DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
73 
extrapolation in the text for the sharp series of Europium is justified. The suggested 
values for the lines were 5379T and 4711'69, with a probability that they should be 
about 2 A.U. higher, if the ratio (a +A 2 )/(/>i +A 2 ) were to have the normal value 
’2152. In E. and H.’s lists are found two doublets, 5381’46, 471377 (I'l = 2631'39) 
and 5377‘13, 4709'95 {v^ = 2633’63). The former is the more probable as it gives the 
typical ratio a//x more closely. The formulae constants calculated from this are 
40363-19-N/{m + l-292265--OtSSeiw-'l^, 
giving (a +A 2 )/(ju +Ag) = ’21636 in place of the former value '21246, and, therefore, 
closer to the value as given by other elements. The alteration in the constants is so 
slight that other measures, as, for instance, the estimated density of Eu, are not 
afiPected. 
The supposed satellite series to EuS is not confirmed. At least there is no 
observed line with a wave-number near 18516-60. In the long series given at the 
bottom of p. 61, the first lines for Sj and S 2 were extrapolated to wave-numbers 
18858, &c. The nearest triplet to this is 5291'48, 4644-44, 4438’12, with wave- 
numbers equal to 18893’12, 21525’20, 22525’87, giving = 2632’08, I'g = 1000’67. 
It fits in well as the first line of the series there indicated.] 
1P JUL1912 
VOL. CCXII.-A. 
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