470 M. Vcrdet's Historic Notice of 



which I have first spoken. It has not perhaps been demonstrated 

 in a single case, says Young in his ' Lecture on the Measure- 

 ment and Nature of Heat/ that the quantity of heat absorbed in 

 any phenomenon is precisely equal to the heat disengaged when the 

 phenomenon is inverted. In this simple doubt was virtually con- 

 tained the whole mechanical theory of heat*. 



Unhappily this was an epoch in which the law of double refrac- 

 tion was considered as an argument in favour of the theory of 

 emission ; it was the epoch when the most beautiful memoirs of 

 Fresnel remained forgotten, and for years ran the risk of being 

 lost. Thus when in 1824 the original mind of Sadi Carnot, 

 struck by the spectacle of the industrial revolution accomplished 

 by the steam-engine, sought to discover the general laws of the 

 motive power of fire, he did not hesitate for an instant to take 

 as the point of departure for his reasonings the materiality, and 

 consequently the indestructibility of caloric f- I shall perhaps 

 astonish you if I add that, in spite of this fundamental mistake, 

 the name of Sadi Carnot and that of his learned commentator 

 M. Clapeyron, will always occupy an important place in the 

 history of the science. Sadi Carnot is the author of the forms 

 of reasoning employed incessantly in the mechanical theory ; it 

 is in his essay that we find the first examples of those cycles of 

 operations which consist in taking a body in a certain state, 

 causing it to pass to a different one by following a certain path, 

 and then causing it to return by a different route to its first con- 

 dition. M. Clapeyron has cleared up what remained obscure in 

 the memoir of Carnot, and has shown how we may translate 

 analytically, and represent geometrically, this mode of reasoning, 

 so new and so fruitful J. These two geometers have in a manner 

 created the logic of the science. When the veritable principles 

 had been discovered, nothing was necessary but to introduce them 

 into the forms of that logic ; and it may be believed that, without 

 the previous labour of Carnot and Clapeyron, the progress of the 

 new theory would not have been nearly so rapid as it has been. 



Finally, I will terminate this first part of my historic exposi- 

 tion by mentioning that M. Seguin, in a memoir published in 

 1839, and more especially devoted to political economy than to 

 physics, has considered the steam-engine from a point of view 

 which closely resembles the manner in which 1 attempted in our 



* Lectures on Natural Philosophy, vol. i. p. 651 of the edition of 180/. 

 Young admits that the equality of the heat absorbed and the heat liberated 

 is probable ; but the simple utterance of a doubt regarding this sort of axiom 

 in 1807 is very worthy of remark. 



t Reflexions sur la puissance motrice dufeu, et sur les machines propres 

 a developper cette puissance. Paris, 1824. 



X " Memoire sur la puissance motrice de la chaleur " (Journal de VEcole 

 Polytechnique, vol. xiv. annee 1834). [Translated in Taylor's Scientific 

 Memoirs, Part III.] 



