pon the mass
of earth, and the earth, compressed into an indissoluble union with
the remaining water, becomes rock. Rock, when it is made up of equal
particles, is fair and transparent, but the reverse when of unequal.
Earth is converted into pottery when the watery part is suddenly drawn
away; or if moisture remains, the earth, when fused by fire, becomes,
on cooling, a stone of a black colour. When the earth is finer and of
a briny nature then two half-solid bodies are formed by separating the
water,--soda and salt. The strong compounds of earth and water are not
soluble by water, but only by fire. Earth itself, when not consolidated,
is dissolved by water; when consolidated, by fire only. The cohesion of
water, when strong, is dissolved by fire only; when weak, either by air
or fire, the former entering the interstices, the latter penetrating
even the triangles. Air when strongly condensed is indissoluble by any
power which does not reach the triangles, and even when not strongly
condensed is only resolved by fire. Compounds of earth and water are
unaffected by water while the water occupies the interstices in 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, wh