1086 Mr. D. Coster on the Spectra of X-rays 



which might be supposed to exist by analogy with the 

 transition M 2 -h\, which gives rise to the line « 2 . 



Pairs of lines the frequencies of which show a relativity 

 doublet difference occur very often in the X-ray spectrum, 

 but those which would form a screening doublet do not occur 

 at all in virtue of the a-b rule (see diagram I.). But we may 

 find lines the frequency difference of which is either the sum or 

 the difference of two screening doublets. To the former class 

 belong fit-r) and 72-75, to the latter ftg-fii and 73-71. As the 

 screening doublets are approximately proportional to the 

 effective nucleus charge of the atom, the differences of the 



Table V. 

 Differences in 



Pi-ri 



37 Eb 



38Sr 



0921 

 927 



39Y 





40 Zr 



941 



41 Nb 



946 



42 Mo 



955 



44 Eu 





45 Eh 



973 



46Pd 



979 



47 Ao- 



989 



48 Cd 



996 



49 In 



999 



50 Sn 



51 Sb 



52Te 



1004 

 1006 



55 Cs 



1027 



56 Ba 



74 W 



1045 

 1136 



83 Bi 



1200 



72-75 



Ar/3, 



73-7i 



0-666 

 676 



686 



704 

 712 

 715 

 718 

 724 

 731 

 740 

 745 

 760 

 756 

 771 

 770 

 822 

 910 



! 0242 

 237 

 232 

 226 

 223 

 218 

 210 

 209 

 204 

 203 

 200 

 198 

 196 

 194 

 196 

 192 

 192 

 202 

 224 



0-550 

 547 

 547 

 531 

 527 

 522 

 520 

 512 

 512 

 510 

 511 

 510 

 505 

 502 

 517 

 495 



square roots of the frequencies of these lines are easily seen 

 to be nearly constant for the different elements. These 

 differences are shown in Table V. This table in connexion 

 with Table IV. most strongly supports the identification of the 

 lines which has been proposed by the author. The dif- 

 ferences /3 4 -t; and 72-75 increase slowly with increasing atomic 

 number. This is due to the fact, that in every line-frequency 

 the screening constant of the initial as well as that of the 

 final level is involved, and these screening constants in 

 general will be different. For the heaviest elements the 

 relativity correction here also plays a part. 



The values which I have given for 73 may be verified 



