Perhaps they are here unduly severe, since they often admit
too easily the objective existence of quantities which they cannot
define. Thus, for instance, it is usual almost every day to speak of
the heat possessed by a body. Yet no body in reality possesses a
definite quantity of heat even relatively to any initial state; since
starting from this point of departure, the quantities of heat it may
have gained or lost vary with the road taken and even with the means
employed to follow it. These expressions of heat gained or lost are,
moreover, themselves evidently incorrect, for heat can no longer be
considered as a sort of fluid passing from one body to another.
The real reason which makes entropy somewhat mysterious is that this
magnitude does not fall directly under the ken of any of our senses;
but it possesses the true characteristic of a concrete physical
magnitude, since it is, in principle at least, measurable. Various
authors of thermodynamical researches, amongst whom M. Mouret should
be particularly mentioned, have endeavoured to place this
characteristic in evidence.
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