434 INDUCTION. 



arise from the separate agency of the same causes : 

 the laws of these new effects being again susceptible 

 of composition, to an indefinite extent, like the laws 

 which they superseded. 



-J. That effects are proportional to their causes 

 is laid down, by some writers, as an axiom in the 

 theory of causation ; and great use is sometimes made 

 of this principle in reasonings respecting the laws of 

 nature, although it is incumbered with many difficul- 

 ties and apparent exceptions, which much ingenuity 

 has been expended in showing not to be real ones. 

 This proposition, in so far as it is true, enters as a 

 particular case into the general principle of the Com- 

 position of Causes : the causes compounded being, in 

 this instance, homogeneous ; in which case, if in any, 

 their joint effect might be expected to be identical 

 with the sum of their separate effects. If a force 

 equal to one hundred weight, will raise a certain body 

 along an inclined plane, a force equal to two hundred 

 weight will, we know, raise two bodies exactly similar, 

 and thus the effect is proportional to the cause. But 

 does not a force equal to two hundred weight, actually 

 contain in itself two forces each equal to one hundred 

 weight, which, if employed apart, would separately 

 raise the two bodies in question ? The fact, therefore, 

 that when exerted jointly they raise both bodies at once, 

 results from the Composition of Causes, and is a mere 

 instance of the general fact that mechanical forces are 

 subject to the law of Composition. And so in every 

 other case which can be supposed. For the doctrine 

 of the proportionality of effects to their causes cannot 

 of course be applicable to cases in which the augmen- 

 tation of the cause alters the kind of effect ; that is, 

 in which the surplus quantity superadded to the cause 



