t64 broomall : thermodynamics of elastic bodies. 



the system or out of it, is a matter of iiiclifference, provided 

 the heat engine is properly arranged to take advantage of the 

 heat flow. If operations are started with systems S and R at 

 the same temperature, and the initial step be that of cooling, 

 there occurs in case S an actual increase of potential energy, 

 despite the fact that heat has been abstracted from the system. 

 The heat abstracted is that due to the fall of temperature, less 

 that corresponding to raising the weight. As a matter of fact 

 both systems S and R have less total energy at the end of the 

 cooling process than before. When system S is again heated 

 to the original temperature the weight falls, and the transfer 

 of heat to the system is that necessary to raise the tempera- 

 ture, less the heat equivalent of the falling weight. 



The action of system R with cooling as the first step, is 

 evident without comment. 



It is interesting to note that the action of the spiral spring 

 with cooling as the first step, is somewhat on a par with the 

 mechanical force which bursts a water pipe on freezing. In 

 this case we have a flow of heat away from the water doing 

 the work of breaking the pipe. Another somewhat similar 

 example is the additional energy obtained in a steam engine 

 by condensing the exhaust steam. 



In all these actions it is not that the total energy of the 

 system is increased by taking heat from it, but only that by 

 cooling a flow of heat is caused to take place which does 

 mechanical work in the heat engine, be it spiral spring, freez- 

 iny water or steam engine. 



