PHENOMENA RELATING TO THE SPECTRA OF HYDROGEN AND HELIUM. 255 
Hydrogen evidently shows the effect in a more pronounced manner than Helium, in 
that the fourth line, H«, shows it more than the third. 
Our results are also in accordance with those of Sir J. J. Thomson* who found 
that the intensity ratio ~ was greater in the negative glow than in the positive 
H a 
column. 
The enhancement of the later members of the Balmer series in the presence of Neon 
is in accordance with the observations of Liveing and Dewar! who found that it was 
possible to observe ultra-violet members of the series in a mixture of Neon and 
Helium containing Hydrogen, although these lines could not be found in vacuum tubes 
containing pure Hydrogen. 
(IX.) The Spectrum of Neon. 
Except for certain series suggested by Rossi| involving only a few lines, the 
greater part of the Neon spectrum is of unknown structure, although some constant 
differences of frequency haye been detected by Wats ON. § 
One of the advantages of the mode of experiment described in this communication 
is that it may assist in elucidating the structure of very complicated spectra, and it 
may, in fact, be combined with investigations of the Zeeman effect, which has been 
used hitherto, as by Dufotte|| in connection with the secondary spectrum of Hydrogen, 
in the detection of different classes of lines in such spectra. A preliminary exami¬ 
nation of a portion of the Neon spectrum leads to some very interesting results which, 
however, at present cannot be brought within a general scheme of interpretation, 
owing to our lack of knowledge of series relations with which they are without doubt 
connected. The table contains a comparison of the spectra of Neon in the ordinary 
discharge and from the bulb, the gas containing a little Hydrogen. The enlarged 
length of the wedge was 42 mm. Only the stronger lines in the red and yellow have 
been subjected to examination, and if series exist in the spectrum, their leading 
members in the red and yellow should decrease considerably in intensity in the bulb, 
but on the whole, less considerably towards the yellow—provided that Neon behaves 
like Hydrogen and Helium. 
There is a preponderance of small ratios in the case of the very strong lines, and the 
larger ratios are in general for the smaller wave-lengths, while the two smallest wave¬ 
lengths examined show enhancement, which is not found elsewhere in the list. These 
facts give some support to the view that a complicated system of series may be 
present. If, on the other hand, the spectrum is more in the nature of a band, as in 
* ‘Roy. Soc. Proc.,’ vol. 58, p. 244, 1895. 
t ‘Roy. Soc. Proc.,’ vol. 67, p. 467, 1900. 
t ‘Phil. Mag.,’ XXVI., p. 981, 1913. 
§ ‘ Astrophys. Journ.,’ XXXIII., p. 399, 1911. 
|| ‘ Ann. de Chini. et Phys.’ (8) 9, p. 361, 1906. 
2 N 2 
