Dalton, John (1766–1844)

English chemist who proposed the theory of atoms, which he considered to be the smallest parts of matter. He produced the first list of relative atomic masses in ‘Absorption of Gases’ in 1805 and put forward the law of partial pressures of gases (Dalton's law).

Dalton was born near Cockermouth in Cumbria. As a Quaker, he was precluded from attending Oxford or Cambridge (then open only to members of the Church of England), and was self-taught. For 57 years he kept a diary of observations about the weather, and this led to his interest in gases. He was one of the first scientists to note and record colour blindness (he was himself colour blind).

Dalton set out his atomic theory in New System of Chemical Philosophy 1808. The chemical symbols he introduced would soon be superseded by the system created by Swedish chemist Jöns Berzelius.