42 PKOOKES8 : ITS LAW AND CAUSE. 



deal, the causes arc more or less compound ; as indeed arc 

 nearly all causes with which we arc acquainted. Scarcel) 

 any change can with logical accuracy be wholly ascribed to 

 one agency, to the neglect of the permanent or temporary 

 conditions under which only this agency produces the 

 change. But as it docs not materially affect our argument, 

 we prefer, for simplicity s sake, to use throughout the popu 

 lar mode of expression. 



Perhaps it will be further objected, that to assign loss 

 of heat as the cause of any changes, is to attribute these 

 changes not to a force, but to the absence of a force. And 

 this is true. Strictly speaking, the changes should be at 

 tributed to those forces which come into action when the 

 antagonist force is withdrawn. But though there is an in 

 accuracy in saying that the freezing of water is due to the 

 loss of its heat, no practical error arises from it ; nor will 

 a parallel laxity of expression vitiate our statements respect 

 ing the multiplication of effects. Indeed, the objection 

 serves but to draw attention to the fact, that not only does 

 the exertion of a force produce more than one change, but 

 the withdrawal of a force produces more than one change. 

 And this suggests that perhaps the most correct statement 

 of our general principle would be its most abstract state 

 ment every change is followed by more than one othei 

 change. 



Returning to the thread of our exposition, we have next 

 to trace out, in organic progress, this same all-pervading 

 principle. And here, where the evolution of the homoge 

 neous into the heterogeneous was first observed, the produc 

 tion of many changes by one cause is least easy to demon 

 strate. The development of a seed into a plant, or an 

 ovum into an animal, is so gradual, while the forces which 

 determine it arc so involved, and at the same time so unob 

 trusive, that it is difficult to detect the multiplication of effects 

 which is elsewhere so obvious. Nevertheless, guided by 



