ting observations, by repeating them, averaging them, verifying
one experimental process by another, always refining the methods of
exact measurement, multiplying the opportunities of error (that if any
exist it may at last show itself), and by other devices of what may be
called Material Logic or Methodology. But only direct experience and
personal manipulation of scientific processes, can give a just sense of
their effectiveness; and to stand by, suggesting academic doubts, is
easier and more amusing.

Sec. 2. Still, it is not so much in laws based upon direct observation or
experiment, that the material validity of scientific reasoning appears,
as in the cumulative evidence that arises from the co-ordination of laws
within each science, and the growing harmony and coherence of all
sciences. This requires a more elaborate combination of deduction with
observation and experiment. During the last three hundred years many
departments of science have been reduced under principles of the
greatest generality, such as the Conservation of Energy, the Law of
Gravitation, the Undulatory theory of Light, the Law of combining
Equivalents, and the Theory of Natural Selection; connecting and
explaining the less general laws, which, again, are said to connect and
explain the facts. Meanwhile, those sciences that were the first to make
progress have helped to develop others which, like Biology and
Sociology, present greater difficulties; and it becomes more and more
apparent that the distinctions drawn among sciences are entirely for the
convenience of study, and that all sciences tend to merge in one
universal Science of Nature. Now, this process of the 'unification of
knowledge' is almost another name for deduction; but at the same time it
depends for its reality and solidity upon a constant reference to
observation and experiment. Only a very inadequate notion of it can be
given in the ensuing chapters.

We saw in chap. xiv. Sec. 6, that when two or more agents or forces combine
to produce a phenomenon, their effects are intermixed in it, and this in
one of two ways according to their nature. In chemical action and in
vegetable and animal life, the causal agents concerned are blended in
their results in such a way that most of the qualities which they
exhibited severally are lost, whilst new qualities appear instead. Thus
chlorine (a greenish-yellow gas) and sodium (a metal) unite to form
common salt NaCl; which is quite unlike e