The Principle of Motion

The whole in a certain respect always remains and rests and yet is continually moved but this happens reciprocally. Because circulation is the measure of motions it is necessary that it should be the first motion for all things are measured by that which is first. A circular motion alone can be equable since each is similarly beginning middle and end so that some things are always and never in the beginning and end hence a sphere in a certainrespect is moved and is at rest.