THE INDIRECT JUSTIFICATION OF ENTELECHY 163 



that " work," that is to say the amount of one of the two kinds 

 of energy in mechanics, has been accepted as a standard 

 measurement of energy in general. But that in thermo- 

 dynamics the so-called quantity of heat must be measured 

 by " ergs " and not temperature, is a real empirical fact. 

 In general terms we may say that the general form of the 

 principle of conservation is aprioristic, though its special 

 content, regarding the kind of quantity to be measured by 

 ergs, is empirical, pure mechanics excepted. 



All these relations seem to be very simple. In short : 



m 

 a body in motion endowed with the kinetic energy v* 



a 



may perform a specific amount of work pi, that is to say, 

 may overcome the force p along the distance I, and, on the 

 other hand, the force p affecting the body along the dis- 



171 



tance I will impart to it the kinetic energy v 2 again ; 



Zt 



and one so-called calorie is always " equivalent ' : to 424 

 kilogrammetres. 



But things are far from being as simple as they seem 

 at the first glance. The law of the conservation of energy 

 is far from being empirically true if only those natural 

 agents which are actually measurable as performing work 

 are taken into consideration. But the truth of our 

 principle is postulated by reason, and therefore the empirical 

 incorrectness of the principle is corrected in a very interest- 

 ing way. Whenever the principle fails to hold, so-called 

 " potential energies " are postulated, into which actual 

 energy may disappear or from which it may originate. 

 Such potential energies play their role in the theories of 

 gravitation, of electricity, elasticity, and some other branches 



