THE STORY OF NINETEENTfl-CRNTUKY SCIENCE 



A vast generalization such as this is never a mush- 

 room growth, nor does it usually spring full grown from 

 the mind of any single man. Always a number of 

 minds are very near a truth before any one mind fully 

 grasps it. Pre-eminently true is this of the doctrine of 

 conservation of energy. Not Faraday alone, but half a 

 dozen different men had an inkling of it before it gained 

 full expression; indeed, every man who advocated the 

 undulatory theory of light and heat was verging towards 

 the goal. The doctrine of Young and Fresnel was as a 

 highway leading surely on to the wide plain of conser- 

 vation. The phenomena of electro-magnetism furnished 

 another such highway. But there was yet another road 

 which led just as surely and even more readily to the 

 same goal. This was the road furnished by the phe- 

 nomena of heat, and the men who travelled it were des- 

 tined to outstrip their fello w- workers ; though, as we 

 have seen, wayfarers on other roads were within hailing 

 distance when the leaders passed the mark. 



In order to do even approximate justice to the men 

 who entered into the great achievement, we must recall 

 that just at the close of the last century Count Rumford 

 and Humphry Davy independently showed that labor 

 may be transformed into heat ; and correctly interpreted 

 this fact as meaning the transformation of molar into 

 molecular motion. We can hardly doubt that each of 

 these men of genius realized, vaguely, at any rate, that 

 there must be a 'close correspondence between the 

 amount of the molar and the molecular motions; hence 

 that each of them was in sight of the law of the me- 

 chanical equivalent of heat. But neither of them quite 

 grasped or explicitly stated what each must vaguely 

 have seen ; and for just a quarter of a century no one 



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