62 LIFE AND DEATH. 



perfect form. It dominates physics under the name 

 of the theory of kinetic energy. The minds of men in 

 our own time are so strongly impregnated with this 

 idea that most scientists of ordinary culture get no 

 glimpse of the world of phenomena but by means of 

 this conception. And yet it is only an hypothesis. 

 But it is so simple, so intuitive, and appears to be so 

 thoroughly verified by experiment, that we have 

 ceased to recognize its arbitrary and unnecessarily 

 contingent character. Many physicists from this 

 standpoint consider the kinetic theory as an im- 

 perishable monument. 



However, as in the case of H. Poincare, the most 

 eminent physicists and mathematicians are not the 

 dupes of this system; and without failing to recognize 

 the immense services which it has rendered to science, 

 they are perfectly well aware that it is only a system, 

 and that there may be other systems. Certain among 

 them, such as Ostwald, Mach, and Duhem, believe 

 that the monument is showing signs of decay, and at 

 present the theory is opposed by another theory 

 namely, the theory of energy. 



The theory of energy is usually considered and pre- 

 sented as a consequence of the kinetic theory; but it 

 is perfectly independent of it, and it is, in fact, without 

 relying on the kinetic theory, without assuming the 

 unity of physical forces, which are combined in mole- 

 cular mechanics, that we shall expound the general 

 system. 



This is not the point at issue for the moment. It is 

 not a question of deciding the reality or the merit of 

 this or that mechanical explanation ; it is a question 

 of something more general, because upon it depends 

 the idea of matter. It is a question of knowing if 



