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



Plate II 



O H, 



(1) Air, Oxygen, Hydrogen 

 and trace of Helium 



(2) Oxygen, Hydrogen and 

 trace of Helium 



(3) Excess of Helium and 

 trace of Air and Oxy- 

 gen 



On 



OfE 



(4) Oxygen, Hydrogen and 

 Helium and trace of 

 Air 



On 



Off 



Fig. 3. Photographs showing the effect in mixtures of gases studied. 



