ON THE PHYSICAL VIEW OF NATURE. 119 



to another where it is lower, . . . The production of 

 moving force is therefore due in steam-engines, not to a 

 real consumption of caloric, Ijut to a transference from a 

 hot body to a cold body." ^ 



If it is the object of physical science to describe the 

 processes of nature completely and in the simplest 

 language, we have here an instance of a description of 

 a very general property in very simple language, and in 

 terms which reduce it to a measurable quantity. With- 

 out this, progress is impossible. It is not likely, how- 

 ever, that Carnot saw the full significance of his simple i:. 



Camot 



statement, how in it he had introduced into physical and introduces 



' ^ "^ the idea of 



mathematical science the great question of the avail- abjl'^y'.. 

 ability of the forces of nature, as Mohr and ]\Iayer in 

 (Germany, and Faraday and Grove in England, somewhat 

 later, dwelt on the correlation or interchangeability of 

 those forces. The two ideas were separately developed. 

 When they came together in one mind, when Thomson 

 fully realised the importance and meaning of Ijoth 

 — as he undoubtedly did earlier than any other 

 natural philosopher — he at once established the great 

 doctrine of the dissipation, also called degradation or is. 



. Tliomson iii- 



depreciation, of energy, Jnit it required some modih- tr.Kiuctsihe 

 cation of Carnot's enunciation of this general property '^'pation." 

 before it could be put into its modern form. This 

 modification was preparing itself in Carnot's own mind, 

 as his papers, posthumously puljlished, have revealed 

 to US.2 What required to be modified was the word 



1 Carnot, ' Puissance motrice,' ed. 187S, p. <J0) : " Loi^iiu'une 



ed. 1878, pp. 5 and 6. liypothose ne suffit plus a I'explica- 



* His notebook contained the fol- tion des phc^uom^ne8, elle doit etre 



lowing entry {'Puissance motrice,' abandonnoe. C'est le aw oil ee 



