EXAMPLES OF THE FOUR METHODS. 479 



plicated inquiries, to go much beyond the initial steps, without 

 calling in the instrument of Deduction, and the temporary 

 aid of hypotheses ; as I myself, in common with Dr. Whewell, 

 have maintained against the purely empirical school. Since 

 therefore such cases could not conveniently be selected to il- 

 lustrate the principles of mere observation and experiment, 

 Dr. Whewell is misled by their absence into representing 

 the Experimental Methods as serving no purpose in scientific 

 investigation ; forgetting that if those methods had not sup- 

 plied the first generalizations, there would have been no mate- 

 rials for his own conception of Induction to work upon. 



His challenge, however, to point out which of the four 

 methods are exemplified in certain important cases of scientific 

 inquiry, is easily answered. " The planetary paths," as far as 

 they are a case of induction at all,* fall under the Method of 

 Agreement. The law of " falling bodies," namely that they 

 describe spaces proportional to the squares of the times, was 

 historically a deduction from the first law of motion ; but the 

 experiments by which it was verified, and by which it might 

 have been discovered, were examples of the Method of Agree- 

 ment; and the apparent variation from the true law, caused 

 by the resistance of the air, was cleared up by experiments 

 in vacuo, constituting an application of the Method of Dif- 

 ference. The law of "refracted rays" (the constancy of the 

 ratio between the sines of incidence and of refraction for each 

 refracting substance) was ascertained by direct measurement, 

 and therefore by the Method of Agreement. The " cosmical 

 motions" were determined by highly complex processes of 

 thought, in which Deduction was predominant, but the 

 Methods of Agreement and of Concomitant Variations had a 

 large part in establishing the empirical laws. Every case 

 without exception of " chemical analysis" constitutes a well- 

 marked example of the Method of Difference. To any one 

 acquainted with the subjects to Dr. Whewell himself, there 

 would not be the smallest difficulty in setting out " the ABO 

 and a b c elements" of these cases. 



* See, on this point, the second chapter of the present Book. 



