﻿546 Mr. D. Coster on the Spectra of X-rays 



On one of the plates, taken with an exposure of only 

 5 minutes, H y appeared beautifully separated, the distance 

 between the components being fully three times the width 

 of either component. This makes it appear probable that 

 we can resolve also the 4th and possibly the 5th line, by 

 operating the tube with a current of comparatively small 

 intensity. 



Two series of measurements, each consisting of fourteen 

 settings on the components of H 7 , gave the following values 

 for the doublet separation : 



1st series *0568 



2nd series '0601 



Mean '0584 LA., 



which is in exact agreement with the value obtained by, 

 Gehrcke and Lau and is '004 I. A. less than the value given 

 by McLennan and Lowe. 



The actual wave-lengths of the components of the doublet, 

 H 7 are 4340*494 and 4340*435, the value given in the table 

 being, of course, the centre of the doublet. 



I have been aided in this investigation by a grant from 

 the Rumford Fund of the American Academy. 



Baltimore, U.S.A., 



June 1st, 1922. 



L. On the Spectra of X-rays and the Theory of 

 Atomic Structure. By D. Coster *. 



Part IV. t 



New Measurements in the Jj-series of the Elements 

 La (57)-Lu (71). 



1. TN Part II. of this paper I gave the results of my 



JL measurements of the elements Rb-Ba, in this part 



I will deal with those of the rare-earth metals. As is known, 



the latter elements are very similar in chemical properties, 



* Communicated by Prof. Sir E. Kutherford, F.R.S. 



t See Phil. Mag. xliii. p. 1070 (1922), Parts I., II., and TIL 



