HERMANN VON HELMHOLTZ 



forces of nature supplied to it from the outer world ? 

 Was the living body, in short, only a minute portion 

 of the mechanism of the cosmos ; or was there some- 

 thing beyond, some spiritual fuel continually being 

 added to its vital fires ? Helmholtz thought that if 

 the life was fed from some such source of external 

 energy, then the living body was an example of a 

 perpetuum mobile, a perpetual motion, an idea he had 

 often heard ridiculed in the philosophical discussions 

 that were not infrequent in his father's home. 



If, again, the natural forces were found competent 

 to explain the phenomena of life without the assump- 

 tion of a vital force, how were these forces related to 

 each other ? About this period Helmholtz filled the 

 humble office of assistant in the library of the Friedrich 

 Wilhelm Institute, and in what he modestly terms 

 his ' idle moments,' he had read the works of Euler, 

 Daniel Bernoulli, d'Alembert, and other mathe- 

 maticians of the eighteenth century, no mean in- 

 dication of his mathematical powers, and he thus 

 became equipped for the discussion of the great 

 question. He was especially acquainted with the 

 manifold applications made by Daniel Bernoulli, of 

 Leibnitz's idea of vis viva. 



Such considerations led Helmholtz, in his twenty- 

 sixth year, to write his famous essay, Ueber die Erhaltung 

 der Kraft on the Conservation of Force one of the 

 epoch-making scientific papers of the century. Clerk 

 Maxwell has well said : ' To appreciate the full 

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