go LIFE AND DEATH. 



7. THE PRINCIPLE OF THE CONSERVATION 

 OF ENERGY. 



In all that precedes, the principle of conservation has 

 intervened at every step. In fact, the very idea of 

 energy is connected with the existence of this principle. 

 We first discover the idea in the work of the philo- 

 sophical mathematicians who established the founda- 

 tions of mechanics: Newton, Leibniz, d'Alembert, 

 and Helmholtz ; or of inductive physicists such as 

 Lord Kelvin. Its experimental proof, sketched by 

 Marc Seguin and R. Mayer, is due to Colding and 

 Joule. 



It is Independent of the Kinetic Theory. Mayer's 

 law states that energy is indestructible; that all 

 phenomenality is nothing but a transformation of 

 energy from one form to another, and that this 

 transformation takes place either at equal values, 

 or rather, at a certain rate of equivalence. This is 

 what takes place when thermal energy is transformed 

 into mechanical energy (equivalent 425). This rate 

 of equivalence is fixed by the researches of physicists 

 for each category of energy. 



It will be noticed that this law and this theory of 

 energy, which is always presented by authors of 

 elementary books as a consequence of the kinetic 

 theory, is quite independent of it. In the preceding 

 lines we have not even mentioned its name. We 

 have not assumed that all phenomena are movements 

 or transformations of movements, whether sensible or 

 vibratory; we have not affirmed that what was 

 passing from one phenomenal determination to 

 another was the vis viva of the motion, as is the case 



