Generally speaking, the value of the Leucippic theory has only been recognised since the Renaissance. For although Democritus of Abdera extended his master’s admirable system to fresh departments of knowledge, established it more firmly by combating the sensualism of Protagoras and other theories arising from a misunderstanding of Leucippus, and, above all, brought it to a high pitch of mathematical and notional exactitude, yet the atomistic school which continued to exist at Abdera till into the fourth century has passed almost utterly out of mind. Plato ignored it, although he adopted many of its theories indirectly; Aristotle alone made use of it, though not as regards the main points of its teachings; and Epicurus, who borrowed from it almost the whole of his theoretical science, by this very absorption played the chief part in the destruction of the Abderite writings, the greatest loss that science has ever suffered. How can we explain this astounding disregard of atomistic philosophy? In some degree by the fact that Leucippus settled in the barbarous north, far away from Athens, which had grown since the Persian wars to be more and more the _prytaneion_, or central focus of warmth to Hellas, and drew all talent to itself from every quarter; and further, from the fact that the natural science which was dominant in the sixth century and the beginning of the fifth--and was regarded, indeed, as the only legitimate kind of scientific thought--lost its hold on men’s minds towards the middle of the fifth century. We have evidence of this in Eleatism, which, with Zeno and Melissus, devoted itself to purely dialectical questions and abandoned the interpretation of nature. We have evidence of it, again, in Empedocles, who in his second series of didactic poems (_Katharmoi_) flings himself into the arms of Orphic mysticism; and in his pupil, Gorgias, who proceeded from physics to nihilism and thence to mere superficial rhetoric. We have the strongest proof of all in Democritus himself, who embraced inductive logic, æsthetics, grammar, and ethics within the range of his studies as well as the old questions of physics. Thus during the Peloponnesian War the way was prepared for the new epoch which was performed with Athens for a stage, and Socrates, Plato, and Aristotle for heroes. II