Astrology. To the eighth Sphere, i.e., to the starry, correspond
Natural Science, which is termed Physics, and the first Science, which
is termed Metaphysics. To the ninth Sphere corresponds Moral Science;
and to the Quiet Heaven corresponds Divine Science, which is
designated Theology.

And the reason why this is, remains briefly to be seen. I say that the
Heaven of the Moon is likened unto Grammar because it is possible to
find a comparison to it. For if you look at the Moon well, two things
are seen to be proper to it which are not seen in the other stars: the
one is the shadow which is in it, which is no other than the rarity of
its body, in which the rays of the Sun can find no end wherefrom to
strike back again as in the other parts; the other is the variation of
its brightness, which now shines on one side, and now on the other,
according as the Sun sees it. And these two properties Grammar has:
for, because of its infinity, the rays of reason can find no end in it
in parts, especially of the words; and it shines now on this side, now
on that, inasmuch as certain words, certain declensions, certain
constructions, are in use which were not formerly, and many formerly
were which again will be; as Horace says in the beginning of his book
on the art of Poetry, when he says: "Many words will spring up again
which have now fallen out of use."

And the Heaven of Mercury may be compared to Logic because of two
properties: that Mercury is the smallest star in Heaven, that the
amount of its diameter is no more than two hundred and thirty-two
miles, according as Alfergano puts it, who says that it is one
twenty-eighth part of the diameter of the Earth, which is six thousand
five hundred miles; the other property is, that it is more concealed
by the rays of the Sun than any other star. And these two properties