advanced of our modern philosophers are clear in their mind that all
we know as to the order of Nature is that, given certain conditions,
certain consequences inevitably follow.

Although the limitations which modern men of science perceive to be
put upon their labours may seem at first sight calculated to confine
our understanding within a narrow field of things which can be seen,
or in some way distinctly proved to exist, the effect of this
limitation has been to make science what it is--a realm of things
known as distinct from things which may be imagined. All the
difference between ancient science and modern consists in the fact
that in modern science inquirers demand a businesslike method in the
interpretation of Nature. Among the Greeks the philosopher who taught
explanations of any feature in the material world which interested him
was content if he could imagine some way which would account for the
facts. It is the modern custom now to term the supposition of an
explanation a _working hypothesis_, and only to give it the name of
theory after a very careful search has shown that all the facts which
can be gathered are in accordance with the view. Thus when Newton made
his great suggestion concerning the law of gravitation, which was to
the effect that all bodies attracted each other in proportion to
their masses, and inversely as the square of their distance from each
other, he did not rest content, as the old Greeks would have done,
with the probable truth of the explanation, but carefully explored the
movements of the planets and satellites of the solar system to see if
the facts accorded with the hypothesis. Even the perfect
correspondence which he found did not entirely content inquirers, and
in this century very important experiments have been made which have
served to show that a ball suspended in front of a precipice will be
attracted toward the steep, and that even a mass of lead some tons in