METHOD OF DISCOVERING CAUSAL LAWS 195 



weight of the condensing tube [T^ + S] from its final weight 

 [T&quot; 2 + S + W~\ we learn how much water is produced ; the quantity 

 of oxygen [O] in it is found by subtracting the final weight of the 

 oxide of copper \C - O] from its original weight [C]. If we then 

 subtract the weight of the oxygen [O] from that of the water [ W\ 

 we learn the weight of the hydrogen [//] which we have combined 

 with the oxygen [O], When the experiment is very carefully 

 performed, as described in Dr. Roscoe s Lessons in Elementary 

 Chemistry (p. 38), we find that 88*89 parts by weight of oxygen 

 unite with n-ii parts by weight of hydrogen to form 100 parts 

 of water.&quot; Thus we have : 



Total weight (initial stage) ^[T 1 + C] + [7 2 + S] 



(final stage) = [T l + C - 0] + [T* + S + W] 

 Therefore the difference [ W - O] must represent the added hydro 

 gen [//]. That is to say, we know how to account for the total 

 weight at the initial stage ; we then add one single antecedent, 

 namely hydrogen ; therefore the excess of the final weight over 

 the initial weight must be due to the added hydrogen. From 

 this we can understand why the present method has been de 

 scribed as a peculiar application of the method of difference. 



It will also enable us to understand why the method is ap 

 plicable only to a homogeneous intermixture of the effects of several 

 co-operating causes, or to some homogeneous aspect of these effects, 

 such as weight in the example given. Obviously, it is only when 

 several causes act at once, and when we have before u the 

 complex resulting effect of their co-operation, that the method 

 can be used at all. But we have to distinguish two ways in which 

 a number of causes may co-operate in the production of a total 

 effect. This latter may be either of the same kind as the effects 

 of the single causes acting separately would be ; or it may be of 

 a different kind from the single effects. In other words, any 

 CONJUNCTION OF CAUSES,&quot;/.*, joint action, simultaneous co 

 operation, of a number of causes, may be either a simple adding 

 together of these causes, a &quot; COMPOSITION OF CAUSES,&quot; to pro 

 duce a &quot; HOMOGENEOUS INTERMIXTURE OF EFFECTS&quot; ; or it may 

 be a mutually modified co-operation of these causes, a &quot; COM 

 BINATION OF CAUSES,&quot; to produce a &quot; HETEROGENEOUS or 

 HETEROPATHIC INTERMIXTURE OF EFFECTS &quot;. Chemical changes, 

 for instance, are heterogeneous or heteropathic effects of the combin 

 ing agencies which produce them. On the other hand, &quot; if in 

 one experiment friction, combustion, compression, and electric 



13* 



