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MACLEAR, Sir THOMAS (1794–1879), astronomer, was the eldest son of James Maclear of Newtown Stewart, co. Tyrone, where he was born on 17 March 1794. His refusal to enter the church led to a breach with his father, and he was sent to England in 1808 to be educated for the medical profession, under the care of his maternal uncles, Sir George and Dr. Thomas Magrath. Having studied in Guy's and St. Thomas's Hospitals, and passed distinguished examinations, he was admitted in 1815 a member of the Royal College of Surgeons, under the presidency of Sir William Blizard. He then accepted the post of house-surgeon to the Bedford Infirmary, where he became acquainted with Admiral Smyth, and studied astronomy and mathematics. In 1823 he entered into partnership with his uncle at Biggleswade in Bedfordshire, and married in 1825 Mary, daughter of Mr. Theed Pearse, clerk of the peace for that county. The Astronomical Society lent him in 1829 the Wollaston telescope for the purpose of observing a series of occupations of Aldebaran, calculated by himself, and he set it up with a thirty-inch transit in a small observatory in his garden at Biggleswade (Memoirs of Royal Astr. Society, vi. 147). Succeeding Thomas Henderson [q. v.] in 1833 as royal astronomer at the Cape of Good Hope, he arrived there on 5 Jan. 1834, ten days before Sir John Herschel, whose zealous co-operator and attached friend he became.

Maclear was indefatigable in the duties of his office. His activity, indeed, as an observer outran the computing powers of his small staff, and most of the valuable materials he had accumulated were left by him unreduced. He published, however, in 1840 a volume of observations made in 1834. From 1837 he was occupied with the remeasurement and extension of Lacaille's arc. The field operations, conducted with remarkable skill and energy in the midst of most deterrent difficulties, were completed in 1847, and the results appeared in two 4to volumes, edited by Sir George Airy, in 1866. For this great work, still fundamental in the survey of the colony, Maclear received the Lalande prize in 1867 and a royal medal in 1869. Bradley's zenith-sector was sent out to the Cape for use in the arc-measurement, and returned uninjured to Greenwich in 1850. A seven-inch equatorial by Merz was mounted at the Cape in 1849, and a large transit-circle, a facsimile of that at Greenwich, in 1855. Maclear's determinations of α Centauri in 1839-40 and 1842-8 confirmed Henderson's parallax of about one second (ib. xii. 329). He observed the maximum of η Argus in 1843, and the meteoric shower of 1866. His cometary observations, regularly communicated to the Astronomical Society, were of great value. They included prolonged series on Halley's and Donati's comets, besides numerous places of Encke's, Petersen's, and others. His observations of Mars during the opposition of 1862 were employed by Stone, Winnecke, and Newcomb in fresh determinations of the sun's distance, but a fine set of measures by him of southern double stars remains unpublished. His observations, between 1849 and 1852, of all the southern stars in the 'British Association Catalogue' supplied materials for the 'Cape Catalogue for 1850,' published by Dr. Gill in 1884. The 'Cape Catalogue for 1840,' containing 2,892 stars, and the 'Cape Catalogue for 1860,' containing 1,159 stars, both published by Stone, embodied the results of Maclear's observations in 1835-40 and 1856-61 respectively. Much care was devoted by him to the collection of meteorological, magnetic, and tidal data ; and he set on foot in 1860 the communication of time-signals by electricity to Port Elizabeth and Simon's Town. Lighthouses were through his aid established in South Africa. He sat on a commission of weights and measures, promoted sanitary improvement, and contributed in innumerable ways to the welfare of the colony. African exploration interested him keenly. Livingstone was his intimate friend, and was instructed by him in the use of the sextant.

Maclear visited England, Paris, and Brussels in 1859, and was knighted in June 1860. A severe affliction befell him in the death of his wife in 1861. He retired from the observatory in 1870, and took up his abode at Grey Villa, Mowbray, near Cape Town. In 1876 he became totally blind, but was attended by a devoted family, and retained unabated interest in public matters, leaving his house for the last time to welcome Mr. H. M. Stanley at a meeting in Cape Town. He died on 14 July 1879, and was buried with his wife in the grounds of the Royal Observatory. Three days later the House of Assembly at Cape Town passed a resolution expressing their sense of his signal services to the colony. He was a member of the Astronomical Society from 1828, of the Royal Society from 1831, and was elected in 1863 a corresponding member of the Institute of France. He was besides associated with the Academy of Sciences of Palermo, and the Imperial Geographical Institution of Vienna. Maclear's life was one of unflinching devotion to science.

[Monthly Notices, xl. 200 (Gill); Proceedings Royal Society, vol. xxix. p. xviii; Nature, xx. 365; Observatory, iii. 154; Times, 6 Aug. 1879; Mémoires couronnés par l'Académie des Sciences, Bruxelles, 1873, xxiii. 77 (Mailly); André et Rayet's L'Astronomie Pratique, ii. '68; Grant's History of Astronomy, pp. 138, 149, 652; Mädler's Geschichte der Himmelskunde, Bd. ii.; information from Miss Maclear.]

A. M. C.