138 Prof. J. Zeleny on the Ratio of the Velocities of the 



§ 9. Distribution of Electrification between two Plates. 



When conduction is taking place between two plates, 

 through air exposed to Rontgen rays, free electrification is 

 distributed between them ; and it is of importance in some 

 experiments to know the nature of this distribution, and how 

 it is affected by the difference of velocity of the ions. 



The electrification of the air is due to an excess of ions of 

 one sign, and to find directly the way in which this excess is 

 distributed the following experiments were performed : — 



Fiff. 7. 



To Elect co metee 



111 the apparatus used (fig. 7) P and Q are two parallel, 

 9 centim. square, zinc plates. These are enclosed in a metal- 

 lined box RS, and by means of insulated wires are connected 

 to the opposite poles of a battery N, whose middle point is to 

 earth. C and I) are two slits, having a flat opening 2 centim. 

 by 3 millim., and being made of an imperfect insulating 

 material with a conductivity a little larger than that of the 

 conducting air. 



They extend well into the space between the plates, and 

 are fastened to two slides, A and B, which allow the box with 

 its plates to move up and down between them by air-tight 

 joints. By means of F air can be blown through the slit G 

 into D, and out through the insulated plug of glass-wool E, 

 which is connected to a pair of quadrants of an electrometer. 

 After the air-blast has been going a little time a definite 



