John Dalton

Dalton was an English chemist, physicist, and meteorologist born in early September 1766. For over fifty years he kept daily weather records, and his work on gas behavior led him to formulate the first empirical law of partial pressures. Studying his own vision, he produced the first scientific account of color blindness - a condition still called Daltonism in several languages. Then in 1808 he published A New System of Chemical Philosophy, proposing that elements consist of identical atoms of characteristic weight and that compounds form when those atoms combine in fixed proportions. The book supplied relative atomic weights, symbolic notation, and a quantitative foundation that moved chemistry from guesswork to mathematics. Elected to the Royal Society in 1822 and awarded its Royal Medal four years later, Dalton became the first British scientist to build a working atomic theory. He died in July 1844; today a unit of atomic mass bears his name.