310 INDUCTION. 



torically 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 Agreement; and the apparent variation from 

 the true law, caused by the resistance of the air, was cleared up by experi- 

 ments in vacuo, constituting an application of the Method of Difference. 

 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 Agree- 

 ment and of Concomitant Variations had a large part in establishing the 

 empirical laws. Every case without exception of "chemical analysis" con- 

 stitutes a well-marked example of the Method of Diffei'ence. To any one 

 acquainted with the subjects — to Dr. Whewell himself, there would not be 

 the smallest difficulty in setting out " the ABC and ah c elements " of 

 these cases. 



If discoveries are ever made by observation and experiment without De- 

 duction, the four methods ai-e methods of discovery : but even if they were 

 not methods of discovery, it would not be the less true that they are the 

 sole methods of Proof; and in that character, even the results of deduction 

 are amenable to them. The great generalizations which begin as Hypo- 

 theses, must end by being proved, and are in reality (as will be shown 

 hereafter) proved, by the Four Methods. Now it is with Proof, as such, 

 that Logic is principally concerned. This distinction has indeed no chance 

 of finding favor with Dr. Whewell; for it is the peculiarity of his system, 

 not to recognize, in cases of Induction, any necessity for proof. If, after 

 assuming an hypothesis and carefully collating it with facts, nothing is 

 brought to light inconsistent with it, that is, if experience does not <:?/sprove 

 it, he is content: at least until a simpler hypothesis, equally consistent with 

 experience, presents itself. If this be Induction, doubtless there is no ne- 

 cessity for the four methods. But to suppose that it is so, appears to me a 

 radical misconception of the nature of the evidence of physical truths. 



So real and practical is the need of a test for induction, similar to the 

 syllogistic test of ratiocination, that inferences which bid defiance to the 

 most elementary notions of inductive logic are put forth without misgiv- 

 ing by persons eminent in physical science, as soon as they are off the 

 ground on which they are conversant with the facts, and not reduced to 

 judge only by the arguments; and as for educated persons in general, it 

 may be doubted if they are better judges of a good or a bad induction 

 than they were before Bacon wrote. The improvement in the results of 

 thinking has seldom extended to the processes ; or has reached, if any proc- 

 ess, that of investigation only, not that of proof. A knowledge of many 

 laws of nature has doubtless been arrived at, by frafning hypotheses and 

 finding that the facts corresponded to them; and many errors have been 

 got rid of by coming to a knowledge of facts which were inconsistent with 

 them, but not by discovering that the mode of thought which led to the 

 errors was itself faulty, and might have been known to be such independ- 

 ently of the facts which disproved the specific conclusion. Hence it is, 

 that while the thoughts of mankind have on many subjects worked them- 

 selves practically right, the thinking power remains as weak as ever : and 

 on all subjects on which the facts which would check the result are not ac- 

 cessible, as in what relates to the invisible world, and even, aa has been 

 seen lately, to the visible world of the planetary regions, meu ol the great- 



