Complementary Notes. 



(1) As mentioned in the Preliminary Notice^ and as will be 

 seen in the later communications, the properties attributed in the 

 present paper to " X " rays, belong not to these rays, but to a new 

 kind of rays, to which I have given the name of " N " rays. 

 The experiments are correct, and the rectification only applies 

 to the nature of the rays which have been studied. 



(2) What I attributed then to "S" rays is, in reality, due 

 to diffused " N " rays. The rotation of the plane of polarization 

 of " N " rays by active substances is perhaps very great, since 

 their wave-lengths are very small. It may be, then, that the 

 angles I have observed are merely the remainders obtained by 

 subtracting 360 once or several times from the real rotations. 

 For the same reason, the rotations in a contrary direction could 

 be apparent only. Investigation on this point remains still to 

 be carried out ; the operations should be conducted successively 

 on each of the homogeneous pencils resulting from the dis- 

 persion of a pencil of " N " rays by an aluminium prism. The 

 existence of magnetic rotatory polarization has recently been 

 shown by M. H. Bagard, whose investigations are still in 

 progress. (C. R. t. cxxxviii.) 



(3) Unpolished mica arrests a pencil of " N " rays ; these 

 are not, however, absorbed, but only diffused, as in the case 

 of light. 



(4) Rock-salt is in reality transparent. What had at first 

 misled me was that the plate of salt I used, having been sawn 

 out of a large block, had remained unpolished. In this state it 

 was only translucent, whether for " N " rays or for light. When 

 polished with wet paper, it becomes transparent both for 

 " N " rays and light ; when the polish disappears, it becomes 

 translucent again. 



