i6 PHYSICAL SCIENCE 



department and the prevalent direction of inquiry, 

 while new divisions may spring into existence. 



The different sciences are not even parts 

 of a whole ; they are but different aspects of 

 a whole, which essentially has nothing in it 

 corresponding to the divisions we make ; they 

 are, so to speak, sections of our model of Nature 

 in certain arbitrary planes, cut in directions to 

 suit our convenience. Thus a nerve-impulse 

 may be considered in a psychological aspect, a 

 physiological aspect, or a physical aspect. Even 

 these divisions may be sub-divided ; the physics 

 of the nerve-impulse may be studied first from 

 the electrical side by investigating the electric 

 currents that accompany it, and then from the 

 mechanical side, by correlating the electrical 

 currents with the movements of matter that 

 simultaneously occur. No one of these aspects 

 of the phenomenon is essentially more funda- 

 mental than any other, and the conviction at 

 one time prevalent, and even now by no means 

 uncommon, that a complete mechanical ex- 

 planation of every phenomenon is possible and 

 fundamental, seems merely an unphilosophical 

 fallacy. Its origin is to be sought in the 

 historical fact that the section known as 

 mechanics was the earliest of the physical 

 sciences, and that its methods and conclusions 

 are fairly intelligible to the ordinary man, and, 

 in their elements, essential to his daily life. 

 The science of mechanics has been more fully 

 developed from its experimental basis by the 

 methods of mathematical analysis than any other 

 branch of Natural Knowledge, and mankind has 

 hence come to believe that it is essentially simpler 



