210 Mr. M. Ishino on Velocity of Secondary Cathode Rays 



of soft Rontgen rays. It might be expected that the hits- 

 would occur oftener when the gauzes are uncharged or 

 charged positively, than when they are strongly negatively 

 charged, as v. Baeyer * and Compton f suggested. As the 

 intensity of the electric field at a point just outside a wire is- 

 47ra-, where a denotes the surface density of the electricity 

 on the wire, it is clear that, when the gauze is negatively 

 charged, a negative corpuscle will be deviated from its path, 

 so as to tend to pass around a wire, when it comes near it. 

 Keeping constant potential differences between the gauzes,, 

 while the values of the potentials were changed, the follow- 

 ing measurements of the current to the electrometer w r ere 

 made : — 



v r 



V 2 . 



v.- 



Deflexion. 



Ovolt. 



+ 6 volts. 



- 110 volts. 



2*75 cm./15 sec 



-2 



+4 



-112 



33 



-4 



+ 2 



-114 



3-6 



-6 







-116 



375 



-8 



-2 



-118 



3-85 



-10 



-4 



-120 



3-9 



-16 



-10 



-126 



4-0 



These results confirm the above idea, and show that it is 

 necessary to charge the gauzes negatively, in order to prevent 

 the corpuscles striking them. 



§ 6. Arrangement of the Potential Differences 

 between the Gauzes. 



From what precedes it is clear that we must have two 

 electric fields : 



(1) One variable electric field to measure the distri- 



bution of velocities of secondary cathode rays ; and 



(2) One electric field to stop completely ail the positive 

 ions. 



The condition necessary to prevent hits of the secondary 

 corpuscles on the gauzes is that the gauzes must be nega- 

 tively charged. 



Various arrangements of the fields between the gauzes 

 were tried, and finally the following w r as selected : 



V l= - 12 volts, V 2 = -% volts, V 3 = -12- v volts, 



where v was varied from to 2000 volts. The first potential 



* v. Baeyer, he. cit. 



t Compton/ Phil. Mag. xxiii. p. 579 (1912). 



