by George A. Wilkins
© Oxford University Press 2004 All rights reserved
Sadler, Donald Harry (1908-1987), mathematician and astronomer, was born on 22 August 1908 at 10 St Mary's Place, Dewsbury, Yorkshire, the second son of James Wright Sadler, a master tailor, and his wife, Gertrude Jane Needham, formerly a schoolteacher. He attended the Wheelwright Grammar School in Dewsbury and won an open entrance exhibition to Trinity College, Cambridge, where he obtained first-class honours in mathematics in 1929. He spent a further year in Cambridge before joining the nautical almanac office, then based in the Royal Naval College, Greenwich, in October 1930.
Sadler became the seventh superintendent of the Nautical Almanac in July 1937, having served for a year in an acting capacity. Over the next few years he carried through successfully several projects that had been initiated by his predecessor, L. J. Comrie, including the publication in 1937 of the first British Air Almanac, for use by the Royal Air Force for astronavigation. During the Second World War the nautical almanac office was based in Bath, and additional staff were appointed to provide the computing centre of the Admiralty computing service; in addition to the navigational almanacs, Sadler planned in detail and supervised the production of many special tables and diagrams for use by the services. Of particular importance was the computation of co-ordinates for use in plotting hyperbolic lattices on charts for the newly developed top-secret DECCA navigation system, which was first used on D-day. Sadler's considerable wartime services were recognized by appointment as an OBE in 1948; he also received the Thurlow award of the American Institute of Navigation in the same year.
After the war Sadler's main efforts were first of all directed to the rationalization of the publication arrangements for the astronomical and navigational almanacs and tables that were produced by the nautical almanac office in co-operation with similar offices in other countries. He established a very good working relationship with Dr G. M. Clemence, the director of the nautical almanac office of the US Naval Observatory, and they eventually obtained agreement to the unification of the principal almanacs of the two countries. At the same time they introduced many improvements in their design. After the move of the nautical almanac office from Bath to Herstmonceaux, Sussex, in 1949 to join the Royal Greenwich Observatory, Sadler, who was one of the chief assistants to the astronomer royal, became strongly involved in the administration of the observatory.
Sadler made contributions to several astronomical and navigational organizations. He was a secretary of the Royal Astronomical Society from 1939 to 1947, and played a major role in running the society during the war; he was president in 1967-9. He participated in the formation and activities of the Royal Institute of Navigation, served as its president in 1953-5, and was awarded its gold medal in 1957. He later contributed to the formation of the International Association of the Institutes of Navigation. Sadler was strongly involved in the activities of the International Astronomical Union, firstly in scientific matters in Commission 4 (ephemerides), of which he was president from 1952 to 1958, and later in its administration; he was general secretary from 1958 to 1964 and introduced many improvements to its procedures. He represented the union on the council of the Federation of Astronomical and Geophysical Services and served as its president (1968-70). He received an honorary doctorate from the University of Heidelberg (1970) and several other foreign awards. In 1970 he gave up his day-to-day responsibility for the nautical almanac office in order to concentrate on the organization of the general assembly of the International Astronomical Union in Brighton in August. He was elected an honorary member of the American Institute of Navigation in 1979.
On 22 December 1954 Sadler had married Flora Munro McBain (1912-2000), who was a member of the staff of the nautical almanac office from 1937 to 1974; she served as a secretary of the Royal Astronomical Society from 1949 to 1954. He was a keen competitor and played a variety of outdoor and indoor games at a good standard. He retired from the Royal Greenwich Observatory in February 1972, but kept up his interests in time systems and in navigation and produced a series of papers for the Journal of Navigation. He wrote from memory a 'Personal history of HM nautical almanac office, 1931-1972' to supplement the formal record. Sadler suffered from angina, and he died at his home, 8 Collington Rise, Bexhill, Sussex, on 24 October 1987 and was cremated at Eastbourne crematorium on 2 November; he was survived by his wife.
GEORGE A. WILKINS
Sources
G. A. Wilkins, Quarterly Journal of the Royal Astronomical Society, 32 (1991), 59-65
M. W. R. [M. W. Richey], Journal of Navigation, 41 (1988), 139-41
personal knowledge (2004)
private information (2004)
Archives
CUL, papers | CUL, Royal Greenwich Observatory archives
Likenesses
H. Hardy, photograph, repro. in R. J. Tayler, ed., History of the Royal Astronomical Society, 2: 1920-1980 (1987), facing p. 98
Wealth at death
£89,251: probate, 16 Dec 1987, CGPLA Eng. & Wales
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