Cathode Rays and certain Chemical Effects. 227 



The arrangement o£ the apparatus was in its essentials 

 the same as that described by Glasson. The apparatus used 

 in the previous work (fig. 1 a) comprised it in part. The 

 discharge-tube B, the solenoid, and the ionization-chamber I 

 were the same ; the outlet from the ionization-chamber to P 

 being now closed. The casing of the solenoid and the 

 ionization-chamber were earthed as before, while the Faraday 

 cylinder was raised to a potential sufficient to saturate the 

 gas by a battery of a few storage-cells, whose other terminal 

 was connected through the galvanometer to earth. In these 

 experiments a potential of 10 volts was applied to the 

 cylinder. Experiments, as before, were made at various 

 pressures, rays of known velocity being made to cross the 

 ionization-chamber I. 



The effective length of path of the rays in the chamber 

 was the distance between the entrance o to the chamber and 

 the entrance to the Faraday cylinder F. It was the ionization 

 in this length of path that was examined. 



The current through the chamber, as measured by the 

 galvanometer during any one experiment, w r as evidently 

 made up of 



(1) the current carried by the rays themselves, 

 and (2) the ionization current. 



The direction of the former was independent of the sign 

 of the potential applied to the Faraday cylinder, while the 

 latter could be changed in direction if the imposed field was 

 reversed. By such a reversal of the potential of the Faraday 

 cylinder the sum and the difference of the effects (1) and (2) 

 were obtained. 



If, in any one instance, n is the number of cathode rays 

 crossing the chamber per second ; and a the number of pairs 

 of ions made by one corpuscle in travelling 1 cm. in nitrogen 

 at a pressure of 1 mm. of mercury ; and I is the length of 

 path of the rays in the chamber, we have as follows : 



The current carried by the rays = ne. 



The saturation current carried by the ions = odpne. 



When the Faraday cylinder is positively charged the 

 current is given by 



C\ = ne + odpne , 



and when the cylinder is negatively charged 



c 2 = ne — cdpne. 

 Thus 



C l — C 2 7 



- 1 = cilp. 



(1 i + c 2 



