52 THE POPULAR SCIENCE MONTHLY. 



who carries an umbrella on a cloudy day does so from reasoning 

 by the method of induction. In the former, having given our 

 premises, we at once deduce a conclusion, and our only care is to 

 see that our premises are correct. The inductive method is a far 

 more elaborate and hazardous proceeding, and can only achieve 

 success where patiently and exhaustively carried out. Its opera- 

 tion is thus described : " It requires an exhaustive enumeration of 

 instances in which the given complex effect is present, in which 

 it is not present, and in which it is present in various degrees or 

 amounts. By the process of exclusion or elimination we may dis- 

 cover a phenomenon, constantly present when the effect is present, 

 absent whenever the effect is absent, and varying in degree with 

 the effect." The danger to avoid is an insufficient enumeration of 

 instances. It is this danger that causes such popular delusions as 

 " that it is unlucky to start a voyage on a Friday," or " that for 

 thirteen to sit at a table betokens ill." Macaulay tells of a judge 

 who was in the habit of propounding a theory that the cause of 

 Jacobinism was the bearing of three names, and then demonstrat- 

 ing it by the rules of induction. Not long since a writer in one 

 of the periodicals, noticing that the great majority of the Presi- 

 dents of the United States bore but two names, warned the Ee- 

 publican party against nominating a man for the Presidency who 

 had more ! There is no proposition under heaven, however mon- 

 strous, which may not be reasoned out by the inductive method 

 when so applied.* It led Henry C. Carey to say that "the mate- 

 rial prosperity of this country could be more fully promoted by a 

 ten years' war with Great Britain than it could be in any other 

 way." It will be seen at once wherein the difference between this 

 induction and that which led Newton to the discovery of the law 

 of gravitation consists. The difference is not in the kind, but in 

 the number of instances. Let there be but one instance in which 

 a heavy body having been projected upward failed to return to 

 the ground, and away goes the stability of Mr. Newton's theory. 

 If the believer in the superstition of the number thirteen will 

 make a few experiments, he will very soon relieve himself of his 

 delusion ; and had the sagacious writer reasoned properly, he 

 would have found the names of John Quincy Adams and Ulysses 

 S. Grant ample material with which to annihilate his theory. A 

 further difficulty in the application of the inductive method con- 

 sists in the existence of a multiplicity of causes, and the impossi- 

 bility often of discovering and separating them. Social problems 

 are affected by causes so numerous and so complex that their de- 

 tection and distinction are frequently impossible ; and until we 

 know what they are, can we do more than state that such and 



* " Every man \vho has ever reasoned on this subject has always proved Ms theory, what- 

 ever it wets, by facts and calculations.' 1 '' (Hume's Essay on Balance of Trade.) 



