112 



SCIENTIFIC THOUGHT. 



viction in that direction. The experimental result did 

 not satisfy Helmholtz, who, about the same time, was 

 led to consider the. origin of animal heat in living 

 organisms, a problem with which Liebig l had been 

 greatly occupied for several years. Without himself 

 devising or instituting new experiments, or attempting 

 any determination of the equivalent as others notably 

 Colding and Holtzmann were doing, Helmholtz, in 

 1847, undertook a theoretical investigation which has 

 since become classical a corner-stone in the philosophy 

 of the subject. He first of all gave the principle in- 

 volved a correct mathematical expression, showed how it 

 could be considered as an extension of the theorem known 

 in abstract dynamics as the conservation of the vis viva 

 of a mechanical system, attempted to define the nature of 

 forces, in the Newtonian sense, which would be subject to 

 the new principle, and brought it into logical connection 

 with the axiom laid down and used by French philos- 

 ophers, that perpetual motion is an impossibility. After 

 clearing the ground so far as abstract dynamics is con- 

 cerned and giving the necessary definitions, sharply dis- 

 tinguishing between acting (living) forces and mere 

 tensions (dead forces), Helmholtz proceeds to draw all 



established according as strict 

 definitions, experimental proofs 

 and figures, and mathematical 

 formulas took the place of vague 

 speculations. Joule did the experi- 

 mental, Helmholtz the mathema- 

 tical, part of the work ; but it is 

 interesting to see how little the 

 latter without the former was able 

 to impress contemporary German 

 writers with the value of the prin- 

 ciple which he established. He 



himself even did not for a long 

 time develop the line of reasoning 

 which he had begun. 



1 See Helmholtz, ' Bericht iiber 

 die Theorie der physiologischen 

 Warmeerscheinungen,' 1845, re- 

 printed in ' Wissenschaf tliche Ab- 

 handluugen,' vol. i. Xo. 1, also 

 on Joule's early experiments in 

 ' Ueber die Erhaltung der Kraft,' 

 ibid., vol. i. p. 33. 



