476 Mr Baker , Influence of Ultra Violet Radiation , etc. 
(b) Ultra violet light falling on the kathode, 
250 cells start the discharge ; 
249 cells do not start discharge. 
Very little importance is attached to the difference in the 
potentials required to start the discharge in the two directions 
in the dark, as the copper rod was in a narrow tube, while the 
zinc had plenty of space about it. 
To Professor J. J. Thomson are due my best thanks for 
suggesting the investigation and for his ever ready advice and 
encouragement. 
