hey would not have
sufficed to overcome the repugnance of certain physicists for
speculations which, an imposing mathematical baggage notwithstanding,
seemed to them too hypothetical. The theory, moreover, stopped at the
molecule, and appeared to suggest no idea which could lead to the
discovery of the key to the phenomena where molecules exercise a
mutual influence on each other. The kinetic hypothesis, therefore,
remained in some disfavour with a great number of persons,
particularly in France, until the last few years, when all the recent
discoveries of the conductivity of gases and of the new radiations
came to procure for it a new and luxuriant efflorescence. It may be
said that the atomistic synthesis, but yesterday so decried, is to-day
triumphant.

The elements which enter into the earlier kinetic theory, and which,
to avoid confusion, should be always designated by the name of
molecules, were not, truth to say, in the eyes of the chemists, the
final term of the divisibility of matter. It is well known that, to
them, except in certain particular bodies like the vapour of mercury
and argon, the molecule comprises several atoms, and that, in compound
bodies, the number of these atoms may even be fairly considerable. But
physicists rarely needed to have recourse to the consideration of
these atoms. They spoke of them to explain certain particularities of
the propagation of sound, and to enunciate laws relating to specific
heats; but, in general, they stopped at the consideration of the
molecule.

The present theories carry the division much further. I shall not
dwell now on these theories, since, in order to thoroughly understand
them, many other facts must be examined. But to avoid all confusion,
it remains understood that, contrary, no doubt, to etymology, but in
conformity with present custom, I shall continue in what follows to
call atoms those particles of matter which have till now been spoken
of; these atoms being themselves, according to modern views,
singularly complex edifices formed of elements, of which we shall have
occasion to indicate the nature later.

CHAPTER IV

THE VARIOUS STATES OF MATTER

Sec. 1. THE STATICS OF FLUIDS

The division of bodies into gaseous, liquid, and solid, and the
distinction established for the same substance between the three
states, retain a great importance for the applications and usages of
daily life, but have long since lost their absolute value from th