V 
7i 
170 DR. T. R. MERTON AND PROF. J. W. NICHOLSON ON 
Table XIX. — -General Emission of Helium Series. 
Helium and 
Series. 
A. 
Pure Helium. 
Low pressure. 
trace of 
hydrogen. 
He + Hi. 1 
1 
Difi'use. 
5876 
10 
10 
10 
10 
Sharp . 
4713 
2'24 
5-24 
2-45 
6-77 
Principal .... 
3888 
13-4 
6-41 
11-42 
16-45 
It is perhaps desirable to remark again at this point that the numbers in any one 
column give no indication of the relative emissions of energy in these wave-lengths, 
the properties of the plate being widely different in the three regions of the spectrum 
concerned. Comparison is justifiable in rows, but not in columns. 
Low pressure produces a considerable enhancement of the Sharp series relatively 
to the Diffuse series—in fact the intensity is doubled—and a simultaneous reduction 
of the Principal series of an equivalent magnitude. 
A trace of Hydrogen produces only small differences in the relative emission of the 
three series, as determined by these lines. The Sharp series is slightly enhanced, and 
the Principal series to a somewhat greater degree in relation to the Diffuse series. 
This enhancement of the Principal series continues, but not in a very important 
manner, with the addition of more Hydrogen, whose effect, however, is very striking 
in the case of the Sharp series, which is increased threefold in intensity, as compared 
with the Diffuse. 
The corresponding table (Table XX.) for Parhelium is as follows:— 
Table XX. — General Emission in Parhelium Series. 
1 
j Series. 
1 
A. 
Pure Helium. 
• 
Low pressure 
Helium with 
trace of 
H2. 
r 
He-f H 2 . 
! 
1 Diffuse. 
6678 
10 
10 
10 
10 
i Sharp . 
5047 
1-73 
absent 
1-49 
3-98 
Principal .... 
5015 
19-8 
45-9 
12-0 
20-6 
The enhancement of the Sharp series found in the case of Helium, under low 
pressure, may occur here also even to a somewhat greater extent, without appearing 
on the plate, and the efiect cannot be tested. But the most significant feature is 
undoubtedly the behaviour of the Principal series characterised by A5015, which is 
greatly enhanced in relation to the Diffuse series, in complete contrast to the 
corresponding effect in Helium. 
0 
