1898.] Electrification by Ultra-violet Light. 405 



Experiment 1. 



C was connected to the negative pole of a battery of 8 volts, 

 the other pole being connected to earth. The gauze B was 

 connected to one pair of quadrants of an electrometer, the other 

 pair being connected to earth. All other parts of the apparatus 

 were earthed. When the arc light was acting the plate G lost a 

 negative charge which passed over to the gauze B and the electro- 

 meter needle showed a movement corresponding to 



60 divs. per min. 

 When a rapid current of air was directed between the plates, the 

 leak to the electrometer was completely stopped. This showed 

 that the carriers of the negative charge, which had left G, had been 

 blown out by the rapid current of air. 



If G was charged to — 24 volts the rate of leak from G cor- 

 responded to 



170 divs. per min., 

 but where the blast was in action the rate of leak was reduced to 



8 divs. per min., 

 or less than ^ of the charge which escaped from C reached the 

 gauze B ; when G was charged to higher voltages and the blast 

 kept in action, a still greater proportion of the charged particles 

 reached the gauze without being blown out. The number of 

 carriers that reached the gauze could be raised or lowered by 

 diminishing or increasing the velocity of the blast, the other 

 conditions remaining the same. 



Experiment 2. 



We have seen that a whole or part of the charged carriers 

 can be prevented from reaching the gauze B. It is now necessary 

 to show what becomes of the carriers after being blown out from 

 between the plates. The plate G was charged to — 24 volts and 

 the gauze connected to earth. The aluminium cylinder T was 

 connected to one pole of a battery of 30 volts, and the wire W 

 connected to the electrometer. There was no deflection of the 

 electrometer if the arc alone was acting. If T was charged nega- 

 tively, then when a current of air was sent between the plates 

 the wire W became charged negatively. If T was charged posi- 

 tively there was no appreciable leak to W. This shows that a 

 negatively charged gas has passed into the cylinder which in the 

 first case lost its charge to the central wire and in the other to 

 the tube T. A very convenient means of testing the whole 

 charge conveyed with the current of air is to place a plug of 

 cotton-wool inside the tube, which has the property of completely 

 discharging the electrification carried with the air. 



