Chemistry and Physics. 335 



cathode. For copper, iron, and nickel, the percentage of JS^- 

 radiation lies between 80 and 90. In the case of platinum the 

 proportion of X-radiation is from 40 to 60 per cent. Evidence 

 for the existence of characteristic radiations softer than the K 

 and L series was obtained. — JProc. Roy. jSoc, vol. xciii (A), p. 42V, 



H. s. u. 

 9. delations between the Spectra of X-Rays. — From simple 

 energy considerations Kossel has deduced the following relations 



La = Kp - Ka 

 Ma= Ly — La, 



in which the symbols denote the frequencies or reciprocal wave- 

 lengths of the characteristic JT-rays of a given chemical element. 

 Since, however, recent experimental w^ork has shown that there 

 are two and sometimes four a lines, two or more /3 lines, and so 

 forth, doubt arises as to which data should be used in actual cal- 

 culations. In other words, the formulae are not written with 

 sufficient exactness. As the writer of this notice has met with 

 this difficulty on several occasions, it may be helpful to others to 

 have reproduced in this place the formulae given in a recent paper 

 by JuN IsHiwAKA. According to I. Maimer the first relation 

 should read 



La^ = -S^j — -^2* 



The wave-lengths given in M. Siegbahn's tables also lead to the 

 equations 



Mb = Ly^ - Z/?^ 

 M , = Ly\ - L8^. 



The author says : " I will here also remark that the following 

 relations hold very exactly through all the elements : 



Xa, - L(3, = Ll3, - Ly^ ] 



= Lp, - Ly^ ^ A\ 



(4) 



Avhere A is a constant." 



*' In order to account for these relations, especially (4), Bohr's 

 theoretical formula should be modified as follows : 





V = V 



A^ being the atomic number, n^ and 9i^ certain integers. It should 

 be supposed that JV — C^ and N' — G^ represent the numbers of 

 electric quanta contained in the " effective " nucleus charge. The 

 curve in Moseley's diagram shows further that /x^ and jn.^ are not 

 absolute constants, but vary gradually from element to element." 

 — Nature, xcix,p. 424, July 26, 1917. h. s. u. 



