THE FIGURES OF THE ELEMENTS.

Of the figures of the elements; and first as against those who deny
the opinions of Plato, and who say that if the elements include one
another in the forms attributed to them by Plato they would cause a
vacuum one within the other. I say it is not true, and I here prove
it, but first I desire to propound some conclusions. It is not
necessary that the elements which include each other should be of
corresponding magnitude in all the parts, of that which includes and
of that which is included. We see that the sphere of the waters
varies conspicuously in mass from the surface to the bottom, and
that, far from investing the earth when that was in the form of a
cube that is of 8 angles as Plato will have it, that it invests the
earth which has innumerable angles of rock covered by the water and
various prominences and concavities, and yet no vacuum is generated
between the earth and water; again, the air invests the sphere of
waters together with the mountains and valleys, which rise above
that sphere, and no vacuum remains between the earth and the air, so
that any one who says a vacuum is generated, speaks foolishly.

But to Plato I would reply that the surface of the figures which
according to him the elements would have, could not exist.

That the flow of rivers proves the slope of the land.