a pathway up and down, and this determines the birth of the world. For fire by contracting turns into moisture, and this condensing turns into water ; water again when congealed turns into earth. This process he calls the downward path. Then again earth is liquefied, and thus gives rise to water, and from water the rest of the series is derived. He reduces nearly everything to exhalation from the sea. This process is the upward path. Exhalations arise from earth as w r ell as from sea ; those from sea are bright and pure, those from earth dark. Fire is fed by the bright exhalations, the moist element by the others. He does not make clear the nature of the surrounding element. He says, however, that there are in it bowls with their concavities turned towards us, in which the bright exhalations collect and produce flames. These are the stars. The flame of the sun is the brightest and the hottest ; the other stars are further from the earth and for that reason give it less light and heat. The moon, which is nearer to the earth, traverses a region which is not pure. The sun, however, moves in a clear and untroubled region, and keeps a proportionate distance from us. That is why it gives us more heat and light. Eclipses of the sun and moon occur when the bowls are turned upwards ; the monthly phases of the moon are due to the bowl turning round in its place little by little. Day and night, months, seasons and years, rains and winds and other similar phenomena are accounted for by the various exhalations. Thus the bright exhalation, set aflame in the hollow orb of the sun, produces day, the opposite exhalation when it has