The Advance of Science in the Last Half-Century | Page 6

jubilee year of the British Association.[D] And, with respect to
the biological sciences, with some parts of which my studies have
familiarised me, my personal experience nearly coincides with the
preceding half-century. I may hope, therefore, that my chance of
escaping serious errors is as good as that of anyone else, who might
have been persuaded to undertake the somewhat perilous enterprise in
which I find myself engaged.
There is yet another prefatory remark which it seems desirable I should
make. It is that I think it proper to confine myself to the work done,

without saying anything about the doers of it. Meddling with questions
of merit and priority is a thorny business at the best of times, and unless
in case of necessity, altogether undesirable when one is dealing with
contemporaries. No such necessity lies upon me, and I shall, therefore,
mention no names of living men, lest, perchance, I should incur the
reproof which the Israelites, who struggled with one another in the field,
addressed to Moses--'Who made thee a prince and a judge over us.'
[Sidenote: The aim of physical science]
Physical science is one and indivisible. Although, for practical
purposes, it is convenient to mark it out into the primary regions of
Physics, Chemistry, and Biology, and to subdivide these into
subordinate provinces, yet the method of investigation and the ultimate
object of the physical inquirer are everywhere the same.
[Sidenote: the discovery of the rational order of the universe]
The object is the discovery of the rational order which pervades the
universe, the method consists of observation and experiment (which is
observation under artificial conditions) for the determination of the
facts of nature, of inductive and deductive reasoning for the discovery
of their mutual relations and connection. The various branches of
physical science differ in the extent to which at any given moment of
their history, observation on the one hand, or ratiocination on the other,
is their more obvious feature, but in no other way, and nothing can be
more incorrect than the assumption one sometimes meets with, that
physics has one method, chemistry another, and biology a third.
[Sidenote: It is based on postulates]
All physical science starts from certain postulates. One of them is the
objective existence of a material world. It is assumed that the
phenomena which are comprehended under this name have a
'substratum' of extended, impenetrable, mobile substance, which
exhibits the quality known as inertia, and is termed matter.[E] Another
postulate is the universality of the law of causation; that nothing
happens without a cause (that is, a necessary precedent condition), and

that the state of the physical universe, at any given moment, is the
consequence of its state at any preceding moment. Another is that any
of the rules, or so-called 'laws of nature,' by which the relation of
phenomena is truly defined, is true for all time. The validity of these
postulates is a problem of metaphysics; they are neither self-evident nor
are they, strictly speaking, demonstrable. The justification of their
employment, as axioms of physical philosophy, lies in the circumstance
that expectations logically based upon them are verified, or, at any rate,
not contradicted, whenever they can be tested by experience.
[Sidenote: and uses hypotheses.]
Physical science therefore rests on verified or uncontradicted
hypotheses; and, such being the case, it is not surprising that a great
condition of its progress has been the invention of verifiable hypotheses.
It is a favorite popular delusion that the scientific inquirer is under a
sort of moral obligation to abstain from going beyond that
generalisation of observed facts which is absurdly called 'Baconian'
induction. But anyone who is practically acquainted with scientific
work is aware that those who refuse to go beyond fact, rarely get as far
as fact; and anyone who has studied the history of science knows that
almost every great step therein has been made by the 'anticipation of
Nature,' that is, by the invention of hypotheses, which, though
verifiable, often had very little foundation to start with; and, not
unfrequently, in spite of a long career of usefulness, turned out to be
wholly erroneous in the long run.
[Sidenote: Fruitful use of an hypothesis even when wrong.]
The geocentric system of astronomy, with its eccentrics and its
epicycles, was an hypothesis utterly at variance with fact, which
nevertheless did great things for the advancement of astronomical
knowledge. Kepler was the wildest of guessers. Newton's corpuscular
theory of light was of much temporary use in optics, though nobody
now believes in it; and the undulatory theory, which has superseded the
corpuscular theory and has proved one of the most fertile of
instruments of research, is based on the hypothesis of the existence of
an 'ether,' the properties of which are defined in propositions, some of

which, to ordinary apprehension,