PHYSICA

for this cause above the rest, that they were moved by two opposite motions. One of these they attributed to the sphere moving the universe upon its poles with a motion from east to west. The other, however—and this is that which they say belongs to the other spheres which are below it, namely, the sphere of the fixed stars and the seven spheres of the planets—they assign to another oblique sphere whose poles are outside the poles of the superior sphere. And they corroborated this from the emergence of these stars in latitude from the circle called the equinoctial on this side and that.

And they said that if these stars were postponed to one another upon those equidistant circles only, then it would be manifest that they would move together, and the motion of their spheres would be upon those two poles of the sphere moving with a daily motion, and a defect of one from another would be attributed to them; and this would be from the velocity of some spheres and the slowness of others, and then it would be enough for us to say it is so. However, the motion of them to two sides, both in longitude and latitude, prevented them from this, whence they posited these two motions of the sphere declining from that first sphere, which they called the sphere of signs, and they posited its motion from the west to the east, indeed contrary to that first motion. Therefore, the cause for which they posited the sphere of signs is the declination, not the motion of longitude, for a motion of longitude would be found to be attributed to it, and it is a defect. And from this which we have said, they posited two spheres to be moved by two contrary motions, and each one of them upon two poles, and each of them to move the inferior spheres with its own motion. Therefore, the spheres in which are all the stars move, according to them, by the two motions of these spheres having contrary motion.

There is no doubt for anyone that all motion is from the moved and from the mover, as has been declared in the book of Physics. And one motion proceeds from one mover of necessity, and a simple mover moves with a simple motion, and from a simple mover do not proceed two motions, and especially contrary ones, nor is a simple motion moved by two contrary motions. Whence it follows, if the heavens were moved by these two motions, that they are to them either natural, or beyond nature, or one of them is natural and the remaining one is beyond nature; and that which is beyond nature is forced. But it is not to be said that for the heaven there is forced motion; therefore, they are natural and they have two movers. Naturally, for every natural motion proceeds from a natural mover, and it has already been declared in the book of Physics that the mover of the whole heaven is one, and the motion of the heaven is one, naturally. Therefore, in the heaven there are not two contrary motions, from the fact that its natural mover is one, and in the heaven there is only one motion, and it proceeds from one mover and to one part only.

Further, we say that it has already been declared that the heavens are simple, and it was demonstrated that the cause why the motion of them exists thus is simple; therefore, how will this simple cause move with contrary or many motions? Moreover, the forms of the parts of the heaven are uniform, and their nature is the same; why, therefore, will their parts have diverse motions? For we find among us that whatever things have similar parts, the motion of one part of them is similar to the motion of the whole, and the part is moved to where the whole is moved. For if there were a diversity in the motions of the parts of the heaven, a contrariety would follow in them; therefore, the heaven is not one, nor are its parts similar. Nevertheless, the wise man declared that they are the same and of similar parts, and there is no diversity in it; therefore, the motion of its parts is to that to which the motion of the universe is. The greatest of the parts of the heaven, however, is the sphere moving with a daily motion, and it is indeed from right to left; therefore, the motion of its parts is thither.

Further, Ptolemy said in the third treatise of the third book, in the roots supposed for mean circular motion, such words: "And we must propose universally that the motion of the sun and moon and the wandering stars in their motions, alongside the motion of the heaven—and thus the motion of the universe proceeding for all—is uniform in its nature circularly, namely, that the straight lines which are the distances of the planets from the centers of their spheres, which are imagined to revolve the planets or to be revolved with the planets..."