Below this, again, almost in the middle region, is the sun--the leader, governor, and prince of the other luminaries; the soul of the world, which it regulates and illumines; being of such vast size that it pervades and gives light to all places.

Then follow Venus and Mercury, which attend, as it were, on the sun.

Lastly, the moon, which shines only in the reflected beams of the sun, moves in the lowest sphere of all.

Below this, if we except that gift of the Gods, the soul, which has been given by the liberality of the Gods to the human race, everything is mortal, and tends to dissolution; but above the moon all is eternal.

For the earth, which is the ninth globe, and occupies the centre, is immovable, and, being the lowest, all others gravitate towards it.
XVIII.