Page:Early Greek philosophy by John Burnet, 3rd edition, 1920.djvu/253

Rh It had just been discovered that the moon shone by reflected light, and there is always a tendency to give any novel theory a wider application than it really admits of. In the early part of the fifth century B.C., men saw reflected light everywhere; some of the Pythagoreans held a similar view (§ 150).

It was probably in this connexion that Empedokles announced that light takes some time to travel, though its speed is so great as to escape our perception.

"The moon was composed of air cut off by the fire; it was frozen just like hail, and had its light from the sun." It is, in other words, a disc of frozen air, of the same substance as the solid sky which surrounds the heavens. Diogenes says that Empedokles taught it was smaller than the sun, and Aetios tells us it was only half as distant from the earth.

Empedokles did not explain the fixed stars by reflected light, nor even the planets. They were made out of the fire which the air carried with it when forced beneath the earth by the upward rush of fire at the first separation. The fixed stars were attached to the frozen air; the planets moved freely.

Empedokles was acquainted (fr. 42) with the true theory of solar eclipses, which, along with that of the moon's light, was the great discovery of this period. He also knew (fr. 48) that night is the conical shadow of the earth, and not a sort of exhalation.

Wind was explained from the opposite motions of the fiery and airy hemispheres. Rain was caused by the compression of the Air, which forced any water there might be in it out of its pores in the form of drops. Lightning was fire forced out from the clouds in much the same way.