When God created the firmament He ordained a full perfect motion that never increases or decreases; since in twenty-four hours the firmament completes its course without fail and without deception, and those twenty-four hours are day and night.
God also made the sphere of the sun to manifest day and night and their nature, their length, and shortness, and to manifest the regularity of the heavens, and the difference of increase and decrease of heat and cold in different places, in order to propagate creatures from each other, and to fulfil the order of the world, because if the firmament and the sun moved more quickly than they do, the days and nights would be shortened, the sun would not have time to fulfil its functions, and terrestrial creatures would refuse to grow; and if they moved more slowly than they do, night and day would be lengthened, and, consequently, as the sun would be too long over the earth, it would parch and dry up the surface of the earth, and would permit nothing to grow in the soil. Thus men could not dwell in the southern part of the world, as they do now, at a distance of sixteen degrees
I mentioned above that there are none of the opposite qualities in the firmament from which every corruption and dissolution results, and consequently they have no opposite motion, since the motion of every body in the universe must be circular or vertical or a compound of both as is the motion of a cart (wheel ?). The circular and vertical motions are simple, consequently every body, simple or compound, moves in a circle or vertically. But circular motion is the motion that moves like a circle around a centre, and vertical motion is the motion that moves from a centre upwards (?) or to a centre downwards, and the three motions are simple motions, and the circular motion is simpler than the other two motions, because the body that moves thus is simpler than any other body.
Those two motions that move to and from the centre are compound compared to the circular motion, and they
Additional proof of the same thing: the philosophers declare that the motion that is foreign to one thing is natural to another, for instance the upward motion of fire and of earth, or the downward motion of both. As every non-essential thing is accidental, and every essential natural thing is a substance, and as the accident and the substance are opposite to each other in the same way the non-essential motion and the natural motion are opposite to each other. Not only (that), but things that are below and above, right and left, before and behind, are contrary to one another. And as everything which has not contrariety is nobler than that which has, in the same way the circular motion which has no contrariety is superior to every other motion I have mentioned.
Additional proof of the same thing: everything that moves naturally with a vertical motion can be moved
Although each of the spheres of the firmament has a separate motion, they all move together without opposition; for, if there were contrariety in the firmament as there is in the elemental bodies, everything it effects in them would cause a similar effect in the firmament, and thus the strongest body in the firmament would change the weakest body into its own nature, and similarly we should see the planets, and constellations, and the other stars at one time larger, at another smaller than one another. This is not seen now, and was not, and never will be seen. Thus it is clear whence those changes, i.e., the contrariety in the firmament can be understood.
Thus is the great smooth, firm body in the firmament—a round sphere like a ball, around its own centre, with its centre in a middle point, which remains for ever in one point, and ever moving; and it is certain that the motion is uniform since it has never made the least halt, and does not move swifter or slower at one time more than another, and thus are the seven spheres of the seven planets:—Luna, Mercury, Venus, Sol, Mars, Jupiter, Saturn, and the sphere of the fixed stars and the sphere of the twelve signs, i.e., the sphere which we call the firmament. Thus were those ten spheres since the time God created them, and thus will they be for ever, as long as He wishes them to be thus.
The uninformed say that the primary properties of the elements, and the properties of the things that are compounded of them, are contained in the twelve signs and in the planets, and they declare that Aries, Leo, and Sagittarius are warm and dry in accordance with the nature of fire; and Taurus, Virgo, and Capricornus cold and dry of the nature of earth; Gemini, Libra, and Aquarius warm and wet of the nature of air; Cancer, Scorpio, Pisces cold and wet according to the nature of water. And they say that some of those signs are movable, and some firm and immovable, and some neutral. They say also that some of them are male and some female, some light and some dark, and they say that some of the planets are good and some bad, and that some of them are favourable and auspicious for good people, and others unfavourable, adverse, and inauspicious for bad people. They say again, if the sun were not hot in its own substance, it would not perform the functions of heat which we see in terrestrial things, for it performs the very same functions in terrestrial things as does fire (which is hot in its own substance), namely, burning, parching and charring.
They say again, that if the moon were not wet in itself it would not produce wetness in terrestrial things. Against this I declare that that theory is scientifically incorrect and false; and I declare that the signs of the firmament are neither wet, nor hot, nor cold, nor good, nor bad; although it is from their union (together) and from their motion that they produce those properties; although (in themselves) they are not present in terrestrial things, because they were all made from one substance and one material; and I will explain this in more detail afterwards.