a Dollond's achromatic refractor, to which a Newtonian reflector by Sir William Herschel was added later. The outlay upon buildings and instruments amounted to 28,000l. A regular series of transit-observations was made there as long as Hornsby lived. After his appointment, however, in 1782 to the Sedleian professorship, much of his attention was taken up with his excellent series of lectures on experimental philosophy; and he became Radcliffe librarian as well in 1783. Hornsby died at Oxford on 11 April 1810, aged 76. His two sons, Thomas (1766–1832) and George (1781–1837), both graduated from Christ Church, Oxford. The former was vicar of Ravensthorpe, Northamptonshire, from 1797 till death; the latter vicar of Turkdean, Gloucestershire, from 1809 till death.

Hornsby observed the transit of Venus of 6 June 1761 at Shirburn Castle, that of 3 June 1769 at Oxford, and deduced from both a solar parallax (8″.78) almost identical with the best modern results. He took an active share in the scientific pursuits of the Earl of Macclesfield. Five papers by him were read before the Royal Society, viz.: 1. ‘A Discourse on the Parallax of the Sun’ (Phil. Trans. liii. 467). 2. ‘On the Transit of Venus in 1769’ (ib. lv. 326). 3. ‘An Account of the Observations of the Transit of Venus and of the Eclipse of the Sun, made at Shirburn Castle and at Oxford’ (ib. lix. 172). 4. ‘The Quantity of the Sun's Parallax as deduced from the Observations of the Transit of Venus on 3 June 1769’ (ib. lxi. 574). 5. ‘An Inquiry into the Quantity and Direction of the Motion of Arcturus’ (ib. lxiii. 93). He remarked in 1798 the common proper motion of the stars of Castor, but failed to infer their physical connection (Grant, History of Astronomy, p. 559). The first volume of Bradley's ‘Astronomical Observations’ was edited by him for the Clarendon Press in 1798. He had undertaken the task more than twenty years previously, and the delay, for which he was acrimoniously censured, was due to his ill-health.

[Foster's Alumni Oxonienses, ii. 693; Honours Register (1883), pp. 89, 123, 491; Gent. Mag. 1810, pt. i. p. 494; The Georgian Era, iii. 490 (1834); Nichols's Lit. Anecd. iii. 707, viii. 232, 260; Nichols's Illustr. of Lit. iv. 516, 787; André et Rayet's L'Astronomie Pratique, i. 53; Lalande's Bibl. Astronomique, p. 484; Poggendorff's Biog. Lit. Handwörterbuch; Mädler's Gesch. der Astronomie, i. 465, 470, 472, 489; Bradley's Misc. Works, Preface (Rigaud); Watt's Bibl. Brit.]

A. M. C.