in the Discharge at Low Pressures. 



187 



cathode narrows into a pencil of cathode rays, and the green 

 phosphorescence becomes much brighter and fills the tube 

 from anode to cathode. Curve C represents the measure- 

 ments under these conditions. Not much reliance must be 

 placed upon the actual magnitudes of the forces, but it can 



Fig. 4. 



lT ~j'~r~r ~~?~^TT^ 



m 



1 HI 



2CC| 





. ... 



12 (0 6 4- £ 



Distance from cathode in cm. 



be seen from the curves that at any one point in the tube 

 near the cathode the force increases rapidly as the pressure 

 is decreased. Examining the points where the curves cut 

 the axis, it is to be noticed that the dark space for curve B, 

 represented by pr, is much longer than for A, pq } while for 

 the further decrease in pressure the extension to S is 

 slight. 



Similar results were found for a tube of* diameter 4" 7 cm. 

 using a nickel cathode, except that the total length of the 

 dark space was about 8 cm., when the total length tended to 

 become independent of pressure. AVith this tube also the 

 effect of pushing the anode into the normal dark space, i. e. 



