62 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
With 1885G for the first line the first three give 
n = 40397•87-N/{77^ + l•267384-•010971m-l}^ 
and the dift’erences of X from the observed for «i = 4, 5, 6 , / , 8 aie lespecthely — 01, 
— ’ 02 , -'34, +‘ 20 , —' 54 . The last possibly does not belong to the series. 
The agreement is good and the extrapolation is made on an observed pair So and 
S 3 , so that there is a temptation to take it as the real S series. The ^ and the a are 
not, however, analogous to those of Cd and Hg, and the ratio (a + W)/(/x + W) is 
about ’1 instead of ‘215. 
Tlie following lines also give a parallel series : • 
Si. I'l. S2. S3. 
(19913-0) 2633-80 22546-80 (1 + ) 1004-39 23551-19 (2) 
30171-45 (2) 
31626-68 (5) 2635-05 39061-73 (l). 
The first is extrapolated as before by i^i only. The second has no observed lines for 
I'l or I'.,, the magnitudes seem in wrong order, and no other orders have been observed. 
Little weight can therefore be given to it. But the formula is 
40440-60-N {(m+l-379503--0680507/r'}", 
with a limit about half way between those of Cd and Hg, and with a ratio 
(a + W)/(/x + W) = -21703. Moreover, the r/s associated with the three series show 
an increase with the limit, as should occur. For instance, Aj = -051160 would give 
respectively 2629, 2631, 2635 for limits 40364, 40397, 40440. This is quite in 
accordance with tiie general constitution of spectra."'^ The abnormal intensities may 
be due to the kind of instability referred to above. 
The D series has been filled up by using spark lines where arc were wanting. If, 
as we suppose, Eu is analogous to Hg, the spectrum taken from the salt on the 
carbon arc might be expected to partake somewhat of the nature of a spark spectrum. 
To get a spectrum analogous to the simple spectrum of Hg use should be made either 
of the arc in vacuo, or with the salt in a vacuum tube. In addition, it is reasonable 
to expect that the wanting elements throughout the horizontal row in the Periodic 
Table might show a greater amount of instability in the molecular groupings than 
the coriesponding elements in the vertical groups. I hope to show in a future 
communication that there is direct evidence of such re-groupings in other spectra, 
and that we can oljtain indications of their nature. If the grouping peculiar to a 
particular series is sulqect to an excessive disrupting force in the production of the 
spectrum, a few ordy will survive, and consequently the line observed will be faint, 
“ On the Dependence of the Spectrum of an Element on its Atomic Weight,” ‘ Brit. Assoc. Reports,’ 
1911 [p. .342]. 
