them, but begin to liquefy when fire enters into the interstices of the
water. They are of two kinds, some of them, like glass, having more earth,
others, like wax, having more water in them.

Having considered objects of sense, we now pass on to sensation. But we
cannot explain sensation without explaining the nature of flesh and of the
mortal soul; and as we cannot treat of both together, in order that we may
proceed at once to the sensations we must assume the existence of body and
soul.

What makes fire burn? The fineness of the sides, the sharpness of the
angles, the smallness of the particles, the quickness of the motion.
Moreover, the pyramid, which is the figure of fire, is more cutting than
any other. The feeling of cold is produced by the larger particles of
moisture outside the body trying to eject the smaller ones in the body
which they compress. The struggle which arises between elements thus
unnaturally brought together causes shivering. That is hard to which the
flesh yields, and soft which yields to the flesh, and these two terms are
also relative to one another. The yielding matter is that which has the
slenderest base, whereas that which has a rectangular base is compact and
repellent. Light and heavy are wrongly explained with reference to a lower
and higher in place. For in the universe, which is a sphere, there is no
opposition of above or below, and that which is to us above would be below
to a man standing at the antipodes. The greater or less difficulty in
detaching any element from its like is the real cause of heaviness or of
lightness. If you draw the earth into the dissimilar air, the particles of
earth cling to their native element, and you more easily detach a small
portion than a large. There would be the same difficulty in moving any of
the upper elements towards the lower. The smooth and the rough are
severally produced by the union of evenness with compactness, and of