the moving bodies are all of them of a small size, because they so
to us, looking at them from the earth.
This a matter which we have already discussed in our treatment of
the upper region, but we may return to the point now.
If the intervals were full of fire and the bodies consisted of
fire every one of the other elements would long ago have vanished.
However, they cannot simply be said to be full of air either; for
even if there were two elements to fill the space between the earth
and the heavens, the air would far exceed the quantitu required to
maintain its proper proportion to the other elements. For the bulk
of the earth (which includes the whole volume of water) is
infinitesimal in comparison with the whole world that surrounds it.
Now we find that the excess in volume is not proportionately great
where water dissolves into air or air into fire. Whereas the
proportion between any given small quantity of water and the air
that is generated from it ought to hold good between the total
amount of air and the total amount of water. Nor does it make any
difference if any one denies that the elements originate from one
another, but asserts that they are equal in power. For on this view it
is certain amounts of each that are equal in power, just as would be
the case if they actually originated from one another.
So it is clear that neither air nor fire alone fills the
It remains to explain, after a preliminary discussion of
difficulties, the relation of the two elements air and fire to the
position of the first element, and the reason why the stars in the
upper region impart heat to the earth and its neighbourhood. Let us
first treat of the air, as we proposed, and then go on to these
Since water is generated from air, and air from water, why are
clouds not formed in the upper air? They ought to form there the more,
the further from the earth and the colder that region is. For it is