HELMHOLTZ IN BERLIN 



kinetic energy. Consequently we must extend the 

 conception of energy from that of potential energy, 

 or the energy of position, so as to include the energy 

 of motion, which may appear as heat or other forces. 

 The loss of kinetic energy in the above case will then 

 be equal to the amount of heat produced. This idea 

 led Mayer (see p. 47) to the fundamental conception 

 of the equivalence of heat and mechanical work, and 

 it no doubt also guided Helmholtz in writing his tract, 

 Die Erhaltung der Kraft. The outcome of this dis- 

 cussion is that the work done by any conservative 

 system in changing from one configuration into 

 another, depends on the configurations at the be- 

 ginning and the end of the process, and not on the 

 intermediate stages. The tract was intended to show 

 the theoretical and practical importance of the law 

 of the constancy of energy, not from a priori con- 

 siderations, but by induction from facts, and especially 

 from vain attempts to discover or invent the per- 

 petual motion. It does not tell us anything about 

 the mode by which the configuration is changed, or, 

 to put the matter in other words, it does not define 

 the route followed by the system in passing from the 

 first configuration into the last. 



The publication of this tract, which has had so 

 great an influence on science, was often referred to 

 in later years by Helmholtz. It was therefore fitting 

 that he should crown the edifice he had reared by 

 the great papers of his later years, in which he re- 

 ft 



