1088 Mr. D. Coster on the Spectra of X-rays 



the lines of the /3-group for Pb taken with a rocksalt crystal ; 

 fig. 2 gives nearly the whole L-spectrum of Rh * taken 

 with a gypsum crystal. For the lines <y 2 an d 7 3 the case is 

 much similar : for the heaviest elements they are approxi- 

 mately of equal intensity ; for Ta 73 seems to be prominent ; 

 for Ba and Cs 73 is ; still fairly strong, whereas y 2 can scarcely 

 be perceived. This fact may imply that the disturbances of 

 the inner atomic field which give rise to /3 4 and y 2 (the 

 azimuthal quantum number does not change for these lines) 

 are less important for the lighter elements. But the change 

 of relative intensity of /3 3 and /3 4 must partly be accounted 

 for as a change in the intensity of j3 3 . This line seems to 

 correspond to a transition less probable for the heavier 

 elements than for the lighter ones. 



In the case of rj-l and 7s-/3 6 doublets a corresponding 

 change of the intensities could not be observed. For all 

 elements I is about 2-3 times as strong as 77 and /3 6 2-3 

 times as strong as 75. The lines rj and 75 like /3 4 and y 2 

 correspond to transitions for which the azimuthal quantum 

 number does not change ; the lines I and /5 6 correspond 

 to transitions for which the azimuthal quantum number 

 decreases, whilst the lines /3 3 and 73 correspond to transitions 

 for which it increases. 



§ 7. Another interesting result of this investigation of the 

 L-spectra of the lighter elements was the discovery that the 

 two most intense lines of this spectrum, a x and ft, show a 

 complicated structure, which has not been observed for the 

 heavier elements, or is at any rate much less pronounced. 

 Both lines in question show a broadening on the short wave- 

 length side. This cannot be ascribed to any peculiarity in 

 the experimental conditions, as it has a very regular structure 

 which is independent of the time of exposure. On the other 

 hand, the line /3 3 which on several long exposed plates was 

 very intense showed no such structure, appearing merely 

 somewhat diffuse on both sides. For the o^-line this broaden- 

 ing ends fairly abruptly, so that the edge could be measured 

 with sufficient accuracy. From this the wave-length corre- 

 sponding to this edge could be calculated. (A correction 

 must be made for the half width of the slit.) In the following 

 tables this wave-length has been called u x '. This must be 



* The satellites of cc l and j3 l (see Part III. § 7) have not been well 

 reproduced on this plate. They were more easily visible on the original 

 photograph. On the reproduction Sn La stands erroneously for Fe Ka 

 2nd order. 



