Add to these, which alone remaineth to be mentioned, the firmament of heaven, a region the farthest from our abodes, which surrounds and contains all things.

It is likewise called ether, or sky, the extreme bounds and limits of the universe, in which the stars perform their appointed courses in a most wonderful manner; among which, the sun, whose magnitude far surpasses the earth, makes his revolution round it, and by his rising and setting causes day and night; sometimes coming near towards the earth, and sometimes going from it, he every year makes two contrary reversions[165] from the extreme point of its course.

In his retreat the earth seems locked up in sadness; in his return it appears exhilarated with the heavens.

The moon, which, as mathematicians demonstrate, is bigger than half the earth, makes her revolutions through the same spaces[166] as the sun; but at one time approaching, and at another receding from, the sun, she diffuses the light which she has borrowed from him over the whole earth, and has herself also many various changes in her appearance.

When she is found under the sun, and opposite to it, the brightness of her rays is lost; but when the earth directly interposes between the moon and sun, the moon is totally eclipsed.