130 SCIENTIFIC THOUGHT. 



equivalence and correlation of forces, such as Faraday,, 

 Mohr, Mayer, Grove — not even Joule and Helmholtz — 

 that if neither matter nor power is lost, the phenomena 

 of loss and waste in nature and in human life remain 

 unexplained. The only mind to whom this problem 

 presented itself was Sadi Carnot, and it presented itself 

 to him in an extreme form ; for he started with the 

 idea that even heat itself in doing work was not lost 

 or destroyed, but handed over from the hotter body 

 (the boiler of the steam-engine) to the colder body (the 

 condenser of the steam-engine). We now know that 

 this view was not correct — that the whole heat is not 

 handed over, but always only a portion of the heat. But,, 

 with this exaggerated view in his mind, he tried to explain 

 the phenomena of loss and waste, and he conceived that 

 the explanation lay in the lowering of the temperature. 

 " It would be difficult to say why " — though he had 

 assumed it as an axiom that — " in the development of 

 motive power by heat, a cold body should be necessary, 

 why in consuming the heat of a heated body we cannot 

 produce motion." ^ Heat at high temperature is of more- 

 value for doing work than the same amount of heat at 



^ The words quoted are taken 

 from cue of the fragments published 

 in the year 1878 by H. Carnot from 

 the posthumous MSS. of his brother, 

 Sadi Carnot. In this fragment he 

 approaches the modern conception 

 that heat is the result of motion : 

 he sees that all other phenomena 

 can be explained by this hypothesis ; 

 but he pauses after having stated 

 the difficulty quoted above in the 

 text, and reverts, after some 

 further queries, to the same diffi- 



culty in the words, ' ' Can one con- 

 sume the heat entirely without 

 letting any arrive at the body B 

 [viz., from a body A] ? If this were 

 possible, one could create motive 

 power without consumption of fuel, 

 and simply by the destruction of 

 the heat of bodies" ('Puissance 

 motrice, &c. ,' ed. 1878, pp. 92 and 

 94). It is interesting to see how 

 nearly these reflections approach to 

 those made more than twenty years 

 later by Thomson. 



