Meteorology   

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

intermediate space.

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

questions.

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