Place of 8((di Carnot in the Hidory of Thermotics. 19 

 II. — Tlie Place of Sadi Carnot in the History of Thermotics. 



BY PROF. B. H. THURSTOK. 

 Read April 5th. 1880. 



M. Ilirscli, ill liis Introduction to liis translation of the 

 writer's History of the Steam Engine,* publishes a new fact 

 relating to Carnot and the history of the mechanical theory of 

 heat, as revealed in recently discovered documents, which had 

 only come to his knowledge at the time of writing. 



The documents referred to, were presented to the President 

 of the Academy of Sciences by M. H. Carnot, November SOtli, 

 1878. They show clearly, that if the doctrine of the equiva- 

 lence of heat and mechanical energy was not recognized by 

 Sadi Carnot when, in 1824, he published his now celebrated 

 work, ^^ Reflexions sur la Puissance llotive clu Feu," the idea 

 of the identity of the two forms of energy soon did become 

 recognized by him and observable in the course of his work. 



The following are extracts from the manuscript notes left by 

 Carnot : — 



''LaChaleur n'est autre que la puissance motive, on plutot, 

 que le mouvement qui a change de forme. C'est un mouvement 

 dans les particules des corps. Partout on il y a destruction de 

 puissance motive, il y a, en meme temps, production de chaleur 

 en quantite precisemcnt proportionelle a la quantite de puissance 

 motive detruite. Reciproquement, partout oil il y a destruction 

 de chaleur, il y a production de puissance motive." 



"On pent done poser en these generale que la puissance 

 motive est en quantite invariable dans la nature, qu'elle n'est 

 jamais, a proprement parler, detruite. A la verite, elle change 

 de forme, c'est-a-dire qu'elle produit tantot un genre de mouve- 

 ment, tantot un autre ; mais jamais elle n'est aneantie." 



[Heat is nothing else than motive power (energy), or rather, 

 a motion which has changed its form. It is a motion of the 

 molecules of bodies. Whenever motive power is destroyed, there 

 is, at the same time, a production of heat in quantity precisely 

 proportional to the quantity of power destroyed. Reciprocally, 



* Histoire de la Machine a Vapeur, par R. H. Thurston, Prof, of Mechanical Engineering 

 at the Stevens Institute cf Technology. Revised, annotated and enlarged by J. Hirsch, Prof, 

 of the Steam Engine at " Ecole des Ponts et Chaussees de Paris ;" — Vol. I, p. XV, foot note. 



