DE. W. M. HICKS : A CRITICAL STUDY OF SPECTRAL SERIES. 
355 
Again the modified n = 1780 with eu( 8 i)euS 2 . These and {2e, 11)83 give 
1781-25 f 813-57 = .-i + .^2 - 1 ’ 37. 
S(12). 
[50275-68] 
-e [42961] 
- 2e-t;(2) 31219 --02 * 
-e [44739] 
-e-t;(l) 40311 -01 
[52053-58] 
[52868-88] 
- e [45554] 
2e(3) 38242 - -07 * * § 
S(13). 
[50385-80] 
[52163-70] 
-2e (2) 37534 -03 
[52979-00] 
- 2e-M(<l) 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)Si(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 therefoi’e all doubtful. 
Argon .—For the red or non-condensed spark spectrum about 360 lines between 
8015 and 2476 together with 16 lines in the ultra-red have been observed. For the 
blue or condensed spark spectrum the number amounts to about 780 between 6682 
and 2050 together with another 40 lines in the extreme ultra-violet between 1886 and 
1333. The measures in the red are due to Paschen"^ (ultra-red), Kayser,! Runge 
and Paschen,! and Eder and Valenta,§ and in the blue to Kayser,! Eder and 
Valenta,§ and Lyman|| (extreme ultra-violet). In addition we have exact inter¬ 
ferential measures in I. A. by MeissyerIF 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. ft 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). 
I ‘Astro. Journ.,’ vol. 8. 
§ ‘Denks. Wien. Akad.,’ vol. 64, p. 216 (1896). * 
II ‘Astro. Journ.,’ vol. 33, p. 107 (1911). 
H ‘ Ann. d. Phys.,’ vol. 51, p. 95 (1916). 
‘Phil. Trans.,’ A, vol. 202, p. 188 (1904). 
ft ‘ Astro. Journ.,’ vol. 6, p. 338 (1897). 
