(born Sept. 5 or 6, 1766, Eaglesfield, Cumberland, Eng.—died July 27, 1844, Manchester) British chemist and physicist. He spent most of his life in private teaching and research. His work on gases led him to state Dalton's law (see gas laws). He devised a system of chemical symbols, ascertained the relative weights of atoms, and arranged them into a table. His masterpiece of synthesis was the atomic theory—the theory that each element is composed of tiny, indestructible particles called atoms that are all alike and have the same atomic weight—which elevated chemistry to a quantitative science. He was also the first to describe colour blindness (1794), and his lifelong meteorological journal contains more than 200,000 observations. He is remembered as one of the fathers of modern physical science.

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