262 
PEOF. A. FOWLEE ON SEEIES LINES IN SPAEK SPECTEA. 
without identification, but a preliminary examination of these has given no certain 
evidence of series for which the series constant would be 9N. 
The Wolf-Bayet (“bright-line”) stars are of special interest in this connection, as 
they are generally considered to represent the first stage in the condensation of 
nebulous matter into stars, and in many of them the proto-helium lines are a 
prominent feature. Nicholson has suggested that some of the lines may belong to 
series which can be represented, in wave-lengths, by the formula 
X = 3646 
(m±j ) 2 
{'m+ 3 ) 2 —4 
where 3646 is the limit of the hydrogen series.* The lines were regarded as a 
possible extension of the hydrogen spectrum, hut on the supposition that other lines 
associated with them may coincide with the Balmer series, Dr. Bohr has pointed out 
that all the lines might be united in a single series and might be attributed to 
lithium. The binding of an electron by a lithium atom from which the three electrons 
have been removed would, on the theory, give rise to such a series, namely, 
or 
X = 3646 
rn 2 
m 2 — 36 
5 
n = 27418- 
9x109675 
This hypothetical series would thus be of the “ 9N ” type, but its existence in this 
form is not confirmed by the observational data. Omitting the lines which would 
coincide with the ordinary lines of hydrogen, the earlier members of the series would 
be 5697, 5193, 4633, 4466, 4243, &c. Of these only the first, third, and fourth are 
possibly represented in the Wolf-Bayet stars, and since the intensities should degrade 
in regular order in passing from red to violet, the absence of a line at 5193 is 
conclusive proof that the observed lines do not form a series of the “ 9N ” type. 
I 11 a further discussion of the spectra of the Wolf-Bayet stars, Nicholson has 
arranged most of the lines in a number of series of a different character, in which the 
Bydberg constant is replaced by various fractional parts of its value for hydrogen.! 
The numerical relations traced in this way are very striking, but the individual series 
indicated are very fragmentary, and such lines do not always occur together in the 
same star. The suggested series are also remarkable as involving different fractional 
values of the Bydberg constant for series proceeding to the same limit. 
The general progression from series of the N type to those of the 4N type in passing- 
through the stellar sequence would suggest that further change, if any, would be in 
the direction of multiples, rather than fractions, of N in the series formulae. It is 
* 1 Monthly Notices E.A.S.,’ vol. 73, p. 382 (1913). 
f ‘ Monthly Notices E.A.S.,’ vol. 74, p. 118 (1914). 
