ON THE DISSIPATION OF ENERGY. 459 



" is a motion among the particles of bodies. 

 " Wherever there is destruction of motive power 

 " there is at the same time production of heat in 

 " quantities precisely proportional to the quantity 

 " of motive power destroyed. Conversely wherever 

 " there is destruction of heat there is production 

 " of motive power. 



" We may then assert the general proposition 

 "that motive power is of invariable amount in 

 " nature ; that it can never, properly speaking, be 

 " said to be either produced or destroyed. In 

 "truth, it experiences changes of form, that is to 

 " say, it produces sometimes one kind of movement, 

 " and sometimes another, but it is never annulled." 



These words contain a perfectly clear and 

 general statement of the " Conservation of 

 Energy ; " but Carnot did not live long enough 

 to see how his original doctrine of the motive 

 power of fire was to be reconciled to this principle. 

 He says (p. 92) : 



" It would be difficult to say why, in the develop- 

 " ment of motive power by consuming the heat of 

 " a hot body, a cold body is necessary ; or why we 



