Sir Gerald Ponsonby Lenox-Conyngham FRS FRAS (24 August 1866 – 27 October 1956) was an Irish surveyor and geodesist. He was the last superintendent of the Great Trigonometrical Survey and began a readership in geodesy at the University of Cambridge. He was born at Springhill, Moneymore, County Londonderry, to Laura Calvert Arbuthnot, fourth daughter of Isabella Boyle and George Arbuthnot, and Sir William Fitzwilliam Lenox-Conyngham KCB DL JP, first son of Charlotte Staples and William Lenox-Conyngham. He was the seventh of eleven children. When he was aged ten, his family moved to Edinburgh, where he attended Edinburgh Academy. He went to the Royal Military Academy at Woolwich when he was seventeen years old and passed out first with the sword of honour and the Pollock medal. Attached to the Royal Engineers as a lieutenant, he spent two years at the School of Military Engineering at Chatham before being posted to India. In 1889 he joined the trigonometrical branch of the Survey of India. He became assistant to Sidney Burrard who, that same year, commenced an investigation into discrepancies evident in measurements of the longitude perpendicular to lines of latitude; the investigation provided new data which were successful. Thus began a lifelong friendship. In 1890, Lenox-Conyngham married Elsie Margaret Bradshaw, daughter of British Surgeon-General Sir Alexander Frederick Bradshaw. They had one child, a daughter named Enid (born in 1892 in India; died, unmarried, in 1993 in Cambridge, England). A redetermination of the longitude of Karachi undertaken by Burrard and Lenox-Conyngham in 1894, which required journeys to Europe and the Middle-East, was later found, using radio signals, to be accurate to 0.02 of a second of arc. In 1898, Lenox-Conyngham received two British astronomers to observe the total eclipse in northern India, including Cambridge astrophysicist Hugh Newall with whom he became firm friends, unknowingly smoothing the path for a future career at Cambridge.