An English scientist and millionaire grandson of the Duke of Devonshire, he devoted his life to scientific investigation. A skilled experimenter, the drawing-room of one of his three London houses was a laboratory, with a forge in the next room and an observatory upstairs. He invented many new methods in both chemistry and physics. He determined many specific heats, the freezing point of mercury, and the relative density of gases. He also discovered the dielectric constant and ‘weighed (p. 58) the Earth’. He was the first to investigate hydrogen, to synthesize water (which until then was thought to be an element), and to analyse air. In 1785 he made nitric acid by sparking nitrogen with oxygen. He also refined many methods such as drying gases for the correction of gas volumes for temperature and pressure. The French scientist Jean-Baptiste Biot (1774–1862) said that he was: ‘le plus riche de tous les savants, et probablement aussi le plus savant de tous les riches’. The Cavendish Laboratory in Cambridge is his national memorial and contains much of his apparatus.