Conyngham, Sir Gerald Ponsonby Lenox - (1866–1956), geodesist, was born 21 August 1866 at Springhill, Moneymore, Co. Londonderry, the seventh of ten children of Sir William Fitzwilliam Lenox-Conyngham, KCB, DL, JP, and his wife, Laura Calvert, daughter of George Arbuthnot, who had lived for many years in India and founded the firm of Arbuthnot & Co. of Madras. The family moved to Edinburgh when Conyngham was nine. At the age of sixteen he left Edinburgh Academy having decided on a career in the royal engineers, and gained first place in the entrance exams. He graduated first from Woolwich, receiving the sword of honour, the Pollock medal and other prizes (1885). He then spent two years as a lieutenant at the School of Military Engineering at Chatham before he transferred to India. In 1889 he volunteered to join the trigonometrical branch of the survey of India, and thus began a passion for geodesy.
Captain Sir Sidney Burrard, in investigating longitude observations in India, chose Conyngham as his assistant and the two became lifelong friends. They redetermined the longitude of India relative to Greenwich (1894) by means of telegraph lines, with remarkable accuracy for the period. Later, in 1898–9, Conyngham began a series of observations around Kalianpur where the origin of the Indian triangulation was based. The study revealed that relative deflexions from the vertical between Kalianpur and the surrounding stations were small.
The observations of latitude that had been gathered by the survey over the previous half century showed certain correlated anomalies, and Burrard postulated that this was caused by a ‘hidden range’, in other words a subterranean rock mass, to the south of the Gangetic plain. Pendulum observations were considered the most direct method of locating such a hidden mass, through their measurement of the acceleration due to gravity. Burrard and Conyngham travelled to the Prussian Geodetic Institute in Potsdam in 1902 where they sought advice on the best pendulums to acquire. Four half-second instruments were procured and brought to Kew where they were redetermined by the National Physical Laboratory. Observations were made there and at Greenwich in order to connect the two observatories as well as to provide a base for Indian measurements. Conyngham then devoted himself and his team of over a hundred assistants to measuring thirty-nine gravity observations in India between 1903 and 1908 which were to become his greatest scientific legacy. Ironically the observations indicated a defect of mass all along the foot of the Himalayas, rather than the excess of mass which had been predicted. The instruments are kept at the Science Museum, London.
A promotion to superintendent of the trigonometrical survey in 1912 was followed by his being made colonel in 1914. He learned of his election to the Royal Society in 1918, was made a KB in 1919, and served on the council of the society in 1921–2 and 1934–6, following his return to England in 1920, when he settled at Oxford. Following his promotion of geodesy at Cambridge he was offered a position there. He moved to Cambridge in 1921 and was made a fellow of Trinity College; a readership in geodesy was created for him in 1922. Under his guidance geodetic research and teaching progressed and a thorough grounding in the discipline was given to many colonial survey officers sent to Cambridge. The school was to form part of the department of geodesy and geophysics, and Sir Edward Bullard was later (in 1931) selected as his laboratory assistant. The department expanded into further fields, such as seismology, and Conyngham was tireless in its promotion and in the procurement of funds. He also managed to acquire the support of the Royal Society, and such diverse equipment as galvanometers, ships and submarines, and his department developed into one of the most important centres of geophysical research in the world. His retirement from the praelectorship and readership took place in 1947 but he remained a fellow and continued to attend scientific gatherings as well as board meetings of a Ceylon tea company of which he was a director. On his eightieth birthday the master of Trinity described him as ‘a scholar, a soldier and a great public servant’. After a short illness he died 27 October 1956. In 1890 he married Elsie Margaret, daughter of Surgeon-General Sir Alexander Frederick Bradshaw, KCB, KHP, later head of the army medical service in India; they had one daughter.