A biography of William Wales FRS (1734-98). Wales, a mathematician and astronomer, was employed in 1765 by the Astronomer Royal Nevil Maskelyne at the Royal Observatory Greenwich as a computer, calculating ephemerides that could be used to establish the longitude of a ship, for Maskelyne's Nautical Almanac. Wales was sent by the Royal Society to observe the transit of Venus in 1769 from Hudson Bay and as a result of his work there was invited to accompany Captain James Cook on his second voyage of discovery (1772-75) on HMS Resolution, tasked with testing Larcum Kendall's K1 chronometer. He became Master of the Royal Mathematical School, was elected a Fellow of the Royal Society in 1776, and served as Secretary of the Board of Longitude (1795-98). The author has drawn on Wales's own accounts of his work and travels and provides brief details of the lives of Wales's immediate family and genealogical charts.