Anaxagoras of Clazomenae, in Ionia, was about fifteen years older than Euripides, and spent some thirty years of his life in Athens. He discovered for the first time that the moon shines by the reflection of the sun's light; and he explained, in the main correctly, the cause of eclipses. The sun was not a god: it was a white-hot mass of stone or earth, in size perfectly enormous. In describing its probable size, language failed him; he only got as far as saying--what must have seemed almost a mad exaggeration--that it was many times larger than the Peloponnese. He held, if he did not invent, a particular form of the atomic theory which has played such a great rôle in the history of modern science. He was emphatic on the indestructibility of matter. Things could be broken up into their elements and could grow together again, but nothing could be created or destroyed. There was order in the world and purpose, and this was the work of a conscious power which he called "Nous," or Mind. "All things were together in a mass, till Mind came and put order into them." Mind is outside things, not mixed with them, and some authorities say that Anaxagoras called it "God." Meantime, he showed by experiment the reality and substance of air, and disproved the common notion of "empty space." It will be seen that these ideas, if often crudely expressed, are essentially the same ideas which gave new life to modern science after the sleep of the Middle Ages. Almost every one of them is the subject of active dispute at the present day.