portion would then contain only one molecule, an individual body, one
and indivisible, unalterable by any power in nature.

Even in our ordinary experiments on very finely divided matter we find
that the substance is beginning to lose the properties which it
exhibits when in a large mass, and that effects depending on the
individual action of molecules are beginning to become prominent.

The study of these phenomena is at present the path which leads to the
development of molecular science.

That superficial tension of liquids which is called capillary
attraction is one of these phenomena. Another important class of
phenomena are those which are due to that motion of agitation by which
the molecules of a liquid or gas are continually working their way
from one place to another, and continually changing their course, like
people hustled in a crowd.

On this depends the rate of diffusion of gases and liquids through
each other, to the study of which, as one of the keys of molecular
science, that unwearied inquirer into nature's secrets, the late Prof.
Graham, devoted such arduous labour.

The rate of electrolytic conduction is, according to Wiedemann's
theory, influenced by the same cause; and the conduction of heat in
fluids depends probably on the same kind of action. In the case of
gases, a molecular theory has been developed by Clausius and others,
capable of mathematical treatment, and subjected to experimental
investigation; and by this theory nearly every known mechanical
property of gases has been explained on dynamical principles; so that