ON THE PHYSICAL VIEW OF NATUEE. 123 



foundations on which the theory of heat rests require 

 careful examination. 1 Further thought evidently led 

 him to doubt the correctness of the second assumption. 

 It is the first point to which Thomson, more than 

 twenty years after, directs his attention. He conceives 

 the idea of measuring temperature by such a scale that 

 for an equal drop in the scale i.e., by letting down heat 

 by an equal number of degrees on the new scale equal 

 amounts of work shall be done. 2 The speculations of Sadi 

 Carnot remained unnoticed for a long time. Ten years 21. 



o . Clapeyron's 



later Clapeyron reverted to the subject, and put the graphical 



method. 



reflections of Carnot into graphical form and into mathe- 

 matical language. He introduced the conception, based 

 on Carnot's theory, of the ratio of heat transferred from 

 a higher to a lower level of temperature to the maxi- 

 mum of work obtainable, a quantity independent of 

 the substance employed, and he called this fixed ratio 

 Carnot's function. It was through his paper that 



motrice est . . . due . . . non a i himself from the conventional or 

 une consommation re"elle du cal- I material view of the nature of 



orique, inais h son transport d'un 

 corps chaud a un corps froid, c'est- 

 a-dire a son rdtablissement d'equi- 

 libre" (ibid., p. 6). 



1 " Au reste, pour le dire en 

 passant, les principaux fondements 

 sur lesquelles repose la theorie de 



heat. See the appendix to the 

 edition of 1878. 



2 See ' Cambridge Philosophical 

 Society Proceedings,' June 1848 ; 

 reprinted in Thomson's (Lord Kel- 

 vin's) ' Math, and Phys. Papers,' 

 vol. i. p. 100. 



la chaleur auraient besoin de 1'ex- i s Benoit Pierre fiinile Clapeyron 



amen le plus attentif. Plusieurs was an engineer. In 1834 he pub- 



faits d'experience paraissent a peu lished, in the fourteenth cahier of 



pres inexplicables dans 1'etat actuel the ' Journal de 1'Ecole Polytech- 



de cette theorie" (ibid., p. 20, nique,' his "Me'moire sur la Puis- 



note). "La loi fondamentale que sance motrice de la Chaleur." It 



nous avions en vue . . . est assise was through a translation of this 



sur la theorie de la chaleur telle paper in ' Taylor's Scientific Mem- 



qu'on la con^oit aujourd'hui, et il oirs ' that Thomson heard about 



faut 1'avouer, cette base ne nous Carnot's earlier work, and through 



parait pas d'une solidit^ ine'bran- a translation in Poggendorf's 'An- 



lable" (p. 50). As stated above nalen ' (1843) that Helmholtz be- 



(p. 118, note), Carnot emancipated came acquainted with the subject. 



