Phil. Soc. Proc. Vol. xx. Pt. iv. 



Plate III. 



Hydrogen and 

 Mercury 



Hydrogen 

 Low pressure 



Fis. 2. 



On : non-oscillatory 



Off: oscillatory 



Hydrogen 

 High pressure 



Nitrogen 



Ofif 



Xon-oscillatory 

 discharge 



Nitrogen 



Fig. 4. 



