A HISTORY OF SCIENCE 



of the doctrine of universal gravitation? The judg- 

 ment of posterity is unjust, but it is inexorable. And 

 so we can little doubt that a century from now one 

 name will be mentioned as that of the originator of the 

 great doctrine of the conservation of energy. The man 

 whose name is thus remembered will perhaps be spoken 

 of as the Galileo, the Newton, of the nineteenth cen- 

 tury ; but whether the name thus dignified by the final 

 verdict of history will be that of Colding, Mohr, Mayer, 

 Helmholtz, or Joule, is not as yet decided. 



LORD KELVIN AND THE DISSIPATION OF ENERGY 



The gradual permeation of the field by the great 

 doctrine of conservation simply repeated the history 

 of the introduction of every novel and revolutionary 

 thought. Necessarily the elder generation, to whom 

 all forms of energy were imponderable fluids, must pass 

 away before the new conception could claim the field. 

 Even the word energy, though Young had introduced 

 it in 1807, did not come into general use till some time 

 after the middle of the century. To the generality of 

 philosophers (the word physicist was even less in favor 

 at this time) the various forms of energy were still 

 subtile fluids, and never was idea relinquished with 

 greater unwillingness than this. The experiments of 

 Young and Fresnel had convinced a large number of 

 philosophers that light is a vibration and not a sub- 

 stance ; but so great an authority as Biot clung to the 

 old emission idea to the end of his life, in 1862, and held 

 a following. 



Meantime, however, the company of brilliant young 

 men who had just served their apprenticeship when the 



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