That we may more easily perceive the Literal meaning of the first division, to which we now attend, it is requisite to know who and what are those who are summoned to my audience, and what is that third Heaven which I say is moved by them. And firstly I will speak of the Heaven; then I will speak of those whom I address And although with regard to the truth concerning those things it is possible to know but little, yet so much as human reason can discern gives more delight than the best known and most certain of the things judged by the sense; according to the opinion of the Philosopher in his book on Animals.
I say, then, that concerning the number of the Heavens and their site, different opinions are held by many, although the truth at last may be found. Aristotle believed, following merely the ancient foolishness of the Astrologers, that there might be only eight Heavens, of which the last one, and which contained all, might be that where the fixed stars are, that is, the eighth sphere, and that beyond it there could be no other. Again, he believed that the Heaven of the Sun might be immediate with that of the Moon, that is, second to us. And this opinion of his, so erroneous, he who wishes can see in the second book on Heaven and the World, which is in the second of the Books on Natural History. In fact, he excuses himself for this in the twelfth book of the Metaphysics, where he clearly proves himself to have followed also another opinion where he was obliged to speak of Astrology. Ptolemy, then, perceiving that the eighth sphere is moved by many movements, seeing its circle to depart from the right circle, which turns from East to West, constrained by the principles of Philosophy, which of necessity desires a Primum Mobile, a most simple one, supposed another Heaven to be outside the Heaven of the fixed stars, which might make that revolution from East to West which I say is completed in twenty-four hours nearly, that is, in twenty-three hours, fourteen parts of the fifteen of another, counting roughly. Therefore, according to him, and according to that which is held in Astrology and in Philosophy since those movements were seen, there are nine moveable Heavens; the site of which is evident and determined, according to an Art which is termed Perspective, Arithmetical and Geometrical, by which and by other sensible experiences it is visibly and reasonably seen, as in the eclipses of the Sun it appears sensibly, that the Moon is below the Sun; and as by the testimony of Aristotle, who saw with his own eyes, according to what he says in the second book on Heaven and the World, the Moon, being new, to enter below Mars, on the side not shining, and Mars to remain concealed so long that he re-appeared on the other bright side of the Moon, which was towards the West.