The Advance of Science in the Last Half-Century | Page 8

distinctly, in former periods of the history of science; and, so far is
either from being the outcome of purely inductive reasoning, that it
would be hard to overrate the influence of metaphysical, and even of
theological, considerations upon the development of all three. The
peculiar merit of our epoch is that it has shown how these hypotheses
connect a vast number of seemingly independent partial generalisations;
that it has given them that precision of expression which is necessary
for their exact verification; and that it has practically proved their value
as guides to the discovery of new truth. All three doctrines are
intimately connected, and each is applicable to the whole physical
cosmos. But, as might have been expected from the nature of the case,
the first two grew, mainly, out of the consideration of physico-chemical
phenomena; while the third, in great measure, owes its rehabilitation, if
not its origin, to the study of biological phenomena.
[Sidenote: (1) Molecular constitution of matter.]
In the early decades of this century, a number of important truths
applicable, in part, to matter in general, and, in part, to particular forms
of matter, had been ascertained by the physicists and chemists.
The laws of motion of visible and tangible, or molar, matter had been
worked out to a great degree of refinement and embodied in the
branches of science known as Mechanics, Hydrostatics, and
Pneumatics. These laws had been shown to hold good, so far as they
could be checked by observation and experiment, throughout the
universe, on the assumption that all such masses of matter possessed
inertia and were susceptible of acquiring motion, in two ways, firstly
by impact, or impulse from without; and, secondly, by the operation of
certain hypothetical causes of motion termed 'forces,' which were

usually supposed to be resident in the particles of the masses
themselves, and to operate at a distance, in such a way as to tend to
draw any two such masses together, or to separate them more widely.
[Sidenote: The two theories as to matter.]
With respect to the ultimate constitution of these masses, the same two
antagonistic opinions which had existed since the time of Democritus
and of Aristotle were still face to face. According to the one, matter
was discontinuous and consisted of minute indivisible particles or
atoms, separated by a universal vacuum; according to the other, it was
continuous, and the finest distinguishable, or imaginable, particles were
scattered through the attenuated general substance of the plenum. A
rough analogy to the latter case would be afforded by granules of ice
diffused through water; to the former, such granules diffused through
absolutely empty space.
[Sidenote: Reassertion by Dalton of atomic theory.]
In the latter part of the eighteenth century, the chemists had arrived at
several very important generalisations respecting those properties of
matter with which they were especially concerned. However plainly
ponderable matter seemed to be originated and destroyed in their
operations, they proved that, as mass or body, it remained
indestructible and ingenerable; and that, so far, it varied only in its
perceptibility by our senses. The course of investigation further proved
that a certain number of the chemically separable kinds of matter were
unalterable by any known means (except in so far as they might be
made to change their state from solid to fluid, or vice versâ), unless
they were brought into contact with other kinds of matter, and that the
properties of these several kinds of matter were always the same,
whatever their origin. All other bodies were found to consist of two or
more of these, which thus took the place of the four 'elements' of the
ancient philosophers. Further, it was proved that, in forming chemical
compounds, bodies always unite in a definite proportion by weight, or
in simple multiples of that proportion, and that, if any one body were
taken as a standard, every other could have a number assigned to it as
its proportional combining weight. It was on this foundation of fact that

Dalton based his re-establishment of the old atomic hypothesis on a
new empirical foundation. It is obvious, that if elementary matter
consists of indestructible and indivisible particles, each of which
constantly preserves the same weight relatively to all the others,
compounds formed by the 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