THE CONSERVATION OF ENERGY 



ticular case within a more general law. If heat cannot 

 be in any sense created, but only made manifest as a 

 transformation of another kind of motion, then must 

 not the same thing be true of all those other forms of 

 "force" -light, electricity, magnetism which had 

 been shown to be so closely associated, so mutually con- 

 vertible, with heat? All analogy seemed to urge the 

 truth of this inference; all experiment tended to con- 

 firm it. The law of the mechanical equivalent of heat 

 then became the main corner-stone of the greater law 

 of the conservation of energy. 



But while this citation is fresh in mind, we must turn 

 our attention with all haste to a country across the 

 Channel to Denmark, in short and learn that even 

 as Joule experimented with the transformation of heat, 

 a philosopher of Copenhagen, Colding by name, had 

 hit upon the same idea, and carried it far towards a de- 

 monstration. And then, without pausing, we must 

 shift yet again, this time to Germany, and consider the 

 work of three other men, who independently were on 

 the track of the same truth, and two of whom, it must 

 be admitted, reached it earlier than either Joule or 

 Colding, if neither brought it to quite so clear a de- 

 monstration. The names of these three Germans are 

 M<>hr, Mayer, and Helmholtz. Their share in estab- 

 lishing the great doctrine of conservation must now 

 claim our attention. 



As to Karl Fried rich Mohr, it may be said that his 

 statement of the doctrine preceded that of any of his 

 fellows, yet that otherwise it was perhaps least imp- >r- 

 tant. In 1837 this thoughtful German had grasped 

 the main truth, and given it expression in an article 



257 



