INTENSITY RELATIONS IN THE SPECTRUM OF HELIUM. 
167 
wave-lengths found in Diffuse Helium is repeated in the corresponding series of 
Parhelium. For A4922 is reduced from 6’5 to 5’3. X4388 is even more reduced from 
4'5 to 3’5, and A4144 from I'l to 07. In fact each is reduced relatively to all its 
predecessors in the series. We are in this case dealing with a phenomenon of a 
different type to that caused by variation of pressure, and as suggested in connection 
with Diffuse Helium, we prefer to restrict the term “ energy-transfer ” to cases in 
which the change of intensity of a line is greater than, or less than, the change in all 
its predecessors in the series. 
The effect of a large admixture of Hydrogen is again, as in Helium, directly 
contrary to the effect of a small trace just discussed. There is an actual enhancement 
of the members of higher term number in the series. 
There remains the necessity of verifying the fact that the Sharp series of Parhelium 
presents no exceptional features, and of observing from a consideration of Hydrogen 
lines emitted in the presence of Helium in these experiments—they have been 
observed in presence of Neon in an earlier communication—the simultaneous 
effect on the lighter component of the mixture. 
For consideration of the Sharp series of Parhelium we have calculated, reducing A5047 
to intensity 10 in each case, the following intensities of the next member, A4437 :— 
A4437, intensity 7'87 in the ordinary spectrum, 7 '2 with a trace of Hydrogen, and 
6’03 with more Hydrogen. The reduction of the second member by a trace of 
Hydrogen is again evident, though not very strongly. A slight further reduction is 
manifest with more Hydrogen, but the changes are so small that we may conclude, 
from these data, that Parhelium presents no contradiction to the view that the 
reversal of energy-transfer in the Sharp series takes place at a later stage of continued 
admixture of Hydrogen than in the Diffuse series. The present numbers appear to 
indicate, as did those for the Sharp series of Helium, that the reversal is on the point 
of taking place. 
The Spectrum of Hydrogen .—In the following table (Table XVH.) the results are 
given for the spectrum of pure Hydrogen, taken in the ordinary way from a capillary 
Table XVII.—Hydrogen. 
A. 
4. 
Pure. 
Mixed with Helium. 
Ratio of 
photographic 
intensities. 
h. 
Photographic 
intensity. 
h. 
Photographic 
intensity. 
H. 
0-343 
9-9 
10-9 
17-0 
60-7 
5-6 
0-416 
7-8 
9-82 
14-6 
72-1 
9-2 
Hv 
0-490 
5-3 
6-22 
11-1 
46-9 
7-4 
H, 
0-595 
2-0 
2-31 
5-4 
9-60 
4-1 
H, 
0-705 
absent 
— 
1-3 
1-91 
