88 SCIENTIFIC INVESTIGATION 



" 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 experi- 

 ence 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 con- 

 vinced 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 veri- 

 fications 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 pos- 

 sible 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 



