258 
DR. T. R. MERTON AND PROF. J. W. NICHOLSON ON 
These tables contain all the necessary data for the calculations of the relative central 
maxima of intensity of the Helium lines, according to the formula, 
(photo, intensity of line) (absolute intensity of arc)/(photo. intensity of arc), 
to which they are proportional. This calculation is exhibited in the next table, and 
it is convenient to take some definite line as the standard. For this purpose A3888 
has been selected. The table contains the real intensity maxima of all the important 
lines relatively to that of A388 8 , measured on an absolute scale, and produced by 
the ordinary discharge. 
(XI.) Relative Intensities of Helium Lines on an Absolute Scale.* 
Ordinary Discharge. 
A. 
Photographic 
intensity of line 
(a). 
Photographic 
intensity of arc 
(/*)• 
Absolute 
intensity of arc 
(r)- 
Absolute 
intensity of 
helium ( ocyj/3 ). 
Tabular intensity 
(Runge and 
Paschen). 
7065 
3-594 
13-7 
28-98 
7-61 
5 
6678 
32-5 
112-0 
28-00 
8-12 
6 
5876 
105-9 
116-3 
16-10 
14-7 
10 
5048 
2-839 
40-1 
7-04 
0-498 
2 
5015 
40-7 
45-3 
6-92 
6-22 
6 
4922 
21-7 
94-9 
6-08 
1-39 
4 
4714 
61-4 
186-3 
4-475 
1-47 
3 
4472 
350-2 
97-0 
3-02 
10-90 
6 
4388 
11-3 
57-3 
2-56 
0-505 
3 
4121 
4-48 
10-63 
1-61 
0-678 
3 
4026 
17-7 
5-14 
1-31 
4-51 
5 
3965 
5-23 
2-35 
1-17 
2-60 
4 
3888 
100-0 
1-00 
1-10 
100-0 
10 
The most remarkable feature of the table is the strength of A3888, the first visible 
member of the Principal series of Helium, which is much stronger than any of the lines 
of the two Subordinate series. Moreover, of the Parhelium lines, AA6678, 4922, 4388, 
(Diffuse), A5048 (Sharp) and AA5015, 3965 (Principal), the Sharp line is very weak, and 
the third member of the Principal series is stronger than that of the Diffuse—the first 
member of the Principal series is in the infra-red. It is evident, therefore, that under 
ordinary conditions, the two Principal series of Helium actually deserve their title. 
This extension to Helium of a result with which spectroscopists are familiar in some 
* In a previous section we have given a table of the photographic intensities. We have done so, at the 
risk perhaps of some repetition, because we believe that the values given for photographic intensities are 
worthy of some confidence, and in the event of more accurate data being at some future time available 
for the temperature of the carbon arc, the accuracy of our “ absolute intensities ” can at once be 
correspondingly enhanced by a simple recalculation. 
