ive one:--_i.e._, after the manner of Euclid he starts with a few
simple principles, and then, by a chain of reasoning, endeavours to
deduce from them their consequences, and so to build up bit by bit an
edifice of connected knowledge. In this he was the precursor of Newton.
This method, when rigorously pursued, is the most powerful and
satisfactory of all, and results in an ordered province of science far
superior to the fragmentary conquests of experiment. But few indeed are
the men who can handle it safely and satisfactorily: and none without
continual appeals to experiment for verification. It was through not
perceiving the necessity for verification that he erred. His importance
to science lies not so much in what he actually discovered as in his
anticipation of the right conditions for the solution of problems in
physical science. He in fact made the discovery that Nature could after
all be interrogated mathematically--a fact that was in great danger of
remaining unknown. For, observe, that the mathematical study of Nature,
the discovery of truth with a piece of paper and a pen, has a perilous
similarity at first sight to the straw-thrashing subtleties of the
Greeks, whose methods of investigating nature by discussing the meaning
of words and the usage of language and the necessities of thought, had
proved to be so futile and unproductive.

A reaction had set in, led by Galileo, Gilbert, and the whole modern
school of experimental philosophers, lasting down to the present
day:--men who teach that the only right way of investigating Nature is
by experiment and observation.

It is indeed a very right and an absolutely necessary way; but it is not
the only way. A foundation of experimental fact there must be; but upon
this a great structure of theoretical deduction can be based, all
rigidly connected together by pure reasoning, and all necessarily as
true as the premises, provided no mistake is made. To guard against the
possibility of mistake and oversight, especially oversight, all
conclusions must sooner or later be brought to the test of experiment;
and if disagreeing therewith, the theory itself must be re-examined,
and the flaw discovered, or else the theory must be abandoned.

Of this grand method, quite different from the gropings in the dark of
Kepler--this method, which, in combination with experiment, has made
science what it now is--this which in the hands of Newton was to lead to
such stupendous result