46 MOTIVE POWER OF HEAT. 



least partially, for on the one hand the heated air, 

 after having performed its function, having passed 

 round the boiler, goes out through the chimney 

 with a temperature much below that which it had 

 acquired as the effect of combustion; and on the 

 other hand, the water of the condenser, after hav- 

 ing liquefied the steam, leaves the machine with 

 a temperature higher than that with which it 

 entered. 



The production of motive power is then due in 

 steam-engines not to an actual consumption of 

 caloric, but to its transportation from a warm 

 body to a cold body, that is, to its re-establishment 

 of equilibrium an equilibrium considered as de- 

 stroyed by any cause whatever, by chemical action 

 such as combustion, or by any other. We shall 

 see shortly that this principle is applicable to 

 any machine set in motion by heat. 



According to this principle, the production of 

 heat alone is not sufficient to give birth to the 

 impelling power: it is necessary that there should 

 also be cold; without it, the heat would be use- 

 less. And in fact, if we should find about us 

 only bodies as hot as our furnaces, how can we 

 condense steam ? What should we do with it if 

 once produced ? We should not presume that we 

 might discharge it into the atmosphere, as is done 



