350 DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



Xenon. Xenon also shows two spectra, withoTit capacity in the red region and 

 with it, extending far into the ultra-violet. Practically the only material at disposal 

 is contained in the extensive lists of BALY* (red spectrum 6198 -2536, blue 

 6097 2414) with an accuracy of about '03 A. This is supplemented by observations 

 by LIVEING and DEWAR,! especially by longer wave-lengths up to 6596, but 

 unfortunately only measured to the nearest unit. 



BALY draws attention to the large number of lines apparently common to both 

 Kr and X. The number of lines in the whole spectrum is very large. BALY gives 

 1376 in the blue spectrum, but perhaps the most noticeable point for our present 

 purpose is the great variability with change in the conditions of excitation. This is 

 very clearly indicated by a comparison of intensities of corresponding lines as observed 

 by L., D. and B. The following are a few examples out of a large number illustrating 

 this. The numbers following a wave-length give the intensities -as estimated 

 respectively by BALY and by LIVEING and DEWAR : 



5191 5, 6 4890 5, 3 



5188 4, 3 4887 5, 



5080 7, 2 4884 1, 4 



5068 not seen, 5 4883 6, 



5045 3, 6 4844 10, 10 



As between the two spectra also, a fact noticed by L. and D. is of importance. 

 They say " there is one very remarkable change in the xenon spectrum produced by 

 the introduction of a jar into the circuit. Without the jar the xenon gives two 

 bright green rays at about X4917 and X4924, but on putting a jar into the circuit 

 they are replaced by a single, still stronger, line at about 4922. In no other case 

 have we noticed a change so striking." They also state that changes occur with the 

 same kind of discharge as between different tubes. These are clear cases of oun 

 displacements. PAULSON again (loc. cit.) gives some constant separations in the first 

 spectrum. The triplet separations observed are about v l = 1778, v a = 814, in due 

 order of magnitude with those for Kr. No line suitable for S (l) comes within the 

 observed region, but there are two lines with W.N. 40375'40, 39561'50 separated by 

 813'99, which would serve for S 2 (l) and S 3 (l) and are in a similar position to the 

 KrS lines. They clearly suggest that the S! (l) line is at -42 153 "39, using 

 "i = 1777'90 as found from the S 2 set. This is further substantiated by employing 

 the value of the e link, found below to be 7314, as a sounder. It requires a line at 

 about 34839, and such a line is found at (< l) 3483678 (but see discussion under 



* ' Phil. Trans.,' A, vol. 202, p. 183 (1903). 



t ' Roy. Soc. Proc.,' vol. 68, p. 389 (1901) ; ' Coll. Papers,' p. 494. 



