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, but to a transference from a 

 hot body to a cold body." 1 



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 IT. 



r Carnot 



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



r J the idea of 



mathematical science the great question of the avail- ability"" 

 ability of the forces of nature, as Mohr and Mayer 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 both 

 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. 



. . Thomson iu- 



depreciation. 01 energy. But it required some modin- troducesthe 



idea of "dis- 



cation of Carnot's enunciation of this general property 

 before it could be put into its modern form. This 

 modification was preparing itself in Carnot's own mind, 

 as his papers, posthumously published, have revealed 

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



1 Carnot, ' Puissance motrice,' ed. 1878, p. 90) : " Lorsqu'une 

 ed. 1878, pp. 5 and 6. j hypothec ne suffit plus a 1'explica- 



2 His notebook contained the fol- tion des phe'nomenes, elle doit etre 

 lowing entry (' Puissance motrice,' abandonne"e. C'est le cas ou se 



