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
are in Logic: for Logic is less in substance than any other Science,
for it is perfectly compiled and terminated in so much text as is
found in the old Art and the new; and it is more concealed than any
other Science, inasmuch as it proceeds with more sophistical and
probable arguments than any other.

And the Heaven of Venus may be compared to Rhetoric because of two
properties: the one is the brightness of its aspect, which is most
sweet to behold, far more than any other star; the other is its
appearance, now in the morning, now in the evening. And these two
properties are in Rhetoric: for Rhetoric is the sweetest of all
Sciences, since it principally aims at sweetness. It appears in the
morning, when the Rhetorician speaks before the face of the hearer; it
appears in the evening, that is, afterwards, when it speaks by Letters
in distant parts.

And the Heaven of the Sun may be compared to Arithmetic because of two
properties: the one is, that with his light all the other stars are
informed; the other is that the eye cannot gaze at it. And these two
properties are in Arithmetic, which with its light illuminates all its
Sciences: for their subjects are all considered under some Number, and
with Number one always proceeds in the consideration of these; as in
Natural Science the movable body is th