PHYSICS

...that which is found in this inferior world from great mutations and the permutation of particular things, such as the permutation of inhabited to uninhabited and mediocre to non-mediocre. And sometimes the air is corrected in some direct places, and thus habitations are made in them, and the air is corrupted in some places, and they are destroyed, and thus the waters of the sea are changed and predominate in some places, and places previously covered by waters appear. For that which appears from these things and the like testifies that these operations proceed from the permutation of its situation. And they are not perfectly because of any of the spheres of the planets, for if they were the cause of any of them, then they would be doubled and would return with its doubled motions, and would return to its reversion. Therefore, they are the cause of the orb of the fixed stars.

This sphere is called the orb of the fixed stars from the constancy of the distance of the stars existing in it from one another. And its diurnal motion proceeds necessarily from another sphere moving it, absolutely most simple, whose poles are other than the poles of the orb of fixed stars. The motion of the orb of fixed stars upon its own poles is, however, its motion of itself. But yet the orb of fixed stars is not in the ultimate state of simplicity; composition, indeed, appears in it. For the stars affixed to it and the milky places, although they are all of the same material, are nevertheless diverse from others in light and splendor. For if they were all the same, they would be entirely the same, and one part of it would not be diverse from another in any way. And thus other spheres differ from one another by the plurality of motions and the diversity of poles and the stars affixed to them and their accidents, namely the ways of the transmission of light; for some are illustrious from themselves, and some acquire light from others. Furthermore, the light of the fixed stars and the planets is diverse. For some appear with the color of wax, and some with the color of fire, and some as if they were burning, and some whitish, and some obscure, as is seen of them by sense; nor does distance and proximity, nor thick and thin air, make that, but they always hold themselves thus with the diversity of the disposition of the air, and they do not change except by certain mutations which are from the cause intermediate between them and our sight, and the purity and turbidity of the air. Which things, even if they be accidents to these substances, are nevertheless properties of each one for their consistency, and they are as it were differences and substances to them. The substance of the whole heaven, even if it were the same, will nevertheless be the same in some way and not the same in every way, for from it is that which is of perfect simplicity, and from it is that which is not of perfect simplicity, and its parts differ in this according to more and less.

And when it has been confirmed that the motion of the orb of the fixed stars is not simple, and its parts differ from one another, therefore it is not in the ultimate state of simplicity, and another [sphere] besides it is in the state of perfect simplicity. And when it is of perfect simplicity, it is impossible for it to be apprehended by sense; for the senses do not apprehend anything except accidents, but it itself does not have an accident. Therefore, it is remote from apprehension except by the intellect. Wherefore it becomes manifest through the motion found in the universe; nor is its motion a testimony, but the testimony of this is the motion of the bodies which move according to its motion and not otherwise, and from them it is also proven that if there is motion and a mover, then it is apprehended by the intellect. And perhaps it is that which is called in the Alcoranus Quran by the name "Throne," when it said: "The breadth of His throne is the heaven and the earth," and perhaps it is that which is called "bed," when it said: "God, there is no God but He, the Lord of the excellent bed." And perhaps one of them is the orb of fixed stars, and the other is the first mover of the universe, and this is what led us to say that this ninth sphere exists. The eighth, however, is hinted at by him when he said: "We have adorned the lower heaven with stars," and he does not, of course, understand by "lower" an inferiority with respect to the earth, but with respect to the highest, and it is truly inferior to the first mover. And this is what led us to reject other spheres besides the seven posited in the noble book; that is, to reject those eccentric spheres and epicycles, of which there is a great number among them who posited them from the ancients of this science. Therefore, the highest simple sphere is that which moves from itself and is the mover of all existing under it and does not receive motion from another body, and all the spheres which are under it move according to its motion, and each fulfills its intention.