Now it is impossible that such prodigious movements should pass in silence; and nature teaches that the sounds which the spheres at one extremity utter must be sharp, and those on the other extremity must be grave; on which account, that highest revolution of the star-studded heaven, whose motion is more rapid, is carried on with a sharp and quick sound; whereas this of the moon, which is situated the lowest, and at the other extremity, moves with the gravest sound. For the earth, the ninth sphere, remaining motionless, abides invariably in the innermost position, occupying the central spot in the universe.