430 ACTUAL WORKING IN ORIGINAL RESEARCH. 



If the phenomenon is due to the concurrent action of 

 several conditions (and* this is a very common case), the 

 exclusion of all of these will entirely prevent it, and the 

 exclusion of one or more of them will either prevent it 

 wholly, or alter its form or amount. 



The determination of the true effects of particular 

 causes is accomplished in a similar manner to the finding 

 of the causes themselves. We can test the effect of a given 

 cause, but not the cause of a given effect ; in the latter 

 case we must first conjecture, or raise an hypothesis of a 

 probable cause, and then test our conjecture. Both the 

 problems are, therefore, solved in the same way. As 

 the different forces of nature act according to more or less 

 different laws, essentially different causes must, under the 

 same conditions, produce more or less different effects ; but 

 as, under different conditions, the same effect may be due 

 to different causes, we cannot safely infer that because a 

 force A is different from a force B, all the effects of A are 

 different from those of B. From the absence of a cause 

 we may infer the absence of the whole of its own peculiar 

 effects, but not of those of its effects which other causes 

 also may produce. If a cause or any number of con- 

 spiring causes produce, either directly or indirectly, an 

 effect or any number of effects, the absence of the causes 

 will be attended by non-production of all the effects. 



In some cases a whole chain or series of phenomena 

 occurs, in which each preceding one is a cause and each suc- 

 ceeding one an effect, and the last of the series is as truly a 

 result of the first as the second one is, but not so imme- 

 diately ; for instance, the last carriage in a railway train is 

 not less certainly drawn by the engine than it is by the 

 carriage next preceding it. Generally, if the real cause or 

 causes of a phenomenon are altered in amount, the quantity 

 of the effect will also be altered. Lapse of time does not 



