IN THE LAST HALF-CENTUEY. 71 



out, by rubbing them together, was practi- 

 cally illimitable. This result brought phi- 

 losophers face to face with the contradic- 

 tion of supposing that a finite body could 

 contain an infinite quantity of another 

 body ; but it was not until 1843, that Mechan- 

 clear and unquestionable experimental ry of 

 proof was given of the fact that there is a ea * 

 definite relation between mechanical work 

 and heat ; that so much work always 

 gives rise, under the same conditions, to 

 so much heat, and so much heat to so 

 much mechanical work. Thus originated 

 the mechanical theory of heat, which be- 

 came the starting-point of the modern 

 doctrine of the conservation of energy. 

 Molar motion had appeared to be de- 

 stroyed by friction. It was proved that 

 no destruction took place, but that an 

 exact equivalent of the energy of the lost 

 molar motion appears as that of the mo- 

 lecular motion, or motion of the smallest 

 particles of a body, which constitutes 



