John Dalton was a chemist and meteorologist whose genius revived and modernized the ancient idea of the atom. In 1803, he proposed that all matter is composed of tiny, indivisible particles called atoms, and that atoms of a given element are identical in mass and properties. This 'Dalton's Atomic Theory' provided a physical basis for how chemical reactions occur—by the rearrangement of atoms in fixed ratios. He also formulated the Law of Partial Pressures in meteorology. Dalton was also the first to scientifically describe color blindness (which he suffered from), a condition still occasionally referred to as 'Daltonism' in some languages.