All scholars who have attended to the history of Greek speculation know that the Greeks held to the belief in polytheistic personal agents as the active producers of the phenomena of Nature. This was the system of Homer and Hesiod and the other old poets. This was the popular belief held throughout all the Hellenic world, and it continued to be the faith of the general public, not only after the different schools of philosophy had arisen, but down to and after the time when St. Paul stood on Mars Hill and told the men of Athens how he had found that they were in all things too superstitious. Thales, who flourished in the first half of the sixth century before Christ, was the first Greek who suggested a physical agency in place of a personal. He assumed the material substance, water, to be the primordial matter and universal substratum of everything in Nature. All other substances were, by transmutations, generated from water, and when destroyed they all returned into water. His idea of the earth was that it was a flat, round surface floating on the immense watery expanse or ocean. In this he agreed with the old poets; but he did not, like them, suppose that the earth extended down to the depths of Tartarus. The Thalesian hypothesis, therefore, rejected the Homeric Okeanus, the father of all things, and substituted for that personal agency the agency of one primordial physical substance, by its own energy producing all other substances. This is about all that is known of the philosophy of Thales, and even this is not known from any extant writing of his, but it is derived from what subsequent writers, including Aristotle, have imputed to him.[4] Why Lord Macaulay should have selected Thales as the Greek philosopher who was as favorably situated as a philosopher of the present day for dealing with questions of natural religion, is not very apparent. All that Thales did, assuming that we know what he did, was to strike out a new vein of thought, the direct opposite of the poetical and popular idea of the origin of phenomena.