The Complete Aristotle (eng.)

does D, and the time G will be twice the
time E. And always, by so much as the medium is more incorporeal
and less resistant and more easily divided, the faster will be the
movement.
    Now there is no ratio in which the void is exceeded by body, as
there is no ratio of 0 to a number. For if 4 exceeds 3 by 1, and 2
by more than 1, and 1 by still more than it exceeds 2, still there
is no ratio by which it exceeds 0; for that which exceeds must be
divisible into the excess + that which is exceeded, so that will be
what it exceeds 0 by + 0. For this reason, too, a line does not
exceed a point unless it is composed of points! Similarly the void
can bear no ratio to the full, and therefore neither can movement
through the one to movement through the other, but if a thing moves
through the thickest medium such and such a distance in such and
such a time, it moves through the void with a speed beyond any
ratio. For let Z be void, equal in magnitude to B and to D. Then if
A is to traverse and move through it in a certain time, H, a time
less than E, however, the void will bear this ratio to the full.
But in a time equal to H, A will traverse the part O of A. And it
will surely also traverse in that time any substance Z which
exceeds air in thickness in the ratio which the time E bears to the
time H. For if the body Z be as much thinner than D as E exceeds H,
A, if it moves through Z, will traverse it in a time inverse to the
speed of the movement, i.e. in a time equal to H. If, then, there
is no body in Z, A will traverse Z still more quickly. But we
supposed that its traverse of Z when Z was void occupied the time
H. So that it will traverse Z in an equal time whether Z be full or
void. But this is impossible. It is plain, then, that if there is a
time in which it will move through any part of the void, this
impossible result will follow: it will be found to traverse a
certain distance, whether this be full or void, in an equal time;
for there will be some body which is in the same ratio to the other
body as the time is to the time.
    To sum the matter up, the cause of this result is obvious, viz.
that between any two movements there is a ratio (for they occupy
time, and there is a ratio between any two times, so long as both
are finite), but there is no ratio of void to full.
    These are the consequences that result from a difference in the
media; the following depend upon an excess of one moving body over
another. We see that bodies which have a greater impulse either of
weight or of lightness, if they are alike in other respects, move
faster over an equal space, and in the ratio which their magnitudes
bear to each other. Therefore they will also move through the void
with this ratio of speed. But that is impossible; for why should
one move faster? (In moving through plena it must be so; for the
greater divides them faster by its force. For a moving thing
cleaves the medium either by its shape, or by the impulse which the
body that is carried along or is projected possesses.) Therefore
all will possess equal velocity. But this is impossible.
    It is evident from what has been said, then, that, if there is a
void, a result follows which is the very opposite of the reason for
which those who believe in a void set it up. They think that if
movement in respect of place is to exist, the void cannot exist,
separated all by itself; but this is the same as to say that place
is a separate cavity; and this has already been stated to be
impossible.
    But even if we consider it on its own merits the so-called
vacuum will be found to be really vacuous. For as, if one puts a
cube in water, an amount of water equal to the cube will be
displaced; so too in air; but the effect is imperceptible to sense.
And indeed always in the case of any body that can be displaced,
must, if it is not compressed, be displaced in the direction in
which it is its nature to be displaced-always either down, if its
locomotion is downwards as in the case of earth, or up, if it is
fire, or in both directions-whatever be the nature of the inserted
body. Now in the void this is impossible; for it is not body; the
void must have penetrated the cube to a distance equal to that
which this portion of void formerly occupied in the void, just as
if the water or air had not been displaced by the wooden cube, but
had penetrated right through it.
    But the cube also has a magnitude equal to that occupied by the
void; a magnitude which, if it is also hot or cold, or heavy