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