ELECTRIFICATION OP AIR, VAPOUR OF WATER, AND OTHER GASES. 217 



70. We then tried as filters tubes of different materials, but all of the same 

 length (10 centims.), and bore (0'91 centim.). Glass, brass, block tin, copper, and 

 zinc were used : the glass tube was covered externally with tin-foil, and also a little 

 way inside at each end. As usual, the air in the can was charged from the insulated 

 needle point at 4000 volts positive, and 3200 volts negative (74), and drawn off through 

 340 centims. of block-tin pipe of 0'91 centim. bore, extending from the centre of the 

 can to the insulated filter, which was either glass, brass, or block tin. Before testing 

 the copper and zinc tubes, the can was brought nearer to the electrometer, so that 

 the length of the block-tin pipe conveying the electrified air to the filter was reduced 

 from 340 centims. to 100 centims. The mean of a large number of tests gave the 

 following deflections for 6 strokes of the pump in 1 minute, the mean result in every 

 case being very similar to the individual results. 



Deflection per C strokes of pump. 



Positive. 



I'l mean of 3 experiments 

 1-4 -2 



3-3 2 

 G-3 ,. 4 



8-4 G 



Negative. 



7'0 mean of 3 experiments 

 *8 2 

 3-1 2 

 3-0 3 

 2-3 I! 



71. The zinc filter was the only one which showed a distinctly greater deflection 

 for positive than for negative electricity, a result which is opposite to one obtained by 

 RUTHERFORD, * experimenting with air which had been electrified from an electrified 

 body under the influence of E.OXTGEN rays. The previous experiments having shown 

 that, on drawing electrified air over the insulated and non-electrified solid brass 

 cylinder with rounded ends, the cylinder extracted from the air a large proportion of 

 its charge, we now arranged to charge the cylinder and draw non-electrified air over 

 it to the standard insulated filter connected with the electrometer, to see if the air 

 would take up from the cylinder a part of its charge. The arrangements were as 

 shown in fig. 9. The cylinder was charged positively and negatively at potentials 

 varying from 1000 volts to 15,000 volts, but no trace of electrification of the air after 

 passing over the brass cylinder could be detected. 



The Effects of the Uranium "rays," discovered by BECQUEEEL, and of a Candle 



Flame, on Electrified Air. 



72. The air in the can (fig. 8) was charged in the usual way by a needlepoint 

 at 3200 volts negative for 1 minute, and the electric machine was then stopped ; the 





VOL. CXCI. A, 



* See 'Phil. Mag.,' April, 1897, p. 246. 

 2 F 



