you find is hard and green, you say, “All hard and green apples are sour; this apple is hard and green, therefore this apple is sour.”  That train of reasoning is what logicians call a syllogism, and has all its various parts and terms,—­its major premiss, its minor premiss and its conclusion.  And, by the help of further reasoning, which, if drawn out, would have to be exhibited in two or three other syllogisms, you arrive at your final determination, “I will not have that apple.”  So that, you see, you have, in the first place, established a law by induction, and upon that you have founded a deduction, and reasoned out the special particular case.  Well now, suppose, having got your conclusion of the law, that at some time afterwards, you are discussing the qualities of apples with a friend:  you will say to him, “It is a very curious thing,—­but I find that all hard and green apples are sour!” Your friend says to you, “But how do you know that?” You at once reply, “Oh, because I have tried them over and over again, and have always found them to be so.”  Well, if we were talking science instead of common sense, we should call that an experimental verification.  And, if still opposed, you go further, and say, “I have heard from the people in Somersetshire and Devonshire, where a large number of apples are grown, that they have observed the same thing.  It is also found to be the case in Normandy, and in North America.  In short, I find it to be the universal experience of mankind wherever attention has been directed to the subject.”  Whereupon, your friend, unless he is a very unreasonable man, agrees with you, and is convinced that you are quite right in the conclusion you have drawn.  He believes, although perhaps he does not know he believes it, that the more extensive verifications are,—­that the more frequently experiments have been made, and results of the same kind arrived at,—­that the more varied the conditions under which the same results are 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