at the Electrodes in Vacuum- Tube Discharge. 625 



The immediate drop at the cathode, according to the views 

 expressed above, should be a function of the velocity o£ impact 

 of the positive ions, and this velocity of impact dependent 

 upon the gradient in the adjacent gas. Observations made 

 on the " immediate " and the " Warburg drop " at the cathode 

 under the same conditions, should throw some light on the 

 relation between this gradient and the drop of potential thus 

 caused at the cathode. Such observations with a circular 

 steel disk as cathode, under various currents and gas-pressures, 

 are given in Table IV. The " immediate drop " was obtained 

 with the exploring wire as close to the cathode as possible. 

 Afterwards, the " Warburg drop " was taken by shifting the 

 exploring wire into the negative glow. At the close of the 

 observations for each gas-pressure, the exploring wire was 

 returned to its positions for the " immediate drop " (as indi- 

 cated by the value of the drop), so that comparable results at 

 the different gas-pressures were obtained. As shown in the 

 table, they are, at a pressure below one millimetre, identical 



Table IV. 



Comparative Values of " Warburg " Drop and " Immediate " 

 Drop of Potential at the Cathode at various Gas- 

 pressures. 





^-0'7 mm. 



p=l'l mm. 



^=1*4 mm. 



p±=2- 



L 



j mm. 



Current 

 (Milli- 



amps.). 



\\ ar- 

 burg 

 Drop. 



Imme- 

 diate 

 Drop. 



445 



War- 

 burg 

 Drop. 



Imme- 

 diate 

 Drop. 



War- 

 burg 

 Drop. 



Imme- 

 diate 

 Drop. 



War- 

 burg 

 Drop. 



Imme- 

 diate 

 Drop. 



10 



445 



340 



320 



330 



330 



280 



205 



15 



510 



510 



3S0 



300 









... 



20 



570 



565 



410 



390 



... 



395 



300 



250 



30 



... 





450 



445 





400 



325 



275 



40 



... 









510 



505 



365 



315 



60 













565 



400 



375 



9-0 



1 

 i 













425 



425 



in value for all currents ; the gradient in the cathode dark 

 space is, therefore, practically zero. At higher gas-pressures 

 they differ for small currents, but approach equality as the 

 current increases. Both the " Warburg- " and the " immediate 



