568°) THE CAUSES OF THE XI 
verification, and to take care, moreover, that this 
is done intentionally, and not left to a mere acci- 
dent, 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 veri- 
fication 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 unhesitat- 
ing 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, then, 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 posi- — 
tion 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 - 
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