A HISTORY OF SCIENCE 



preaching the same truth along another path, to point 

 out its full significance. 



The great generalization which Faraday so narrowly 

 missed is the truth which since then has become fa- 

 miliar as the doctrine of the conservation of energy the 

 law that in transforming energy from one condition to 

 another we can never secure more than an equivalent 

 quantity; that, in short, "to create or annihilate ener- 

 gy is as impossible as to create or annihilate matter; 

 and that all the phenomena of the material universe 

 consist in transformations of energy alone. ' ' Some phi- 

 losophers think this the greatest generalization ever 

 conceived by the mind of man. Be that as it may, it is 

 surely one of the great intellectual landmarks of the 

 nineteenth century. It stands apart, so stupendous 

 and so far-reaching in its implications that the genera- 

 tion which first saw the law developed could little ap- 

 preciate it; only now, through the vista of half a cen- 

 tury, do we begin to see it in its true proportions. 



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 

 the 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 ad- 

 vocated 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 conservation. The phenomena of electro- 

 magnetism furnished another such highway. But there 



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