X-ray Spectra of the Elements. 695 



Since at that time methods of wave-length measurement 

 had not been developed, it was suggested that the quality 

 of X-rays should be defined by this formula in terms of the 

 speed (*•) of the electron carrying the same amount of 

 energy as the X-ray under definition. These speeds had 

 been measured for a number of elements between alu- 

 minium and silver, from which it had been concluded that 

 for the K series v = w x 10 8 cm./sec, and for the L series 



v={-^ — 25 JIO 8 cm./sec, where w = the atomic weight of 



the element. 



With the advent of crystal spectrometry and the accurate 

 measurement of a large number of the X-ray spectra, 

 Moseley * in two well-known papers showed that atomic 

 number was more fundamental than atomic weight and 

 proposed the relation v — A(N — b) 2 , where v is the frequency 

 of the characteristic radiation (strong 1 « line in the K series, 

 strong « line in the L series), X is the atomic number of 

 the element, and A and b are the series constants. 



It is one object of this note to point out that the relation. 

 v=.G.w-\-D becomes Moseley 's relation if we put 



w = 2Xf and hnr' 2 = hv, 



which is the usual quantum relation. 

 For then 



Vhv 



i- 2 = = (2C.X + D) 2 , 



m 



m 



v=^(2C.X + D) 2 , 

 v = aQ$ + d) 2 , 



where a=—= — and d=„ )( ,, which is Moseley's relation. 



lie verting to u = C .w-\-D, which is now revived in 

 the form r — CX-f-D, the following table shows the values 

 of v for the K series a line from tungsten to sodium, approxi- 

 mately calculated from \mi?=hv%. 



* Phil. Mag. 1913, vol. xxvi. p. 1024, and 1914, vol. xxvii. p. 712. 

 t See Bohr, Phil. Mag-. 1913, vol. xxvi. p. 499. 



t The values of \ vrere taken from Tables given bv Uliler, Phys.Eev. 

 vol. ix. No. 4 (1917). 



