be hot there is fire. This is why flame is burning smoke or dry
exhalation. The fumes of wood are smoke, those of wax and frankincense
and such-like, and pitch and whatever contains pitch or such-like
are sooty smoke, while the fumes of oil and oily substances are a
greasy steam; so are those of all substances which are not at all
combustible by themselves because there is too little of the dry in
them (the dry being the means by which the transition to fire is
effected), but burn very readily in conjunction with something else.
(For the fat is just the conjunction of the oily with the dry.) So
those bodies that give off fumes, like oil and pitch, belong rather to
the moist, but those that burn to the dry.
Homogeneous bodies differ to touch-by these affections and
differences, as we have said. They also differ in respect of their
smell, taste, and colour.
By homogeneous bodies I mean, for instance, 'metals', gold,
copper, silver, tin, iron, stone, and everything else of this kind and
the bodies that are extracted from them; also the substances found
in animals and plants, for instance, flesh, bones, sinew, skin,
viscera, hair, fibres, veins (these are the elements of which the
non-homogeneous bodies like the face, a hand, a foot, and everything
of that kind are made up), and in plants, wood, bark, leaves, roots,
and the rest like them.
The homogeneous bodies, it is true, are constituted by a different
cause, but the matter of which they are composed is the dry and the
moist, that is, water and earth (for these bodies exhibit those
qualities most clearly). The agents are the hot and the cold, for they
constitute and make concrete the homogeneous bodies out of earth and
water as matter. Let us consider, then, which of the homogeneous
bodies are made of earth and which of water, and which of both.