1891.] On Electrical Evaporation. 97 



upon. The apparatus was similar to that used for the cadmium 

 experiments (fig. 7). Small lumps of pure silver were cast on the 

 ends of platinum wires, and suspended to the inner ends of platinum 

 terminals passing through the glass bulb. The platinum wires were 

 protected by glass, so that only the silver balls were exposed. The 

 wliole apparatus was enclosed in a metal box lined with mica, and 

 the temperature was kept as high as the glass would allow without 

 softening. The apparatus was exhausted to a dark space of 3 mm., 

 and the current was kept on for 1-g- hours. The weights of silver, 

 before and after the experiment, were as follows : 



Positive pole. Negative pole. 



Original weight of silver 18'14 grs. 24'63 grs. 



Weight after the experiment 18'13 24'44 



Silver volatilised in 1J hours O'Ol 0'19 



It having been found that silver volatilised readily from the 

 negative pole in a good vacuum, experiments were instituted to ascer- 

 tain whether the molecules of metal shot off from the pole were 

 instrumental in producing phosphorescence. A glass apparatus 

 was made as shown in fig. 9. A pear-shaped bulb of German glass 



has, near the small end, an inner concave negative pole, A, of pure 

 silver, so mounted that its inverted image is thrown upon the opposite 

 end of the tube. In front of the pole is a screen of mica, having a 

 small hole in the centre, so that only a narrow pencil of rays from the 

 silver pole can pass through, forming a bright spot of phosphor- 

 escence, D, at the far end of the bulb. The exhaustion was pushed 

 to a high point, O00068 mm., or O9 M. The current from an induc- 

 tion coil was allowed to pass continuously for some hours, the silver 

 VOL. L. H 



