nd Cartesian continuity
takes its place.

[Sidenote: The real value of hypothesis; it predicates the existence
of units of matter.]

The real value of the new atomic hypothesis, however, did not lie in
the two points which Democritus and his followers would have
considered essential--namely, the indivisibility of the 'atoms' and
the presence of an interatomic vacuum--but in the assumption that, to
the extent to which our means of analysis take us, material bodies
consist of definite minute masses, each of which, so far as physical
and chemical processes of division go, may be regarded as a
unit--having a practically permanent individuality. Just as a man is
the unit of sociology, without reference to the actual fact of his
divisibility, so such a minute mass is the unit of physico-chemical
science--that smallest material particle which under any given
circumstances acts as a whole.[F]

The doctrine of specific heat originated in the eighteenth century.
It means that the same mass of a body, under the same circumstances,
always requires the same quantity of heat to raise it to a given
temperature, but that equal masses of different bodies require
different quantities. Ultimately, it was found that the quantities of
heat required to raise equal masses of the more perfect gases, through
equal ranges of temperature, were inversely proportional to their
combining weights. Thus a definite relation was established between
the hypothetical units and heat. The phenomena of electrolytic
decomposition showed that there was a like close relation between
these units and electricity. The quantity of electricity generated by
the combination of any two units is sufficient to separate any other
two which are susceptible of such decomposition. The phenomena of
isomorphism showed a relation between the units and crystalline forms;
certain units are thus able to replace others in a crystalline body
without altering its form, and others are not.

Again, the laws of the effect of pressure and heat on gaseous bodies,
the fact that they combine in definite proportions by volume, and that
such proportion bears a simple relation to their combining weights,
all harmonised with the Daltonian hypothesis, and led to the bold
speculation known as the law of Avogadro--that all gaseous bodies,
under the same physical conditions, contain the same number of units.
In the form in which it was first enunciated, this hypothesis was
incorrect--perhaps