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Page:Popular Science Monthly Volume 38.djvu/62

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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 operation 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 discover 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 demonstrating it by the rules of induction. Not long since a writer in one of the periodicals, noticing that the great majority of the Presidents of the United States bore but two names, warned the Republican party against nominating a man for the Presidency who had more! There is no proposition under heaven, however monstrous, which may not be reasoned out by the inductive method when so applied.[1] It led Henry C. Carey to say that "the material 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 consists in the existence of a multiplicity of causes, and the impossibility often of discovering and separating them. Social problems are affected by causes so numerous and so complex that their detection and distinction are frequently impossible; and until we know what they are, can we do more than state that such and


  1. "Every man who has ever reasoned on this subject has always proved his theory, whatever it was, by facts and calculations." (Hume's Essay on Balance of Trade.)