260 
DR. T. R. MERTON AND PROF. J. W. NICHOLSON ON 
problems in connection with the Balmer series, and only the final results are therefore 
exhibited. They are as follows, in the case of the ordinary discharge 
Hydrogen, Ordinary Discharge. 
A. 
Photographic 
intensity. 
Photographic 
intensity of arc. 
Absolute intensity 
of arc. 
Absolute intensity 
of hydrogen lines. 
H a 
22-08 
141-7 
26-51 
4-13 
ID 
25-06 
131-8 
5-68 
1-08 
H 
17-18 
54-25 
. 2-39 
0-757 
H, 
2-34 
8-00 
1-55 
0-453 
The fall of absolute intensity down the series proceeds fairly regularly. The 
measurements of the photographs of the Hydrogen spectrum taken in the presence of 
Neon give an estimate of the extent to which a large admixture of Neon affects the 
intensities of the lines. The particulars are contained in the following table :— 
Hydrogen mixed with Neon. 
A. 
Intensity in hydrogen 
(ordinary discharge). 
Intensity in hydrogen 
and neon (ordinary 
discharge). 
Intensity in hydrogen 
and neon (bulb). 
H a 
4-13 
6-51 
5-31 
ID 
1-08 
2-20 
2-40 
ID 
0-767 
2-26 
3-30 
H, 
0-453 
1-48 
2-63 
The enhancement of the later members of the series by Neon is very extraordinary, 
and is even more striking in the bulb than in the capillary. 
(XII.) The Nature of the Balmer Series. 
The investigation of the effect of Neon on the Hydrogen lines when produced in its 
presence, for which some quantitative data are given in the last section, cannot be 
interpreted in a satisfactory manner without a precise knowledge of the nature of the 
Balmer series. For in the case of Helium, the series arrangement into Principal and 
Subordinate series is known precisely, and -considerable differences have been found 
in the behaviour of the three types ; more especially the Principal series behaves in 
a quite different manner from the other two. Until the type to which the Balmer 
series belongs is known, moreover, no discussion of the relative behaviour of 
