born 460 died 370 BC Greek philosopher. Though only a few fragments of his work survive, he was apparently the first to describe invisible "atoms" as the basis of all matter. His atoms indestructible, indivisible, incompressible, uniform, and differing only in size, shape, and motion anticipated with surprising accuracy those discovered by 20th-century scientists. For his amusement at human foibles, he has been called "the Laughing Philosopher." See also atomism
{i} ancient Greek scientist and philosopher, precursor of the atomic theory (ca. 400 B.C.)