Electric Discharge in Gases. 



51 



I. 



II. 



III. 



E. 



W. 



E. | W. 



E. 



170 

 40 

 20 

 10 



W. 



60 

 125 



40 



4S 



170 

 135 



85 

 55 

 32 

 20 

 11 

 5 



68 

 72 

 93 

 78 

 73 

 45 

 45 

 54 



160 



130 

 82 

 60 

 30 

 14 



100 

 112 

 110 

 100 

 62 

 20 



When the mica shield touched the electrode, a very great 

 rise was observed. 



The course of production of heat, as given by measurements 

 with the thermometer, is thus exactly the same as that fur- 

 nished by measurements with the thermo-electric element. 

 From a minimum in the positive discharge it rises to a maxi- 

 mum, then sinks to a minimum, finally attaining a second 

 maximum at the kathode itself. 



The causes of these peculiarities in heating-effect cannot be 

 determined without further experiment, but in the meantime 

 we may note the following points. 



The following equation holds good for any body traversed 

 by the current 



d 2 v yv a 2 v 



where Y denotes the potential at any point and p the density 

 at the same point. If we have a tube (whose axis is the axis 

 of x) which the current fills uniformly, then 



jjTa = jjr = 5 consequently ^ = -4tt/>. 



In ordinary conductors p = : hence ^— is constant, or, for 



unit length, Y — Vi = constant, being proportional to the 

 resistance w. Hence if a denote an absolute constant, 



Hence, with equal resistances, there must be equal productions 

 of heat in equal lengths. If we find that the heat-production 

 at different points of a tube is not constant, this is explained, 

 if p = 0, by the fact that the resistance at different points of 

 the tube is very different. 



We have seen that close to the electrode we have a very 



E2 



