On The Parts Of Animals   

which the more readily melts a fusible substance, or sets on fire an
inflammable one. Again, of two masses of one and the same substance,
the larger is said to have more heat than the smaller. Again, of two
bodies, that is said to be the hotter which takes the longer time in
cooling, as also we call that which is rapidly heated hotter than that
which is long about it; as though the rapidity implied proximity and
this again similarity of nature, while the want of rapidity implied
distance and this again dissimilarity of nature. The term hotter is
used then in all the various senses that have been mentioned, and
perhaps in still more. Now it is impossible for one body to be hotter
than another in all these different fashions. Boiling water for
instance, though it is more scalding than flame, yet has no power of
burning or melting combustible or fusible matter, while flame has. So
again this boiling water is hotter than a small fire, and yet gets
cold more rapidly and completely. For in fact fire never becomes cold;
whereas water invariably does so. Boiling water, again, is hotter to
the touch than oil; yet it gets cold and solid more rapidly than this
other fluid. Blood, again, is hotter to the touch than either water or
oil, and yet coagulates before them. Iron, again, and stones and other
similar bodies are longer in getting heated than water, but when once
heated burn other substances with a much greater intensity. Another
distinction is this. In some of the bodies which are called hot the
heat is derived from without, while in others it belongs to the bodies
themselves; and it makes a most important difference whether the heat
has the former or the latter origin. For to call that one of two
bodies the hotter, which is possessed of heat, we may almost say,
accidentally and not of its own essence, is very much the same thing
as if, finding that some man in a fever was a musician, one were to
say that musicians are hotter than healthy men. Of that which is hot
per se and that which is hot per accidens, the former is the slower to
cool, while not rarely the latter is the hotter to the touch. The
former again is the more burning of the two-flame, for instance, as
compared with boiling water-while the latter, as the boiling water,
which is hot per accidens, is the more heating to the touch. From all
this it is clear that it is no simple matter to decide which of two
bodies is the hotter. 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. Hot substances
again are solidified by cold, and, when they consist chiefly of earth,
the process of solidification is rapid, and the resulting substance is
insoluble; but, when their main constituent is water, the solid matter
is again soluble. What kinds of substances, however, admit of being
solidified, and what are the causes of solidification, are questions
that have already been dealt with more precisely in another treatise.
In conclusion, then, seeing that the terms hot and hotter are used in