THE DOCTRINE OP ENERGY 85 



scientific reasoning, an implicit reference to Reality, 

 and it facilitates, therefore, the expression of 

 scientific reasoning, when the account of a physical 

 process is stated with reference to a supposed 

 reality, such as Matter. And in making such 

 reference Science is thinking of the thing-in-itself. 

 It is a reference beyond phenomena. 



Heat, Light, Sound, Force, are names of classes of 

 phenomena, and the great discovery of Physics 

 during the nineteenth century has been that these 

 > are all transformable into each other, and bear 

 ' definite numerical relations to each other in pro- 

 portion to which such transformations take place. 

 Science availing itself of this discovery, unifies its 

 conception of Nature and gives expression to 

 the doctrine of the inter-transmutability of the 

 various classes of physical phenomena by postu- 

 ' lating an entity called Energy, and regarding the 

 various classes of phenomena as transmutations 

 which this entity undergoes. But Science has 

 been reluctant to recognise that it is now entitled 

 to dispense with the postulation of Matter. The 

 theory, as announced by the leading men of science, 

 has therefore been to the effect that there exist 

 in the physical universe two real things Matter 

 and Energy in place of one only, as commonly 

 supposed for so long. 



