392 PHILOSOPHICAL THOUGHT. 



substances and affinities or with the instincts and im- 

 pulses visible in organic nature, there remain dark 

 points into which the daylight of exact science has not 

 yet penetrated, relations which are not yet accessible to 

 strict definition in terms of measurable quantities. 



In the seventh chapter of the first portion of this 

 History I have shown how the conception of energy has 

 been gradually evolved out of vaguer conceptions, and 

 how the two principles of the conservation and the 

 dissipation (degradation or disgregation) of energy have 

 56. been established which respectively maintain that the 



Conception 4 . . 



of energy, amount of energy in the physical world remains con- 

 stant, and that this amount tends to change from a 

 more to a less available or useful condition. It was 

 shown how the experimental proofs of the conservation 

 of energy were furnished mainly in England, the 

 theoretical in Germany ; how the idea of dissipation 

 originated in France ; and how the whole doctrine of 

 energy, so far as mechanical processes are concerned, 

 was brought into clear relief and mathematically 

 formulated mainly by the experimental and theoretical 

 labours of Lord Kelvin. At the same time I showed 

 how a school of natural philosophers has arisen in 

 Germany who see in the theory of energy, or energetics, 

 the fundamental doctrine which is to explain all physical 

 phenomena. Unfortunately, so far as philosophical 

 writers are concerned, almost the whole literature down 

 to quite recent times is permeated and vitiated by a 

 want of clear distinction between the mechanical defini- 

 tion of the older term force, which is now superseded by 

 the less ambiguous term energy, and the still prevailing 



