Now that great rivers never freeze downwards is
but consentaneous to reason. For those parts which are
frozen above transmit no exhalation outward; for this,
being penned up within and forced downward, affords
heat to the moisture at the bottom. A clear demonstration of which is this, that when the ice is dissolved, you
may observe a steam arising out of the water upwards in
a very great quantity. And therefore the bodies of living
creatures are warmest within in the winter, for that the
heat is driven inward by the ambient cold. Now those
upward exhalations and ascensions of the vapors deprive
the waters not only of their heat but of their coolness.
And therefore they that vehemently desire their drink to
be cold never move the snow nor the moisture that is
pressed out of it; for motion would deprive them both of
the virtue which is required from them.
Now that this virtue is not the virtue of air, but of water,
a man may collect by reasoning thus from the beginning.
First, it is not probable that the air, which is next the sky,
and touching the fiery substance is also touched by it,
should be endued with a contrary virtue; for otherwise it
is not possible that the extremities of the one should touch
and be contiguous to the extremities of the other. Nor is
it agreeable to reason that Nature should constitute that
which is corrupted next in order to that which corrupts, as
if she were not the author of community and harmony but
of combat and contention. For she makes use of contrary things in sustaining the universe; but she does not
use them pure and unmixed, nor so that they will be in
hostility; but she uses such as have alternately a certain
position and order which is not destructive, but which inclines them to communicate and co-operate one with another, and to effect a harmony between the opposing
qualities. And this is the nature of the air, being expanded under the fire above the water, contingent and
adhering to both, neither hot in itself nor cold, but containing an intermixture and communion of hot and cold,
harmlessly intermixed in herself; and lightly cherishing
the contrary extremities.