1881.] 



on the Phenomena of the Electric Discharge. 



4G7 



If we examine the electric arc passing between the terminals of 

 a battery, either at ordinary atmos2)heric pressure or at other less 

 pressures, it is seen that tliere is a resemblance to tlie discharge in 

 vacuum tubes, the light emitted by different parts of it not having 

 the same intensity throughout, and that under most circumstances 

 there is a tendency to break up into distinct entities of the nature of 

 strata and ultimately to take a stratified appearance like the discharge 

 in vacuum tubes; from this we may infer that the discharge in a 

 vacuum tube is in reality a magnified arc. 



I cannot show these phenomena in a way that you could make 

 them out at the distance you are from me, but I will, with the 

 assistance of Mr. Cottrell, exhibit to you copies of photographs of the 

 arc in atmospheric air (a to n, Figs. 5 and 5a) taken in my laboratory 

 under various conditions as to distance between the terminals and 

 pressure, as set forth in the following table : — 



