Gerald Lenox Conyngham

Sir Gerald Ponsonby Lenox-Conyngham (21 August 1866 – 27 October 1956) was an Irish surveyor and geodesist. He was the last superintendent of the Great Trigonometrical Survey from 1912 to 1921, and was reader in geodesy at the University of Cambridge from 1922 to 1947.

Early life and family 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. 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 on 16 September 1885, he spent two years at the School of Military Engineering at Chatham before being posted to India.

Career 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. 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. He was promoted to major on 17 January 1903, while he was posted to Dehradun.

Burrard suggested that anomalies in latitude found by the Survey in the early 1800s parallel to the mountains to the north might be caused by a large mass below the Indo-Gangetic Plain. New four-pendulum-based equipment to measure the gravitational force was modified to suit and, between 1903 and 1908, Lenox-Conyngham collected gravitational data across the subcontinent. The data showed a negative relative gravitational component in the region of the Plain, a fact readily apparent in modern measurements (see image). He added seismology and geothermal science to his curriculum and worked hard to secure funds and equipment. He made an expedition to the Great Barrier Reef (regarding the isostasy of Pacific islands), and was asked to visit Montserrat to investigate earthquakes. He attended conferences worldwide and even acted as a representative of the British government in the Pacific Science congresses of 1923 and 1926. His faculty later became the Department of Geodesy and Geophysics (incorporated in 1980 into the Department of Earth Sciences). His students included pioneering scientists such as the geophysicist Edward Bullard.

He retired in 1947. He died at Addenbrooke Hospital aged 90 and his funeral service was at Trinity College Chapel. He is commemorated there by a brass plaque with a Latin inscription on the south wall of the Ante-Chapel. The translation includes: "He approved innovative ideas but also old-fashioned values. A kind, prudent, dutiful man".