=The Philosophy of the Atomists――Leucippus and the School at Abdera.= Only circumstantial evidence is left to testify to the early beginnings of the school of atomists at Abdera. About 450 B. C., owing to the rise of Athens and the great victory of Cimon over the Persians, the Ionian civilization on the coasts of Asia Minor had a new lease of life, and there was a renewal of scientific activity in the cities. The influence of the Milesians appeared and Anaxagoras’ doctrine, which had been widely disseminated, began to have great vigor. Among the philosophers of this section was one about whom we know very little, except that his name was Leucippus and that he was the father of atomism. Miletus was probably his native place, and after visiting Elea he settled in Abdera in Thrace. We know that the polemic of Zeno was directed against contemporary atomism; and we know the theories of the pupils of Leucippus, of Protagoras, and of Democritus, in whom the doctrine of atomism culminated. Probably the theory of Leucippus was that the cosmic substance is composed of _an infinite number of elements quantitatively distinct_, in opposition to Empedocles’ theory of a fourfold division as well as against Anaxagoras’ theory of an infinite number of qualities. Atomism in this early form represents one of the ways that Greek thought took in reconciling the conflicting claims of Heracleitus and Parmenides. The doctrine of atomism will be presented fully in its greatest representative, Democritus.