610 Dr. H. A. Wilson on the Current-Density at 



1*42 mm. in diameter as cathode, p is the pressure in mms. 



of mercury, I the length of the glow in cms., and the 



current in milliamperes. 

 n 



The quantity j is approximately independent of the 

 tp 



current at any one pressure, which shows that the current per 

 unit-length of cathode covered by the glow is a constant. 



c 



j- is also nearly independent of the pressure, so that the 



current per unit-length of the cathode is proportional to the 

 pressure, 



Tables IT. III. and IV. contain the results obtained with 



C 

 other wires as cathodes. In every case y is approximately 



independent of I and p. 



Table II. — Platinum wire, 0*19 mm. in diameter. 















p. 



1. 



C. 



C 



Tp- 



2-93 



5) 

 }> 



4-4 



12-8 



134 



3-4 



107 



3-66 

 3-76 

 0-875 



083 

 0098 

 0-096 



0-088 



2-18 



7-5 

 4-4 



1-56 

 067 



0095 

 0-070 



1-475 



12-5 

 11-25 



1-62 

 1-21 



0-088 

 0-073 



1-36 



86 



4-8 



4-2 



12-4 



0-794 

 0513 

 0-47 

 1-39 



0-068 

 0079 

 0082 

 0082 



093 



5> 



7-27 



5-4 



8-95 



0622 

 0-454 

 0-75 



0092 

 0-090 

 0-090 



065 



10-1 

 69 



745 

 0-496 



0-110 

 0-110 







Mean 



0'08* 



If — is divided by ird (d being the diameter of the wire) 

 we get the current-density at the surface of the cathode. 



