1766-1844

English chemist who established the modern theory of the atom. Dalton formulated the theory in order to explain chemical reactions. Although both Dalton and the ancient Greeks considered the atom (taken from the Greek word for "indivisible") the smallest part of an element, Dalton's concept of the atom was based on his studies of mixtures of gases. Studying atoms of different weights allowed Dalton to suggest a physical explanation for the law of multiple proportions. His other interests included the study of color-blindness, a condition that affected him.