Phil. Soc. Proc. Vol. xx. Pt. i 



(a) Hydrogen and 

 Mercury 



(6) Hydrogen and 

 Helium 



(c) Hydrogen and 

 Helium, low 

 percentage 



(d) Hydrogen and 

 Helium in 

 larger per- 

 centage 



(e) Neon 



On 



Oft 



(/) Air 



Ullltl I t K II 



On 

 Off 



(gr) Air 



On 



Off 



Fig. 2. Photographs showing the enhancing effect of the field. The small lateral 

 shift is due to the camera slider, and in («) the mercury line 6152 is incUcated 

 by the dot, while in the other cases the lines that newly turn up are indicated 

 by the arrows. 



I 



