LIFE OF DIOGENES, OF APOLLONIA.

I. Diogenes was a native of Apollonia, and the son of Apollothemis, a natural philosopher of high reputation; and he was, as Antisthenes reports, a pupil of Anaximenes. He was also a contemporary of Anaxagoras, and Demetrius Phalereus says, in his Defence of Socrates, that he was very unpopular at Athens, and even in some danger of his life.

II. The following were his principal doctrines; that the air was an element; that the worlds were infinite, and that the vacuum also was infinite; that the air, as it was condensed, and as it was rarified, was the productive cause of the worlds; that nothing can be produced out of nothing;[130] and that nothing can be destroyed so as to become nothing; that the earth is round, firmly planted in the middle of the universe, having acquired its situation from the circumvolutions of the hot principle around it, and its consistency from the cold.

The first words of his treatise are:—

“It appears to me that he who begins any treatise ought to lay down principles about which there can be no dispute, and that his exposition of them ought to be simple and dignified.”