554 INDUCTION. 



bined causes is resolved into the separate laws of the 

 causes, the nature of the case implies that the law of 

 the effect is less general than the law of any of the 

 causes, since it only holds when they are combined; 

 while the law of any one of the causes holds good 

 both then, and also when that cause acts apart from 

 the rest. It is also manifest that the complex law is 

 liable to be oftener unfulfilled, than any one of the 

 simpler laws of which it is the result, since every con- 

 tingency which defeats any of the laws prevents so 

 much of the effect as depends upon it, and thereby 

 defeats the complex law. The mere rusting, for 

 example, of some small part of a great machine, often 

 suffices entirely to prevent the effect which ought to 

 result from the joint action of all the parts. The 

 law of the effect of a combination of causes is always 

 subject to the whole of the negative conditions which 

 attach to the action of all the causes severally. 



There is another and a still stronger reason why 

 the law of a complex effect must be less general than 

 the laws of the causes which conspire to produce it. 

 The same causes, acting according to the same laws, 

 and differing only in the proportions in which they 

 are combined,, often produce effects which differ not 

 merely in quantity, but in kind. The combination of 

 a tangential with a centripetal force, in the proportions 

 which obtain in all the planets and satellites of our 

 solar system, gives rise to an elliptical motion ; but if 

 the ratio of the two forces to each other were slightly 

 altered, it is demonstrable that the motion produced 

 would be in a circle, or a parabola, or an hyperbola : 

 and it has been supposed that in the case of some 

 comets one of these is really the fact. Yet the law of 

 the parabolic motion would be resolvable into the 

 very same simple laws into which that of the elliptical 



