Vlli PRELIMINARY NOTICE 



some confusion was bound to arise between 

 the phenomena appertaining to each. In 

 particular, the preliminary researches which 

 the author had made 1 on the velocity of 

 propagation of " X " rays apply in reality 

 not to " X " rays, but to " N " rays. He 

 had found that the velocity of propagation 

 was the same as that of Hertzian waves, 

 and consequently of light. Since the pro- 

 perties of " N " rays, taken in their entirety, 

 do not leave any doubt that these rays are 

 a variety of light, this determination of their 

 velocity is now nothing more than a verifica- 

 tion of an assured fact. Nevertheless, this 

 verification seemed not altogether superfluous ; 

 it proves at least that the experiments have 

 been carried out with care. 



1 Comptes Rendus, t. cxxv. pp. 666, 721, 763. 



