DK. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 

 Again the modified i>i = 1780 with eu^euS^. These and (2e, w)S 3 give 



1781-25 -I-813-57 = r, + ., - 1 37. 



355 



[50275-68] 



-e [42961] 

 2e-r(2) 31219 --02 



[50385-80] 



8(12). 



[52053-58] 



-e [44739] 

 e -v(l) 40311 



[52163-70] 

 2e (2) 37534 



-01 



-03 



[52868 -88] 



-e [45554] 

 -2e(3) 38242 --07 * 



[52979 -00] 

 - 1e - u <1 34216 



-04 



These higher orders are necessarily close to high orders of the D series, and many are therefore 

 apparently common to both. E.g., 34216 has been adduced as (2e)S!(7) and is also connected with a D 

 line. Also their wave-numbers are now so high that it requires two sounders in series to just reach the 

 limits of the observed region. The later identifications are therefore all doubtful. 



Argon. For the red or non-condensed spark spectrum about 360 lines between 

 8015 and 2476 together with 1G lines in the ultra-red have been observed. For the 

 blue or condensed spark spectrum the number amounts to about 780 between 6G82 

 and 2050 together with another 40 lines in the extreme ultra-violet between 1886 and 

 1333. The measures in the red are due to PASOHEN* (ultra-red), KAYSER,! RUNGE 

 and PASCHEN,! and EDER and VALENTA, and in the blue to KAYSER,t EDER and 

 VALENTA, and LYMAN|| (extreme ultra-violet). In addition we have exact inter- 

 ferential measures in I. A. by MEISSNER!! for some red lines and measures by BALY*^ 

 for a few extra lines in the blue spectrum. The red spectrum is noted for the 

 existence of the sets of constant separations discovered by RYDBERG. tt The present 

 communication, however, deals chiefly with the blue spectrum. 



The search for the S series in A is more difficult than in the cases of Kr and X. 

 There are an extremely large number of separations of about the same value but 

 clearly distinct. They range round 179 to 188, and, as will be seen later, displace- 

 ments are very common. The clue is given from the analogous S(l) lines for Kr 

 and X. The only strong triplet lines in the corresponding positions are those given 

 in the following list : 



* ' Ann. d. Phys.,' vol. 27, p. 537 (1908). 



t 'Berl. Ber.' (1896), p. 551 ; 'Astro. Journ.,' vol. 4, p. 1 (1896). 



\ 'Astro. Journ.,' vol. 8. 



'Denks. Wien. Akad.,' vol. 64, p. 216 (1896). 



|| 'Astro. Journ.,' vol. 33, p. 107 (1911). 



f ' Ann. d. Phys.,' vol. 51, p. 95 (1916). 

 ** 'Phil. Trans.,' A, vol. 202, p. 188 (1904). 

 tt ' Astro. Journ.,' vol. 6, p. 338 (1897). 



