at the Electrodes in Vacuum-Tube Discharge. 627 



Table V. 



Drop at Cathode (volts) with Current— various Gas-pressures. 

 (Steel cathode — Area 2*5 sq. cm.) 



G-as Pressure 

 (mm.) 



1 3'6 



26 



1-7 



1-4 



10 



07 



03 



Current 

















(milliamps.). 

















0-5 









305 



300 



355 



415 



0-6 







280 











10 





285 



295 



325 



340 



405 



530 



2-0 



275 



305 



330 



365 



415 



505 



690 



30 



280 



325 



370 



405 



480 



595 



860 



40 



295 



365 



410 



445 



530 







50 









485 



565 







60 



315 



400 



460 











this group of lines may, with exception of that for a pressure 

 of 3*6 mm., be expressed by the simple mathematical 

 equation, 



V = 245 + -(i + 0-6), 



where V is the drop at the cathode, i the current, and p the 

 gas-pressure. 



For each gas-pressure, p, the value c is as follows : — 



p ... 0-3 0-7' 1-0 1-4 1-7 2-6 3*6 



.. 51 



69 



62 



63 



58 



62 



40 



From the irregularity with which c fluctuates about the 

 recurring value 62, we are led to conclude that under ideal 

 conditions it is a constant. Omitting that for p = 3'6 as 

 being exceptional, we obtain a mean value 61. The equation 



V = 245+— (i + 0'6) 

 P 



enables us then to calculate the value of the cathode drop in 

 nitrogen, for a steel disk, with a discharge surface of 2*5 

 sq. cm., placed normal to the axis of the discharge-tube. It 

 is observed to be valid for gas-pressures varying from 0*3 to 

 2'6 mm. The experimental arrangement did not allow of 

 reliable measurements being made at lower gas-pressures. 

 At lower pressures (not measurable) it was simply noted that 

 the lines continued to radiate from the same central point as 

 at the higher. 



