INTERMIXTURE OF EFFECTS. 



2«9 



of instances. One set of observations 

 or experiments shows that the sun is 

 a cause of heat, another that friction is 

 a source of it, another that percussion, 

 another that electricity, another that 

 chemical action is such a source. Or 

 (secondly) the plurality may come to 

 light in the course of collating a 

 number of instances, when we attempt 

 to find some circumstance in which 

 they all agree, and fail in doing so. 

 We find it impossible to trace, in all the 

 cases in which the eflfect is met with, 

 any common circumstance. We find 

 that we can eliminate all the ante- 

 cedents ; that no one of them is 

 present in all the instances, no one 

 of them indispensable to the eflfect. 

 On closer scrutiny, however, it appears 

 that though no one is always present, 

 one or other of several always is. If, 

 on further analysis, we can detect in 

 these any common element, we may 

 be able to ascend from them to some 

 one cause which is the really operative 

 circumstance in them all. Thus it is 

 now thought that in the production of 

 heat by friction, percussion, chemical 

 action, &c., the ultimate source is one 

 and the same. But if (as continually 

 happens) we cannot take this ulterior 

 step, the different antecedents must 

 be set down provisionally as distinct 

 causes, each sufficient of itself to pro- 

 duce the eflfect. 



We here close our remarks on the 

 Plurality of Causes, and proceed to 

 the still more peculiar and more com- 

 plex case of the Intermixture of 

 Effects, and the interference of causes 

 with one another : a case constituting 

 the principal part of the complication 

 and difficulty of the study of nature ; 

 and with which the four only possible 

 methods of directly inductive investi- 

 gation by observation and experiment 

 are for the most part, as will appear 

 presently, quite unequal to cope. The 

 instrument of Deduction alone is 

 adequate to unravel the complexities 

 proceeding from this source ; and the 

 four methods have little more in their 

 power than to supply premises for, 

 IMid a verification of, our deductions, 



§ 4. A concurrence of two or mora 

 causes, not separately producing each 

 its own eflfect, but interfering with or 

 modifying the effects of one another, 

 takes place, as has already been 

 explained, in two diflferent ways. 

 In the one, which is exemplified by 

 the joint operation of diflferent forces 

 in mechanics, the separate eflfects of all 

 the causes continue to be produced, but 

 are compounded with one another, and 

 disappear in one total. In the other, 

 illustrated by the case of chemical ac- 

 tion, the separate eflfects cease entirely, 

 and are succeeded by phenomena al- 

 together different, and governed by 

 different laws. 



Of these cases the former is by far 

 the more frequent, and this case it is 

 which, for the most part, eludes the 

 grasp of our experimental methods. 

 The other and exceptional case is 

 essentially amenable to them. When 

 the laws of the original agents ceaso 

 entirely, and a phenomenon makes its 

 appearance, which, with reference to 

 those laws, is quite heterogeneous ; 

 when, for example, two gaseous sub- 

 stances, hydrogen and oxygen, on 

 being brought together, throw off 

 their peculiar properties, and produce 

 the substance called water — in such 

 cases the new fact may be subjected 

 to experimental inquiry, like any 

 other phenomenon ; and the elements 

 which are said to compose it may be 

 considered as the mere agents of its 

 production ; the conditions on which 

 it depends, the facts which make up 

 its cause. 



The effects of the new phenomenon, 

 the properties of water, for instance, 

 are as easily found by experiment as 

 the eflfects of any other cause. But 

 to discover the cause of it, that is, the 

 particular conjunction of agents from 

 which it results, is often difficult 

 enough. In the first place, the origin 

 and actual production of the pheno- 

 menon are most frequently inacces- 

 sible to our observation. If we 

 could not have learned the composi- 

 tion of water until we found instances 

 in which it was actually produced 



