448 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
The Dj satellite gives 
928Ao = 980956+^ 3 —35‘44^, obs. error = ’ 02^93 
A., = 1057-064 +-04^3-0382^. 
Also the f{l) gives 
Aa = 1057-047+ -0190^1--0346^. 
The value of ^ in f{l) is not precisely the same as in the others as it involves the 
observed error in D„. If ^ is the value for (l) that for f{l) is ^—'l2p.j{dX = 'Q2p.^ 
and 
Aa = 1057-047+ -0190pi + -004jt>2--0346^. 
Thus _pi is of the order -9 and the best value is 
Aa = I057-064--0382^±-004. 
The value of ^ is probably a very small positive quantity. The O —C for (4) is 
dn = 1-25 pointing to a positive The data for the accurate determination from 
(F + F) are defective. Of directly observed lines those for 'iti = 6 appear reliable as 
the separations are good. This gives the limit as 27832-12 or -17. Failing any 
better determination we put '17 + ^ 
Aa 
Probably 
1057-057--0382^^±-004. 
^ > 1 and 
8 = 57-9209--0021£ ±-0002. 
d = 57-921 ±- 002 . 
The manner in which so many independent conditions fit in to give this value is 
very remarkable, and should give great weight to the accuracy of the above value. It 
must not, however, by itself be regarded as a definitive value free from all possible 
doubt without further support from independent groups of D or F series. This is not 
easy to obtain. In the first place the spectrum of A seems to approximate more to 
the doublet sets of He, and we lose the advantage of dealing with triplets. Again, it is 
clear from the way in which the lines are crowded in the region below n = 2300 and 
in which modified separations in the neighbourhood of 180 preponderate that a large 
number of displaced groups must exist, and displaced groups have generally shown a 
fragmentary quality. It is difficult, however, to deal with these in the same way as 
in Kr, X, or RaEm, because the oun is so small that the separations produced by one 
oun displacement are comparable with observation errors or uncertainties in the 
limits.^ 
* I had prepared the details of an additional D group with corresponding F and F series depending on 
a displaced D ( 00 ). As however, while supporting the above value of the oun, it does not decrease its 
possible error, no present object is to be gained by printing it. 
