aggregation of two, three, four, or more such particles must exemplify
the rule of combination in definite proportions deduced from
observation.

In the meanwhile, the gradual reception of the undulatory theory of
light necessitated the assumption of the existence of an 'ether'
filling all space. But whether this ether was to be regarded as a
strictly material and continuous substance was an undecided point, and
hence the revived atomism, escaped strangling in its birth. For it is
clear, that if the ether is admitted to be a continuous material
substance, Democritic atomism is at an end and 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.