374 THE PHILOSOPHY OF BIOLOGY 



a certain fraction of the heat received to the refriger- 



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at or a fraction equal to @ t =L, it gives up rather 



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more, because it is not a perfect mechanism, that is, it 

 generates friction, etc. Some of the heat received 

 thus ceases to be available for the performance of 

 work, and passes into the refrigerator. The fraction 

 of the heat-energy which passes into the refrigerator 

 in the perfectly reversible engine was unavailable 

 energy in the conditions in which the mechanism 

 worked, or was imagined to work, but in the actual 

 engine this fraction is increased. If we divide the 

 increase of unavailable energy by the temperature of 

 the refrigerator, the product is the increase of entropy 

 generated in the actual engine over that generated 

 in the ideal engine. Because of this reduction of 

 available energy the actual engine is an irreversible 

 mechanism. 



This is the connection between unavailable energy 

 and entropy. In all transformations some fraction 

 of the transforming energy becomes heat, and this 

 heat flows by conduction and radiation into the sur- 

 rounding bodies. In general this heat simply raises 

 the temperature of the medium into which it flows, 

 and becomes unavailable for further transformations. 

 With every transformation that occurs some part of 

 the energy involved becomes unavailable. Therefore 

 although the sum of the available and unavailable 

 energy of the Universe remains constant, the fraction of 

 unavailable energy tends continually to a maximum. 



INERT MATTER 



We can see now what is indicated by Bergson's 

 " inert matter." It is not matter deprived of energy 



