On The Heavens
offer any opposition. Hence a good inquirer will be one who is ready
in bringing forward the objections proper to the genus, and that he
will be when he has gained an understanding of all the differences.
Anaximenes and Anaxagoras and Democritus give the flatness of the
earth as the cause of its staying still. Thus, they say, it does not
cut, but covers like a lid, the air beneath it. This seems to be the
way of flat-shaped bodies: for even the wind can scarcely move them
because of their power of resistance. The same immobility, they say,
is produced by the flatness of the surface which the earth presents to
the air which underlies it; while the air, not having room enough to
change its place because it is underneath the earth, stays there in
a mass, like the water in the case of the water-clock. And they adduce
an amount of evidence to prove that air, when cut off and at rest, can
bear a considerable weight.
Now, first, if the shape of the earth is not flat, its flatness
cannot be the cause of its immobility. But in their own account it
is rather the size of the earth than its flatness that causes it to
remain at rest. For the reason why the air is so closely confined that
it cannot find a passage, and therefore stays where it is, is its
great amount: and this amount great because the body which isolates
it, the earth, is very large. This result, then, will follow, even
if the earth is spherical, so long as it retains its size. So far as
their arguments go, the earth will still be at rest.
In general, our quarrel with those who speak of movement in this way
cannot be confined to the parts; it concerns the whole universe. One
must decide at the outset whether bodies have a natural movement or
not, whether there is no natural but only constrained movement.
Seeing, however, that we have already decided this matter to the
best of our ability, we are entitled to treat our results as
representing fact. Bodies, we say, which have no natural movement,
have no constrained movement; and where there is no natural and no
constrained movement there will be no movement at all. This is a