LEUCIPPUS, the founder of Atomism in Greek philosophy, flourished about the middle or latter half of the 5th century b.c. Almost nothing is known of his life. His birthplace is variously given as Elea, Abdera, or Miletus. It is disputed whether he left any writings. Empedocles of Agrigentum and Anaxagoras of Clazomenae were his contemporaries, while Zeno the Eleatic is said to have been his teacher. As pupil and associate he had Democritus of Abdera, beside whose greater fame his own work has been thrown into the background. Thus Epicurus would not look upon him as a philosopher at all; Lucretius ignored him; and he is barely mentioned by Lange, the modern historian of materialism. But the references of Aristotle, as well as of later authorities, leave no doubt that the leading principles of the Atomic theory are due to him. He eluded the Eleatic criticism of plurality and motion by postulating the reality of that which is not, the empty or space. Empty space and atoms are, he held, the ultimate constituents of all things. The former is infinite in magnitude; the latter are infinite in number, indivisible, and with only quantitative differences amongst one another. Nor is there any such thing as qualitative change; but all growth and decay are merely the compounding and separation of atoms. The atoms are always in activity or motion, and all things happen of necessity. Worlds, infinite in number, are produced by the atoms, variously shaped and of different weight, falling in empty space and giving rise to an eddying motion by their mutual impact. In this way worlds are being for ever produced and again destroyed. In the notices of Leucippus handed down to us there are additional traces of a cosmology, differing slightly from that of Democritus, and of a psychology which ...