She smiled somewhat, and then she said, "If the opinion of
mortals errs where the key of sense unlocks not, surely the
shafts of wonder ought not now to pierce thee, since thou seest
that the reason following the senses has short wings. But tell me
what thou thyself thinkest of it." And I, "That which here above
appears to us diverse, I believe is caused by rare and dense
bodies." And she, "Surely enough thou shalt see that thy belief
is submerged in error, if then listenest well to the argument
that I shall make against it. The eighth sphere[1] displays to
you many lights, which may be noted of different aspects in
quality and quantity. If rare and dense effected all this,[2] one
single virtue, more or less or equally distributed, would be in
all. Different virtues must needs be fruits of formal
principles;[3] and by thy reckoning, these, all but one, would
be destroyed. Further, if rarity were the cause of that darkness
of which you ask, either this planet would be thus deficient of
its matter through and through, or else as a body distributes the
fat and the loan, so this would interchange the leaves in its
volume. If the first were the case, it would be manifest in the
eclipses of the sun, by the shining through of the light, as when
it is poured out upon any other rare body. This is not so;
therefore we must look at the other, and if it happen that I
quash this other, thy opinion will be falsified. If it be that
this rare passes not through,[4] there needs must be a limit,
beyond which its contrary allows it not to pass further; and
thence the ray from another body is poured back, just as color
returns through a glass which hides lead behind itself. Now thou
wilt say that the ray shows itself dimmer there than in the other
parts, by being there reflected from further back. From this