e, 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
question), and that is, the method by which, from the relations of
certain phenomena, we prove that some stand in the position of causes
towards the others.

I want to put the case clearly before you, and I will therefore show you
what I mean by another familiar example. I will suppose that one of you,
on coming down in the morning to the parlour of your house, finds that a
tea-pot and some spoons which had been left in the room on the previous
evening are gone,--the window is open, and you observe the mark of a
dirty hand on the window-frame, and perhaps, in addition to that, you
notice the impress of a hob-nailed shoe on the gravel outside. All these
phenomena have struck your attention instantly, and before two minutes
have passed you say, "Oh, somebody has broken open the window, entered
the room, and run off with the spoons and the tea-pot!" That speech is
out of your mouth in a moment. And you will probably add, "I know there
has; I am quite sure of it!" You mean to say exactly what you know; but
in reality what you have said has been the expression of what is, in all
essential particulars, an Hypothesis. You do not 'know' it at all; it is
nothing but an hypothesis rapidly framed in your own mind! And it is an
hypothesis founded on a long train of inductions and deductions.

What