THE DEDUCTIVE METHOD. 509 



any other than the fourfold method of experimental inquiry, 

 already discussed. A few remarks on the application of that 

 method to cases of the Composition of Causes, are all that is 

 requisite. 



It is obvious that we cannot expect to find the law of a 

 tendency, by an induction from cases in which the tendency 

 is counteracted. The laws of motion could never have been 

 brought to light from the observation of bodies kept at rest 

 by the equilibrium of opposing forces. Even where the ten 

 dency is not, in the ordinary sense of the word, counteracted, 

 but only modified, by having its effects compounded with the 

 effects arising from some other tendency or tendencies, we are 

 still in an unfavourable position for tracing, by means of such 

 cases, the law of the tendency itself. It would have been 

 scarcely possible to discover the law that every body in motion 

 tends to continue moving in a straight line, by an induction 

 from instances in which the motion is deflected into a curve, 

 by being compounded with the effect of an accelerating force. 

 Notwithstanding the resources afforded in this description of 

 cases by the Method of Concomitant Variations, the principles 

 of a judicious experimentation prescribe that the law of each 

 of the tendencies should be studied, if possible, in cases in which 

 that tendency operates alone, or in combination with no agencies 

 but those of which the effect can, from previous knowledge, be 

 calculated and allowed for. 



Accordingly, in the cases, unfortunately very numerous and 

 important, in which the causes do not suffer themselves to be 

 separated and observed apart, there is much difficulty in laying 

 down with due certainty the inductive foundation necessary to 

 support the deductive method. This difficulty is most of all 

 conspicuous in the case of physiological phenomena ; it being 

 seldom possible to separate the different agencies which col 

 lectively compose an organized body, without destroying the 

 very phenomena which it is our object to investigate : 



following life, in creatures we dissect, 



We lose it, in the moment we detect. 



And for this reason I am inclined to the opinion, that phy- 



