278 



HEAT. 



meet it, the mass being such that the total potential energy remained 

 unchanged, or if we could imagine an electrical system in which the work 

 gained by passage to a lower potential turned some machine, increasing 

 the charges at the lower potential so that the total electrical energy 

 remained unchanged, we should have cases analogous to the conduction 

 of heat. 



The difference really turns on the fact that entropy tends to increase, 

 while its analogues, mass and quantity of charge, are constant. 



Dissipation or Degradation of Energy. Through conduction 



and radiation there is a continual tendency to reduce differences of 

 temperature in the universe, and therefore to reduce the amount of heat 

 available for transformation. Though not diminishing, but on the 

 contrary increasing in amount, the heat is continually approximating 

 more to a dead level, being " degraded " or " dissipated." The quantity 

 of other forms of energy available for transformation is also diminishing, 



FlG. 159. Intriusic Energy. 



for in every transformation which occurs some heat is generated, and this 

 can never be wholly retransformed. 



There is, as it were, a tax levied on every transformation, the proceeds 

 being put into an untransformable fund. The amount of possible trans- 

 formation by any method which we can at present conceive is therefore 

 gradually diminishing, a fact which is expressed by saying that the 

 energy is undergoing dissipation or degradation. More and more, 

 energy is assuming the form of heat, which may be regarded as the 

 stable form, and a dead level of temperature is the state which we are 

 gradually approaching. 



Intrinsic Energy. The energy which a substance possesses in 

 itself is termed its intrinsic or internal energy. We have no means of 

 measuring the total quantity of a body's intrinsic energy, but we can 

 find the amount added in changing from one condition to another. 



It will obviously be the amount of heat added less the external work 

 done. We may give some attempt at representation on the indicator 

 diagram. Let AB (Fig. 159) be the curve representing the change from 

 the condition A to the condition B Draw the adiabatics Aa, B/3, down to 



