PHYSICA

...its motion will be the slower, for motion is according to the measure of virtue, and this which we say, that motion is according to the measure of virtue, is among those things which all acknowledge.

One might, however, think that all revolve with the motion of the supreme, and all orbs existing under the supreme move with a motion equal to its motion, since the universe completes a revolution in the time in which the supreme completes it, without the inferior being able to arrive at it or being delayed. Rather, one might think that the motion is the same for all, which the supreme does not surpass in any inferior one, as one imagines, placing a motion contrary to the motion of the supreme for the inferior orbs, and will say that the diurnal motion is equal for all. For the universe is continuous and united, saying that by this motion the universe will be the same and continuous, just as we see in artificial circular things existing upon the same diameter, all moving upon two poles, and one of them is below another, and they are as it were equalized in motion extrinsically and intrinsically, and there will be no excess of any of them over another in this motion.

To him it must be said that it is not so in the heaven and the motions of the heavens, so that there might be an arrangement in these bodies found among us which move upon the same axis. For the axis is that which couples them with its motion, and all move according to its motion. But if the heavens were thus, then it would follow that the earth would move, and everything that is upon it—namely, water and air—with that same motion, and the velocity would be seen more to those which are among us than to the superior ones. And if this were so, nothing would be perfectly firm and constant on the surface of the earth, nor in the air, on account of the velocity of the motion.

If, however, someone should say that circular motion is for the circular body only—namely, the orbs—and by this motion it is discerned and separated from inferior bodies, as if there were no circular motion for that which is under the heaven, but it has a direct motion by its own nature: it must be said that if the whole universe were not the same in this motion, nor continuous, but the axis coupling all were divided and its parts diverse, what will be the coupler of both motions of these two diverse parts, for which there is no virtue on account of their diversity toward each other? How, therefore, will the motion of both be the same?

Nevertheless, we say that the body of the heaven is circular. Therefore, its natural motion is upon a circle, and it is its perfection and form. And every orb desires its ultimate perfection. The supreme orb, however, moves by its own virtue and distributes it to the inferior orbs, which receive that virtue and motion, and they desire it, for it is their perfection. The inferior orbs move, however, toward the motion of the supreme by a natural motion, not forced, although it may not have been for them upon their own poles, but they follow it in the motion of the supreme as if they were carried by it, although they seek and desire it. And since they are distinct from the supreme, and to each of them there are two poles, therefore there is for the same another virtue proper to itself by which it moves toward the part of that motion coming to it from the supreme orb moving all, from the fact that that supreme distributes of that virtue to the inferiors.

Therefore, the motion by which they move from the supreme does not hinder them from their own proper motions; rather, they also move upon their own poles with a motion following this motion and joined to it, for it is not opposed to it, nor is its part contrary to its part. And since the supreme body is so separated from the virtue which it distributes to the inferior orbs as one is separated who throws a stone and an arrow—from the stone and arrow having been thrown—and is not coupled to that virtue which it distributes so that it moves the stone as long as it continues to move, but it is from the virtue extended in the arrow after the throwing of the thrower, which indeed by how much more distant it is from the mover, by so much it is weakened, so that that virtue is consumed in the fall of the arrow. Thus that virtue attributed by the supreme to the inferiors proceeds continuously diminishing until it comes to the earth, which is resting naturally. Wherefore, after its separation from the supreme to the inferiors, it does not remain in the same arrangement, but a part of that virtue is greater for that which is closer to the supreme than a part of that which is more remote, whence it is weakened at the last on account of the weakness of the virtue. Wherefore, each of the inferior orbs desires that motion of the supreme upon its own poles, for that is its perfection and form, whence it moves upon its own poles with another motion following, and extending itself toward it so that it may approach the motion of the supreme, according to Alpetragius Al-Biṭrūjī.