4 L. G. Raub 



the positive ions the cathode hberates a small electron current — of 

 the order of lO"^ amp. per cm.^. Driven by the intense electric 

 field these electrons double in number at every ionizing collision, 

 producing at the same time an equal number of positive ions. The 

 negative current, then — since we may safely assume no recombina- 

 tion of ions — at any point in the gas is determined by the number 

 of electrons produced per second from the cathode up to that given 

 point in the gas. Likewise, the positive current at any point is 

 determined by the number of positive ions per second entering 

 from the negative glow, plus the number of positive ions produced 

 per second by the collisions of the electrons between the point con- 

 sidered and the negative glow. Conditions in the negative 'glow 

 allow a relative evaluation of these two currents. The potential 

 gradient in the negative glow being very small, the density of 

 charge is practically zero, which means that the volume charge of 

 electricity of both signs have equal density. Since the potential 

 gradient is very small, the mobilities of the positive and negative 

 ions may be assumed equal. Equal densities of charge and equal 

 mobilities give equal positive and negative currents. 



7a /-^/ <^<^/'/-e>it' 



Fig. I 



Figure I illustrates what we may conceive to occur in an ideal 

 case where the ionizing intervals are equal and the negative glow 



