20 Place of Scull Carnot in the History of TUermotics. 



wherever there is destruction of heat, there is production of 

 poAver of motion, 



Wc may then state as a general hxw, that energy is, in nature, 

 invariable in amount ; that is, is never, properly speaking, either 

 created or destroyed. In fact, it clianges form ; that is, it causes 

 sometimes one kind of motion, sometimes another ; but it is 

 never destroyed.] 



Again : 



* * * * D'apres quclques idees que je me suis forme sur la 

 tlieoric de la chaleur, la production d'une unite de puissance 

 motive necessite la destruction de 2.70 unites de la chaleur 

 (cluique unite de puissance motive, on dynamic, representant 

 Ic ])oids de 1 metre cube d'eau eleve a 1 metre de hauteur." 



[* * * * According to my ideas of the theory of heat, the 

 production of a unit of energy demands the destruction of 2.70 

 units of heat (each unit of energy, or dynamie, representing the 

 raising of the weight of one cubic meter of water one meter 

 high.] 



This estimate gives for the value of the "mechanical equiva- 

 lent of heat," j^ = 3T0, roughly approximating 424, the metric 

 equivalent of 772 foot-pounds, the British unit of heat-equiva- 

 lence. 



M. liirsch remarks upon the precision with whicli Carnot 

 states t.he laAV of equivalence of heat and work, as well as the 

 more general law of the "conservation of energy." The con- 

 siderations which lead him to this last-named law are of the 

 extremest simplicity. 



Still more : Carnot lays out a complete programme of experi- 

 ments on heat and energy — the very experiments since made by 

 Joule, Thompson, Hirn, Eegnault, and others. 



Hitherto, Carnot has been credited with the invention of the 

 standard method of examination of the relations between heat 

 and work, and it has been assumed that he was, to the last, a 

 believer in the materiality of heat. His idea that we can only 

 infer this relation after studying processes of such nature as 

 present a complete cycle of changes resulting in the perfect 

 restoration of the primitive physical conditions observed in the 

 working substances, and his proposition that the reversible 

 engine is the perfect engine, have admittedly formed the basis 



