THEORICA Theory

...two other diversities from the declination of the epicycle a small circle whose center moves around the circumference of a larger one which they assign to it. And thus they constituted for the wandering planets such motions in longitude and latitude and declination, and they are with this diverse in velocity and slowness, and with this they have also sometimes a station and sometimes a retrograde backward motion and sometimes a direction with declination and in latitude. And this declination is sometimes diversified in them, and the motion in latitude in Venus and Mercury will be diverse according to the declination of the epicycle, just as it happens to the moon; indeed, the motion of their two carrying orbs deferents of the center of the epicycle will be always to the north in Venus and always to the south in Mercury, for the planet in the part where it is traverses and reaches the contrary part, and it has already reached that part. And Venus has traversed the southern part of the zodiac when it has reached the point of intersection, and it has already become northern, and Mercury has traversed and reached the northern part at the point of intersection, and it has already become southern; thus the planet will be from this in one part of the zodiac. And such motion is indeed impossible to imagine in the heaven, for it is not circular in truth. And all these motions indeed happen because they have them from observation and because they show themselves to sight, and the diversity of these motions toward one another compelled Ptolemy to posit these roots near those positions, so that he might constitute the theory of those motions.

And when he had established the measures of these motions, he said, from that which seems to him concerning the motion of the orb of the fixed stars, as his observation and the observation of his predecessors attribute to it, that it moves indeed contrary to the motion of the universe and according to the order of the signs the zodiac and upon the poles of the orb of the signs, one degree every hundred years, and it completes one revolution for the return to the place from which it departed in 36,000 solar years. And his successor, the doctor Alzarcala al-Zarqali/Arzachel, opined in his booklet on the motion of approach and recession that this motion is not as Ptolemy thought, always according to the order of the signs. And it was affirmed by him from the observations of Ptolemy, saying that it is according to the order of the signs, and from the observation of predecessors and likewise from his own observations, that the motion is sometimes proceeding according to the order of the signs and sometimes postponing toward the part of the motion of the universe and contrary to the order of the signs. And he supposed for this motion certain positions and roots, just as the roots of Ptolemy posited for the planets, or many of them, far from the truth. Therefore, all those roots are indeed imaginary, although they are circles moving and moved, and they are not true roots to which one should adhere. Although that which Alzarcala said concerning the approach and recession of this orb has already been mentioned before, and it has been written about this motion in the tables of those exercising themselves in this science, but since the motion was imaginary and not true nor precise, therefore the later ones were silent about it, and from their silence, a controversy arose concerning the places of the fixed stars.

And it has already been established that the orb of the fixed stars has another motion besides the diurnal motion, and this has been apprehended by sense and observation from the truth of the translation of the stars existing in it; and so also in other orbs there are motions by which they are distinguished from one another. And they are not indeed motions of the orbs except by the differences of their poles and the position of some against the position of others. And the position of the poles of all these orbs is a distinct position, and this indeed appears from the translation of the stars posited in them, for the wise man has declared that they are affixed to their orbs, bound to them by no mediocre bond, and that they never move except to the motion of the orbs. And it has been verified from their observation that for individual planets there are translations, some indeed in longitude and some in latitude, differing by more and less, namely that for certain planets there are mutations which are not for the others, according to the composition of their orbs and the remoteness from the mover and proximity. And it is manifest necessarily that all these orbs are of the same disposition as to the circumference, and they are contiguous to one another, and there is no distance between them, nor an extraneous body, nor any diversity between them except in the position of the poles and their motion upon them only. And it is clear also by itself that their motions are not from the center...