DALTON, JOHN. — Chemist, born in Eaglestfeld (Cumberland) on 6 September 1766, died in Manchester on 27 July 1844. Coming from a poor family, he earned his living by giving lessons as an elementary-school teacher; he studied mathematics and physics on his own; he never held public or prominent positions: his life was characterized by great modesty and a lively passion for study; one of his biographers says that “he was a model of virtue without ostentation and of religion without fanaticism.”
He is to be regarded as the founder of modern atomic theory on an experimental basis: to him is owed the law of multiple proportions (1802–1808; V. CHIMICA), and to his influence, Proust’s law of constant proportions (1799–1806). The genesis of his ideas is to be found in the studies of his friend Henry (1744–1836) on the influence of pressure on the solubility of gases in liquids. The work to which he entrusted the exposition of his doctrine is New System of chemical philosophy (3 vols., Manchester 1808, 1810, and 1827); while its diffusion, besides being due to its truth and fruitfulness, was owed to the eloquent manner in which it was disseminated by his friend T. Thomson (1773–1852).