of the same kind arrived at,--that the more varied the conditions under
which the same results have been attained, the more certain is the
ultimate conclusion, and he disputes the question no further. He sees
that the experiment has been tried under all sorts of conditions, as to
time, place, and people, with the same result; and he says with you,
therefore, that the law you have laid down must be a good one, and he
must believe it.

In science we do the same thing;--the philosopher exercises precisely
the same faculties, though in a much more delicate manner. In
scientific inquiry it becomes a matter of duty to expose a supposed law
to every possible kind of verification, and to take care, moreover,
that this is done intentionally, and not left to a mere accident, as in
the case of the apples. And in science, as in common life, our
confidence in a law is in exact proportion to the absence of variation
in the result of our experimental verifications. For instance, if you
let go your grasp of an article you may have in your hand, it will
immediately fall to the ground. That is a very common verification of
one of the best established laws of nature--that of gravitation. The
method by which men of science establish the existence of that law is
exactly the same as that by which we have established the trivial
proposition about the sourness of hard and green apples. But we
believe it in such an extensive, thorough, and unhesitating manner
because the universal experience of mankind verifies it, and we can
verify it ourselves at any time; and that is the strongest possible
foundation on which any natural law can rest.

So much by way of proof that the method of establishing laws in science
is exactly the same as that pursued in common life. Let us now turn to
another matter (though really it is but another phase of the same