following objection: There are spheres below the eighth that move from east to west. Of these each upper one, according to this rule, would have a greater velocity than the lower one; and the velocity of these spheres would almost equal that of the ninth sphere. But Astronomy had, in the days of Aristotle, not yet developed to the height it has reached at present. According to our theory of the Creation, all this can easily be explained; for we say that there is a being that determines the direction and the velocity of the motion of each sphere; but we do not know the reason why the wisdom of that being gave to each sphere its peculiar property. If Aristotle had been able to state the cause of the difference in the motion of the spheres, and show that it corresponded as he thought to their relative positions, this would have been excellent, and the variety in their motions would be explained in the same way as the variety of the elements, by their relative position between the centre and the surface; but this is not the case, as I said before. There is a phenomenon in the spheres which more clearly shows the existence of voluntary determination; it cannot be explained otherwise than by assuming that some being designed it: this phenomenon is the existence of the stars. The fact that the sphere is constantly in motion, while the stars remain stationary, indicates that the substance of the stars is different from that of the spheres. Abu-nasr has already mentioned the fact in his additions to the Physics of Aristotle. He says: “There is a difference between the stars and the spheres; for the spheres are transparent, the stars are opaque; and the cause of this is that there is a difference, however small it may be, between their substances and forms.” So far Abu-nasr. But I do not say that there is a small difference, but a very great difference; because I do not infer it from the transparency of the spheres, but from their motions. I am convinced that there are three different kinds of substance, with three different forms, namely:—(1) Bodies which never move of their own accord; such are the bodies of the stars; (2) bodies which always move, such are the bodies of the spheres; (3) bodies which both move and rest, such are the elements. Now, I ask, what has united these two bodies, which, according to my opinion, differ very much from each other, though, according to Abu-nasr, only a little? Who has prepared the bodies for this union? In short, it would be strange that, without the existence of design, one of two different bodies should be joined to the other in such a manner that it is fixed to it in a certain place but does not combine with it. It is still more difficult to explain the existence of the numerous stars in the eighth sphere; they are all spherical; some of them are large, some small; here we notice two stars apparently distant from each other one cubit; there a group of ten close together; whilst in another place there is a large