ON THE PHYSICAL VIEW OF NATURE. 



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 

 later Clapeyron 3 reverted to the subject, and put the 

 reflections of Carnot into graphical form and into mathe- 

 matical language. He introduced the conception, based 

 on Garnet'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 



21. 



Clapeyron's 



graphical 



method. 



motrice est . . . due . . . non a 

 une consommation re"elle du cal- 

 orique, mais a son transport d'un 

 corps chaud a un corps froid, c'est- 

 a-dire a son re'tablissement d'e'qui- 

 libre" (ibid., p. 6). 



1 " Au reste, pour le dire en 

 passant, les principaux fondements 

 sur lesquelles repose la the'orie de 

 la chaleur auraient besoin de 1'ex- 

 &men le plus attentif. Plusieurs 

 faits d'expe"rience paraissent a peu 

 pres inexplicables dans I'e'tat actuel 

 de cette the'orie" (ibid., p. 20, 

 note). " La loi fondamentale que 

 nous avions en vue . . . est assise 

 sur la the'orie de la chaleur telle 

 qu'on la con9oit aujourd'hui, et il 

 faut 1'avouer, cette base ne nous 

 parait pas d'une solidite" ine"bran- 

 lable" (p. 50). As stated above 

 {p. 118, note), Carnot emancipated 



himself from the conventional or 

 material view of the nature of 

 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. 



3 Benoit Pierre Emile Clapeyron 

 was an engineer. In 1834 he pub- 

 lished, in the fourteenth cahier of 

 the ' Journal de 1'Ecole Polytech- 

 nique,' his " Mdmoire sur la Puis- 

 sance motrice de la Chaleur." It 

 was through a translation of this 

 paper in ' Taylor's Scientific Mem- 

 oirs ' that Thomson heard about 

 Carnot's earlier work, and through 

 a translation in Poggendorf's 'An- 

 nalen' (1843) that Helmholtz be- 

 came acquainted with the subject. 



