86 THE PROGRESS OF S( IT.M K n 



mechanical work. Thus originated the mechanical 

 theory of heat, which became the starting point of 

 the modern doctrine of the conservation of energy. 

 Molar motion had appeared to be destroyed 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 

 molecular motion, or motion of the smallest par- 

 ticles of a body, which constitutes heat. The loss 

 of the masses is the gain of their particles. 



Before 1843, however, the doctrine of the con- 

 servation of energy had been approached. Bacon's 

 chief contribution to positive science is the happy 

 guess (for the context shows that it was little 

 more) that heat may be a mode of motion ; Des- 

 cartes affirmed the quantity of motion in the 

 world to be constant ; Newton nearly gave expres- 

 sion to the complete theorem ; while Rumford's and 

 Davy's experiments suggested, though they did 

 not prove, the equivalency of mechanical and 

 thermal energy. Again, the discovery of voltaic 

 electricity, and the marvellous development of 

 knowledge, in that field, effected by such men as 

 Davy, Faraday, Oersted, Ampere, and Melloni, 

 had brought to light a number of facts which 

 tended to show that the so-called " forces " at work 

 in light, heat, electricity, and magnetism, in 

 chemical and in mechanical operations, were in- 

 timately, and, in various cases, quantitatively! 

 related. It was demonstrated that any one could 



