MECHANICS AND RADIUM. 203 



more than a hundred times too low, but they were 

 subject to certain causes of error. The question has 

 been taken up again by Wiechert, with the help of an 

 arrangement by which he makes use of the Hertzian 

 oscillations, and this has given results in accordance 

 with the theory, at least in the matter of magnitude, 

 and it would be most interesting to take up these 

 experiments again. However it be, the theory of 

 undulations seems to be incapable of accounting for 

 this body of facts. 



The same calculations made upon the fi rays of 

 radium have yielded still higher velocities — 60,000, 

 120,000 miles a second, and even more. These 

 velocities greatly surpass any that we know. It is 

 true that light, as we have long known, travels 1 86,000 

 miles a second, but it is not a transportation of matter, 

 while, if we adopt the emission theory for the cathode 

 rays, we have material molecules actually animated 

 with the velocities in question, and we have to enquire 

 whether the ordinary laws of Mechanics are still 

 applicable to them. 



II. 



Longitudinal and Transversal Mass. 



We know that electric currents give rise to pheno- 

 mena of induction, in particular to self-induction. 

 When a current increases it develops an electro-motive 

 force of self-induction which tends to oppose the 

 current. On the contrary, when the current decreases, 

 the electro-motive force of self-induction tends to 

 maintain the current. Self-induction then opposes 

 all variation in the intensity of a current, just as in 



