THEORICA

...and I found nothing except a few small motions in the words of the wise man concerning the heaven. We say, also, that this round body has two motions: one, indeed, is circular, and the other is gyratory. If the stars were to move, then without doubt they would move by one of these two motions. But if their motion were circular, then they would be fixed entirely in their places, not changing their own location at all. Yet we see them change their place, and all the ancients confessed this and held it to be true. If their motion were of this [gyratory] sort, then the motion of all stars ought to be such a motion. But now, only the sun seems to move with this motion at its rising and setting, and that it is seen thus arises not from the sun itself but because of its distance from our sight.

The wise man intended in this statement of his to notify us that the ancients said that the stars themselves have a motion in themselves, besides that by which they are moved by the spheres. But when he said that there are two motions, he alluded to two species of motions, namely, the motion of the stars through their spheres and the motion of them that is "laudable" likely referring to observable or ordered motion by the testimony of the senses, namely, the wandering stars planets and both luminaries the sun and the moon. He declared also, along with this, that the wise man believed the stars to be fixed in the locations of their spheres, having no motion except for the motion of the spheres by which they are moved. And when this is so, it is impossible for the stars to have that gyratory motion called "laudable" while they are fixed in their places in the spheres, unless from the motion occurring in the poles of the spheres to which they are fixed, with the revolution of the poles upon known circles, as we shall declare later, God willing.

And the wise man also said that the motion of the superior sphere is simple, and the motion of those that are under it are in a degree of simplicity according to their distance from it or their proximity. And from these words, it was implied—and concerning this motion and its discovery—that it is plainly visible to all that the position of the poles of the superior sphere moving the universe is different from the position of the poles of the other spheres that are under it. For if the poles of the remaining spheres were the same, then all spheres would be the same, and there would be no diversity in their motions. The motion of the spheres is upon their poles, and in this one differs from the other, although the centers of all are necessarily the same.

Ptolemy, however, who posited the poles of the sphere of signs the zodiac and the poles of the planets and fixed stars as the same, erred by a manifest error. For if the poles of all were these two poles, then they would be the same sphere, and the stars themselves would move without their spheres. But the spheres differ by the diversity of the position of their poles and by their motion upon them, and not otherwise. For the natural motion for them is upon the poles, but not upon the centers; for poles do not sustain themselves upon centers, because they are more noble than to be sustained upon them. But the motion of the spheres will necessarily be such that they are sustained upon the poles and around the center. Moreover, if they moved upon the centers, the motions of the stars existing in them would not preserve the same rectitude, and the locations of the poles would also move as other locations move besides them, and the middle of the sphere would not be more apt to be moved upon a great circle than the poles or that which is near the poles. And since it is seen in the motions of the planets that they are diverse, it follows of necessity that there is a diversity in the poles of their spheres.

Further, since motion proceeds from the first mover and from thence is its power and its source, therefore the power is stronger there; and a sign of this is the velocity of the motion. For the velocity of motion proceeds from the strength of the power, and it appears without doubt that the diurnal motion is the swiftest of all motions, and it is indeed in the most powerful sphere of all spheres, and because of this, it moves all with a diurnal motion. And he who is closer to the mover: his power is of necessity greater than the power of him who is more remote from it, and his motion is necessarily swifter. And this is by a natural merit. And he who is more distant from it is of lesser power and velocity than the first. And this is the root upon which our whole argument in this booklet is built. It appears that the swiftest of motions, whose power is most strong and indeed most simple, is the motion of the sphere moving the universe with a diurnal motion. The other spheres follow it with a motion they acquire from it, and they indeed place their intention and their end toward its motion to assimilate themselves to it, for that is their end.