MECHANICS AND RADIUM. 211 



parent, and they are refractive because the luminous 

 vibrations are communicated to the movable electrons 

 which are susceptible of oscillation, and a refraction 

 of the original beam of light results. 



I cannot here give the details of the calculations. 

 I will content myself with saying that this theory 

 accounts for all the known facts, and has enabled us 

 to foresee new ones, such as Zeeman's phenomenon. 



V. 



MECHANICAL CONSEQUENCES. 



Now we can form two hypotheses in explanation of 

 the above facts. 



1. The positive electrons possess an actual mass, 

 much greater than their fictitious electro-magnetic 

 mass, and the negative electrons alone are devoid of 

 actual mass. We may even suppose that, besides the 

 electrons of both signs, there are neutral atoms which 

 have no other mass than their actual mass. In this 

 case Mechanics is not affected, we have no need to 

 touch its laws, actual mass is constant, only the move- 

 ments are disturbed by the effects of self-induction, as 

 has always been known. These perturbations are, 

 moreover, almost negligible, except in the case of the 

 negative electrons which, having no actual mass, are 

 not true matter. 



2. But there is another point of view. We may sup- 

 pose that the neutral atom docs not exist, and that the 

 positive electrons are devoid of actual mass just as 

 much as the negative electrons. But if this be so, 

 actual mass disappears, and either the word mass will 



