THE DEDUCTIVE METHOD. 331 



case, that case becomes a new experiment on the law, and helps to confirm 

 what it did not assist to discover. It is a new trial of the principle in a 

 different set of circumstances ; and occasionally serves to eliminate some 

 circumstance not previously excluded, and the exclusion of which might 

 require an experiment impossible to be executed. This was strikingly 

 conspicuous in the example formerly quoted, in which the difference be- 

 tween the observed and the calculated velocity of sound was ascertained to 

 result from the heat extricated by the condensation which takes place in 

 each sonorous vibration. This was a trial, in new circumstances, of the 

 law of the development of heat by compression ; and it added materially 

 to the proof of the universality of that law. Accordingly, any law of na- 

 ture is deemed to have gained in point of certainty, by being found to 

 explain some complex case which had not previously been thought of in 

 connection with it ; and this indeed is a consideration to which it is the 

 habit of scientific inquirers to attach rather too much value than too little. 

 To the Deductive Method, thus characterized in its three constituent 

 parts. Induction, Ratiocination, and Verification, the human mind is in- 

 debted for its most conspicuous triumphs in the investigation of nature. 

 To it we owe all the theories by which vast and complicated phenomena 

 are embraced under a few simple laws, which, considered as the laws of 

 those great phenomena, could never have been detected by their direct 

 study. We may form some conception of what the method has done for 

 us from the case of the celestial motions : one of the simplest among the 

 greater instances of the Composition of Causes, since (except in a few cases 

 not of primary importance) each of the heavenly bodies may be consider- 

 ed, without material inaccuracy, to be never at one time influenced by the 

 attraction of more than two bodies, the sun and one other planet or satel- 

 lite ; making, with the reaction of the body itself, and the force generated 

 by the body's own motion and acting in the direction of the tangent, only 

 four different agents on the concurrence of which the motions of that body 

 depend ; a much smaller number, no doubt, than that by which any other 

 of the great phenomena of nature is determined or modified. Yet how 

 could we ever have ascertained the combination of forces on which the 

 motions of the earth and planets are dependent, by merely comparing the 

 orbits or velocities of different planets, or the different velocities or posi- 

 tions of the same planet? Notwithstanding the regularity which mani- 

 fests itself in those motions, in a degree so rare among the effects of con- 

 cun-ence of causes ; and although the periodical recurrence of exactly the 

 same effect, affords positive proof that all the combinations of causes which 

 occur at all, recur periodically; we should not have known what the causes 

 Avere, if the existence of agencies precisely similar on our own earth had 

 not, fortunately, brought the causes themselves within the reach of experi- 

 mentation under simple circumstances. As we shall have occasio;i to an- 

 alyze, further on, this great example of the Method of Deduction, we shall 

 not occupy any time with it here, but shall proceed to that secondary ap- 

 plication of the Deductive Method, the result of which is not to prove laws 

 of phenomena, but to explain them. 



