of Midon, was a citizen of Athens or of Miletus; he was a pupil of Anaxagoras, who ® first brought natural philosophy from Ionia to Athens. Archelaus was the teacher of Socrates. He was called the physicist inasmuch as with him natural philosophy came to an end, as soon as Socrates had introduced ethics. It would seem that Archelaus himself also treated of ethics, for he has discussed laws and goodness and justice; Socrates took the subject from him and, having improved it to the utmost, was regarded as its inventor. Archelaus laid down that there were two causes of growth or becoming, heat and cold; that living things were produced from slime ; and that what is just and what is base depends not upon nature but upon convention. His theory is to this effect. Water is melted by heat and produces on the one hand earth in so far as by the action of fire it sinks and coheres, while on the other hand it generates air in so far as it overflows on all sides. Hence the earth is confined by the air, and the air by the circumambient fire. ‘Living things, he holds, are generated from the earth when it is heated and throws off slime of the consistency of milk to serve as a sort of nourishment, and in this same way the earth produced man. He was the first who explained the production of sound as being the concussion of the air, and the formation of the sea in hollow places as due to its filtering through the earth. He declared the sun to be the largest of the heavenly bodies and the universe to be unlimited. There have been three other men who bore the name of Archelaus: the topographer who described the countries traversed by Alexander; the author