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. For the first may be the hotter in one sense, the second the
hotter in another. Indeed in some of these cases it is impossible to
say simply even whether a thing is hot or not. For the actual
substratum may not itself be hot, but may be hot when coupled witb
heat as an attribute, as would be the case if one attached a single
name to hot water or hot iron. It is after this manner that blood is
hot. In such cases, in those, that is, in which the substratum owes
its heat to an external influence, it is plain that cold is not a mere
privation, but an actual existence.
There is no knowing but that even fire may be another of these
cases. For the substratum of fire may be smoke or charcoal, and though
the former of these is always hot, smoke being an uprising vapour, yet
the latter becomes cold when its flame is extinguished, as also
would oil and pinewood under similar circumstances. But even
substances that have been burnt nearly all possess some heat, cinders,
for example, and ashes, the dejections also of animals, and, among the
excretions, bile; because some residue of heat has been left in them
after their combustion. It is in another sense that pinewood and fat
substances are hot; namely, because they rapidly assume the
actuality of fire.
Heat appears to cause both coagulation and melting. Now such
things as are formed merely of water are solidified by cold, while
such as are formed of nothing but earth are solidified by fire
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