INTERMIXTURE OF EFFECTS. 257 



fiiiislieJ the consideration. It presents, however, so far as direct in- 

 duction apart from deduction is concerned, iniinitoly grtiater diillc id- 

 ties. Wlien a concurrence of causes f^ives rise to a new effect bearing 

 no relatioa to the separate effects of tliosc causes, the resulting phe- 

 nomenon at least stands forth undisguised, inviting attention to its 

 peculia^'ity, and presenting no obstacle to (»ur recognizing its pi'esence 

 or absence among any number of surrounding phenomena. It admits 

 therefore of being easily brought under the canons of induction, pro- 

 \ided instances can be obtained such as those canons require : and the 

 non-occurrence of such instances, or the want of means to produce 

 them artificially, is the real and only difficulty in such investigations ; 

 a difficulty not logical, but in some sort physical.. It is otherwise with 

 cases of what, in a preceding chapter, has been denominated the 

 Composition of Causes. There, the effects of the separate causes do 

 not terminate and give place to others, thereby ceasing to form any 

 part of the phenomenon to be investigated ; on the contrary they still 

 take place, but are intermingled with, and disguised by, the homoge- 

 neous and closely-allied effects of other causes. They are no longer 

 a, b, c, d, e, existing side by side, and continuing to be separately dis- 

 cernible ; they are -\- a, — a, ^ b, — b, 2 b, Sec, some of which cancel 

 one another, while many others do not .appear distinguishably but 

 merge in one sum : forming altogether a result, between which and 

 the causes whereby it was produced there is often an insurmountable 

 difficulty in tracing by observation any lixeil relation whatever. 



The general idea of the Composition of Causes has been seen to be, 

 that although two or more laws interfere with one another, and appa- 

 rently frustrate or modify one another's operation, yet in reality all 

 are fulfilled, the collective effect being the exact sum total of the 

 effects of the causes taken separately. A familiar instance is that of a 

 body kept in equilibrium by two equal and contrary foixes. One of 

 the forces if acting alone would carry it so far to the west, the other if 

 acting alone would carry it exactly as far towards the cast : and the 

 result is the same as if it had been first carried to the west as far as 

 the one force would carry it, and then back towards the east as far as 

 the other would caiTy it, that is, precisely the same distance ; being 

 ultimately left where it was found at first. 



All laws of causation are liable to be in this manner counteracted, 

 and seemingly frustrated, by coming into conflict with other laws, the 

 separate result of which is cjpposite to theirs, or more or less incon- 

 sistent with it. And hence, with almost every law, many instances in 

 which it really is entirely fulfilled, do not, at first siglit, appear to be 

 cases of its operation at all. It is so in the example just adduced : a 

 force, in mechanics, means neither more nor less than a cause of 

 motion, yet the sum ofthe effects of two causes of motion may be rest. 

 Again, a bcjdy solicited by two forces in directions making an angle 

 with one another, moves in the diagonal; and it seems a paradox to 

 say that motion in the diagonal is flhe sum of two motions in two other 

 lines. Motion, however, is but changes of place, and at every instant 

 the body is in the exact place it would have been in if the forces liad 

 acted during alternate instants instead of acting in the same instant; 

 (saving that if we' suppose two forces to act successively which are in 

 truth simultaneous, we must of course allow them double the time.) 

 It is evident, therefore, that each force has had, during eaeh uistant, 

 Kk 



