Dalton, John (1766–1844), English scientist who originated the modern chemical atomic theory. In 1801 Dalton discovered his Law of Partial Pressures, which states that the pressure exerted by a mixture of gases equals the sum of the partial pressures of the components. (The partial pressure of a gas is the pressure it would exert if it alone filled the volume.) In 1803 he published the first table of comparative atomic weights, which inaugurated the new quantitative atomic theory. Dalton also gave the first scientific description of color blindness. The red-green type from which he suffered is still known as Daltonism.
See also: Atom.