Ar.—No; the substance is different, and the forms are different. The term “body” is homonymously used of these bodies below and of the heavens, as has been shown by modern philosophers. All this has been demonstrated by proof. But let now the reader of this treatise hear what I have to say. Aristotle has proved that the difference of forms becomes evident by the difference of actions. Since, therefore, the motion of the elements is rectilinear, and that of the spheres circular, we infer that the substances are different. This inference is supported by Natural Science. When we further notice that substances with rectilinear motion differ in their directions, that some move upward, some downward, and that substances which move in the same direction have different velocities, we infer that their forms must be different. Thus we learn that there are four elements. In the same way we come to the conclusion that the substance of all the spheres is the same, since they all have circular motion. Their forms, however, are different, since one sphere moves from east to west, and another from west to east; and their motions have also different velocities. We can now put the following question to Aristotle: There is one substance common to all spheres; each one has its own peculiar form. Who thus determined and predisposed these spheres to receive different forms? Is there above the spheres any being capable of determining this except God? I will show the profundity and the extraordinary acumen which Aristotle displayed when this question troubled him. He strove very hard to meet this objection with arguments, which, however, were not borne out by facts. Although he does not mention this objection, it is clear from his words that he endeavours to show the nature of the spheres, as he has shown that of the things in the sublunary world. Everything is, according to him, the result of a law of Nature, and not the result of the design of a being that designs as it likes, or the determination of a being that determines as it pleases. He has not carried out the idea consistently, and it will never be done. He tries indeed to find the cause why the sphere moves from east and not from west; why some spheres move with greater velocity, others with less velocity, and he finds the cause of these differences in their different positions in reference to the uppermost sphere. He further attempts to show why there are several spheres for each of the seven planets, while there is only one sphere for the large number of fixed stars. For all this he endeavours to state the reason, so as to show that the whole order is the necessary result of the laws of Nature. He has not attained his object. For as regards the things in the sublunary world, his explanations are in accordance with facts, and the relation between cause and effect is clearly shown. It can therefore be assumed that everything is the necessary result of the motions and influences of the spheres. But when