ion, What do
you mean by explaining a property of matter? to be put cynically, and
letting ourselves be irritated by it, suppose we give to the questioner
credit for being sympathetic, and condescend to try and answer his
question. We find it not very easy to do so. All the properties of matter
are so connected that we can scarcely imagine one _thoroughly explained_
without our seeing its relation to all the others, without in fact having
the explanation of all; and till we have this we cannot tell what we mean
by "explaining a property" or "explaining the properties" of matter. But
though this consummation may never be reached by man, the progress of
science may be, I believe will be, step by step toward it, on many
different roads converging toward it from all sides. The kinetic theory of
gases is, as I have said, a true step on one of the roads. On the very
distinct road of chemical science, St. Claire Deville arrived at his grand
theory of dissociation without the slightest aid from the kinetic theory of
gases. The fact that he worked it out solely from chemical observation and
experiment, and expounded it to the world without any hypothesis whatever,
and seemingly even without consciousness of the beautiful explanation it
has in the kinetic theory of gases, secured for it immediately an
independent solidity and importance as a chemical theory when he first
promulgated it, to which it might even by this time scarcely have attained
if it had first been suggested as a probability indicated by the kinetic
theory of gases, and been only afterward confirmed by observation. Now,
however, guided by the views which Clausius and Williamson have given us of
the continuous interchange of partners between the compound molecules
constituting chemical compounds in the gaseous state, we see in Deville's
theory of dissociation a point of contact of the most transcendent interest
between the chemical and physical lines of scientific progress.

To return to elasticity: if we could make out of matter devoid of
elasticity a combined system of relatively moving parts which, in virtue of
motion, has the essential characteristics of an elastic body, this would
surely be, if not positively a step in the kinetic theory of matter, at
least a fingerpost pointing a way which we may hope will lead to a kinetic
theory of matter. Now this, as I have already shown,[1] we can do in
several ways. In the case of the last of the communications referred