INTENSITY RELATIONS IN THE SPECTRUM OF HELIUM. 
161 
Table XIII.—Intensities of Helinm Lines under Varioiis Conditions. 
X. 
Photograph (a). 
Photograph {h). 
Photograph (r). 
Photograph {d). 
1. 
1. 
1. 
1. 
7065 
absent 
5-69 
5-16 
6-38 
6678 
3-41 
64-7 
63-2 
49-0 
5876 
12-30 
437 
288 
200 
5047 
absent 
11-2 
9-44 
19-55 
5015 
15-6 
128 
75-7 
101 
4922 
4-32 
42-1 
33-3 
47-3 
4713 
6-44 
97-9 
70-6 
135-5 
4471 
39-18 
571 - 5 
322 
390 
4437 
absent 
8-81 
6-79 
11-8 
4388 
4-07 
29-3 
22-4 
28-4 
4169 
absent 
] -60 
absent 
2-19 
4144 
absent 
7-13 
4-41 
7-41 
4121 
absent 
23-4 
15-0 
25-5 
4026 
6-24 
67-5 
46-8 
73-8 
4009 
absent 
1-52 
absent 
2-02 
3965 
2-99 
26-7 
14-0 
24-2 
3888 
7-89 
585 
329 
329 
Helium Series under Various Conditions of Pressure and of Purity .—We may 
begin the discussion of the phenomena contained in the last table by a consideration 
of the Diffuse and Sharp series of Helium. The relative intensities of lines belonging 
to different series, including the classical example of A5876 and X5015 at low 
pressures, will be considered in a later section. 
We shall for the moment confine attention to the question of energy transfer up or 
down the series, from one line to another of the same series, produced by very low 
pressure—as distinguished from “ordinary” conditions of pressure—or by admixture 
of a large or small quantity of Hydrogen. In each photograph we reduce the 
intensity of A5876, in discussing the case of Helium, to 10 on any necessary scale, 
with corresponding calculations of the reduced intensities on the same scale, of X4471 
and X4026. The results are shown, with the corresponding ones obtained in the same 
manner for the Sharp series—represented by the lines XX7065, 4713, 4121 —in 
Table XIV. There are three members in each case, and we have accordingly 
appended also the intensity ratio of the two other members, as they must also be 
compared with one another as well as with the first member. In the case of the 
Sharp series it has been more convenient to take X4713 as the standard instead of 
X7065. 
In discussing these results we must, of course, take the ordinary spectrum of pure 
Helium given on photograph (6), and refer the others to this as a standard. 
Inspection of the table reveals the following main characteristics of these spectra :— 
Low pressure definitely enhances the line X4471 Avith respect to X5876, and at the 
VOL. COXX.-A. 2 A 
