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.
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