1898.] 



Electrification by Ultra-violet Light. 



413 



for errors of experiments it seems to be true that the velocity of 

 the carrier is independent of the metal on which the light falls. 



This seems to show that the carrier is produced from the gas 

 near the plate and not from the metal itself. 



Effect of electromotive force. 



The velocity of the carrier, i.e. the velocity for a potential 

 gradient of one volt per cm. is independent of the potential of the 

 surface from which the carrier sets out. 



Experiments were also made to determine the value of the 

 velocity for different values of the e.m.f. To test this the ultra- 

 violet light from an arc was allowed to shine through a wire- 

 gauze on to a metal plate which was much larger than in the 

 experiments in the bell-jar. By using a suitable transformer, 

 potential differences, which were measured by a Thomson's Multi- 

 cellular Voltmeter, of 36"> and 700 volts beside the usual 95 volts 

 were obtained. 



When the corrections for induction are made, the radius of 

 the velocities obtained for unit potential gradient are 



We see from the above table the velocities are very approxi- 

 mately proportional to the electromotive intensity between the 



34 



VOL. IX. PT. VIII. 



