456 Dr. B. Hodgson on the Temperature of the 



There appears also to be some pressure at which the heating 

 effect for constant current is a minimum. This is shown in 



~00Z \ S-urv-e _7l UxijCjCTv 

 amps 



" 057 inn + 

 " 0-20 *m 



- -ooi- 



tot. 1-0 -mm. © 

 /'^ mm. ° 

 0-3 m-rn. -f 



Curve IV., where the temperature-pressure curve is given 

 for a current of 0'002 amp. Sufficient points were not 

 obtained, but further experiments are being carried out to 

 fix it definitely for different gases. It was thought that the 

 effect might be spurious owing to different rates of cooling 

 of the cathode for different pressures ; but no change in the 

 cooling rate was detected bv experiment. It is possible that 



