Henry Foster, geophysicist and naval officer, was educated at Green Row, Cumberland, and entered the Royal Navy as a volunteer in 1812. He was promoted to sub-lieutenant in June 1815 and served in various ships. In 1819 he made a survey of the northern shore of the Rio de la Plata (River Plate), Uruguay. The next year he went with Captain Basil Hall* to South America, where they conducted pendulum experiments and made other observations. In 1823 he accompanied Captain Edward Sabine in the Griper to the coasts of Greenland and Norway. The following year he was promoted to lieutenant and was elected a Fellow of the Royal Society.
During 1824-1825 Foster was a member of the third expedition of Edward E. Parry in search of a North-West Passage between the Atlantic and Pacific Oceans. During this voyage he made an extensive series of geomagnetic, pendulum, and astronomical observations that were described in the Philosophical Transactions of the Royal Society of London in 1826. Among others he studied the diurnal variations of the earth's magnetic field in various places and the effect of atmospheric refraction on astronomical observations. For this work the Royal Society awarded him its Copley Medal in 1827. He was promoted to Commander the same year. Also that year he accompanied Parry in an unsuccessful attempt to ski to the North Pole.
On 12 December 1827 Foster was placed in command of the sloop Chanticleer and sent on a voyage to the South Atlantic during which he was to make pendulum observations in various places in an effort to determine the ellipticity of the earth, determine longitudes, and conduct other observations in connection with navigational astronomy. The pendulum observations were to be carried out using two of Captain Kater's invariable pendulums and two pendulums of a new design, one of iron and one of copper, supplied by the Royal Astronomical Society. He first made a series of pendulum observations at London and at Greenwich. Sailing in April 1828 he continued his observations at Montivideo (Uruguay), and Staten Island (now Isla de la Estados, near the southern tip of Argentina), the South Shetland Islands, and Cape Horn. He also carried out surveys around Cape Horn until May 1829.
Foster arrived at the Cape of Good Hope on 16 July 1829 and carried out his observations at the Royal Observatory, near Cape Town. He made 144 series of pendulum observations (out of a total of 1017 for the whole voyage), using all four his pendulums. He also made observations of the moon that were later used to determine the longitude of the Cape. After leaving the Cape on 13 December 1829 he continued his work at St Helena, Ascension Island, Fernando de Noronha Island (Brazil), Maranham (now Sao Luis, Brazil), Para (now Belem, Brazil), Trinidad, and Portobelo (Panama), where he arrived on 30 December 1830. There he also measured the difference in longitude across the isthmus, using rockets for signaling. However, he drowned while travelling down the Chagres River in a canoe on 5 February 1830.
Foster's numerous observations - the most extensive series ever made with pendulums at the time - were reduced and, with a description of his life and work as well as his instruments, published by Francis Baily in Report on the pendulum experiments made by the late Captain Henry Foster in his scientific voyage in the yearars 1828-1831, with a view to determine the figure of the earth. The report formed the whole Volume 7 of the Memoirs of the Royal Astronomical Society (London, 1834). Baily found the compression of the earth to be about 1/285 (modern value c. 1/298). Other observations were edited as an appendix to the Narrative of a voyage to the South Atlantic in the years 1828, 29, 30 (1834, 2 vols), based on the journal of W.H.B. Webster, surgeon of the Chanticleer. Foster was an accomplished and careful observer, who gave great attention to accuracy and to the smallest experimental details. However, the pendulum method to determine the shape of the earth was soon afterwards found to be defective, so that much of his work contributed little of lasting value.
