7-J DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
Ijetweeii A1 and In, as is seen at once from the values lor the first two lines of the 
Si series, wliich are as follows ;— 
Al. 
Ga. 
In. 
3961 
311 
'4172 
339 
4511 
2660 
59 
2719 
313 
2932 
(The other allocation 2780 gives differences 120 and 152 for the second line, in 
closer ratio to those of the first.) 
r 3002 2043 3258 
[ 2575 2500 2714 
I’hey apparently helong to series of S and 1) type correlated to the typical ones. 
The limit is in the neighbourhood of 47600. If the real one is 47600 + the formulm 
obtained for them give the following denominators, viz. :—■ 
For S 1-206850-•0002477F-(-052878-T)002022f)m-h 
D -713106-•0005303f+(-2450IO+-0008706f)m-\ 
and f may he as large as ±250. 
In the InS Eydberg allocated the three first doublets and the first of the next. 
Kayser and IIunge lirought the observed up to six, and the second lines of the next 
two S 2 (7, 8). This is curious, as the only example so far observed in which the second 
series appears stronger than the first. I find, however, that lines observed in the 
spark spectrum by Hartley and Adeney (‘Eoy. vSoc. Trans.,’ 1884), viz., 2332-2 and 
2101 - 2 , occupy the places for Si(7) and 82 ( 0 ). The other measures are K. and R.’s. 
Their value for 2357-7 is, however, clearly 1 A.U. too small. It gives an incorrect 
value for v which the formula corrects. 
In TTS Eydberg gave the first four doublets and the five succeeding lines for TIS 2 , 
indicating a similar result to that of In, viz., that the 83 series are more persistent 
than the 81 . Kayser and Eunge extended the list Ijy adding nine lines to the 
81 series, thus completing nine doublets and adding four extra lines to 81 . It is 
possible that even here the 83 may be the more persistent, and that they have not 
been observed because they are situated much farther down in the ultra violet. The 
TIP series again are due to Paschen. The line X = 4678-3 is really a mean position 
for tlie douldet TlPi 3 ( 7 ), the components being too close for resolution. 
l^Alay 13, 1912.—Whilst the foregoing has been passing through the press more 
complete lists of spectral lines, including those in the visible region, have been 
piddished l)y Exner and TIaschek."^ It is possible, therefore, to see how far tlie 
* ‘Die Spektren der Elemeute bei iiormalen Druck,’ Fkanz Deiuicke, Leipzig u. Wien, 1911. 
