Defying his father’s wish that he become a clergyman, Maclear studied medicine at Guy’s and St. Thomas’s hospitals in London. In 1815 he joined the staff of Bedford Infirmary, where his interest in astronomy was aroused by his friendship with Admiral William Henry Smyth. From 1823 he practiced medicine in Biggleswade, Bedfordshire, where he set up a small observatory in his garden; he was lent the Wollaston telescope by the Royal Astronomical Society to observe occupations of Aldeharan which he had himself calculated. In 1833 he was appointed Her Majesty’s astronomer at the Cape of Good Hope, where he arrived on 5 January 1834, shortly before John Herschel.
Until his retirement, Maclear devoted himself to the work of the observatory and to matters of public welfare in the colony. From 1837 to 1847 he carried out the remeasurement and extension of Lacaille’s arc as a basis for the survey of the colony, and this earned him the Lalande Prize in 1867 and a Royal Medal in 1869. In 1839–1840 and 1842–1848 he observed a Centauri to confirm the parallax derived by Thomas Henderson. He made numerous obser-vaiions of comets and double stars, and furnished materials for successive Cape Catalogues. His observations of Mars during the opposition of 1862 were used by others in determinations of the sun’s distance.
Maclear also promoted a wide range of applied sciences in the colony. He assembled meteorological, magnetic, and tidal data, and in 1860 he established time signals for Port Elizabeth and Simonstown. He sponsored the construction of lighthouses, promoted sanitary improvements, and took part in a commission on weights and measures. He was keenly interested in African exploration and was a friend of Livingstone and Stanley.
Maclear was knighted in 1860. He retired in 1870 and went blind in 1876, but he continued to interest himself in public affairs at the Cape until his death.
I. Original Works. Maclear’s writings include The Verification and Extension of Lacailte’s Are of the Meridian at the Cape of Good Hope, 2 vols. (London, 1866), and numerous papers, mostly in the Memoirs and Monthly Notices of the Royal Astronomical Society. Lists of these papers are given in the Royal Society Catalogue of Scientific Papers, IV (1870), 166–168, and VIII (1879), 299–300; and in Poggendorff, III, 852–853.
II. Secondary Literature. The most important memoir on Maclear’s astronomical work at the Cape is ch, 7, “Les travaux de Maclear au cap de Bonne-Espérance,“of “Tableau de I’astronomie dans l’hémisphère austral et dans rinde,“by É. Mailly, in Mémoires courotmés et mémoires publicés par l’Académie royafc des sciences, des letters et des beaux-arts de Belgiqae,23 (1873), 77–109. Extensive biographical sketches are by David Gill in Monthly Notices of the Royal Astronomical Society,40 (1880), 200–204, and by Agnes M. Clerke in Dictionary of National Biography, XII, 648-649.
Michael A. Hoskin
"Maclear, Thomas." Complete Dictionary of Scientific Biography. . Encyclopedia.com. (January 22, 2019). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/maclear-thomas
"Maclear, Thomas." Complete Dictionary of Scientific Biography. . Retrieved January 22, 2019 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/maclear-thomas