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is colder in the middle more than it is anywhere else.
You see this -- you can always see this -- with mountains that are in
high places, like the mountains of Savoy and Piedmont, and
in other high mountains where there is
habitually more snow than in the plain. All of this
occurs because of the coldness of the air, which
contains less heat higher up than it does lower down,
since it is thinner than the air that is below.
And the thinner it is above, the less it retains
heat, but the thicker the air is the more it heats up
quickly when then sun comes. One can see the same effect
when iron and steel heat up quicker in the sun than stone does.
For the harder and thicker a thing is by nature, the more
fiercely and quickly it takes flame, compared to those things
which have less strength. And I tell you also
about the air that is above us, that it is colder than
the air here below because it is not as thick as the
air that is near the earth, and because of the
wind that is often engendered there and that it causes