Temperature upon Photo-electric Effects in High Vacuum. 193 



separating this discharge due to the light from the natural 

 leak o£ the system was as follows : — The natural leak was 

 observed daring the period of 30 seconds immediately pre- 

 ceding the time at which the light was turned on, then the 

 electrode was exposed to the ultra-violet light for a period of 

 exactly 15 seconds : after a lapse of 45 seconds more, the 

 deflexion was again observed ; finally, the natural leak was 

 observed during the next 30-second period. The sum of the 

 leaks during the first and last 30-second periods was sub- 

 tracted from the change in deflexion during: the intermediate 

 60-second period in order to obtain the discharge due to the 

 light. 



In order that the charged body might be perfectly screened 

 from electrical effects during these observations, the inner 

 wall of the tube was entirely covered with wire netting of 

 ^ mm. mesh, and this netting was connected to the washer w 

 and the tinfoil envelope g, and the whole system then con- 

 nected to earth in the manner shown in fig. 1. 



In order to eliminate any possible effects which gases 

 adhering to or occluded in the surface of the electrode might 

 have on the results, the tube was kept at a temperature of 

 about 400° C. during the whole process of evacuation, and in 

 addition the electrode was made the cathode of an induction- 

 coil discharge which was maintained continuously for a period 

 of several hours. 



A typical series of observations obtained with this electrode 

 is given in Table I. 



Table I. 



Temp. 



Discharge in 

 Scale Diys. 



Temp. 



Discharge in 

 Scale Dirs. 



50° 0. 



16-3 



286° C. 



13-8 



50 „ 



17-4 



290 „ 



15-1 



100 „ 



160 



292 „ 



15-4 



142 „ 



142 



295 „ 



15-2 



169 „ 



170 



296 „ 



16-2 



191 „ 



16-5 



297 „ 



15-7 



205 „ 



16-6 



298 „ 



15-9 



215 „ 



16-3 



300 „ 



15-7 



220 „ 



172 



301 „ 



16-3 



233 „ 



12-9 



301 „ 



153 



246 „ 



14-2 



303 „ 



15-7 



254 „ 



13-6 



304 „ 



155 



260 ., 



14-0 



310 „ 



15-8 



264 „ 



139 



343 „ 



15-4 



269 ., 



13-3 



343 „ 



17-0 



272 



143 



256 „ 



16-9 



275 I 



14-2 



105 „ 



17-5 



280 „ 



14-0 



53 „ 



17-0 



Phil, Mag. S. 6. Vol. 14. No. 79. July 1907. 







