Induced-Radioactivity in Air. 355 



smaller than if the rod had been electrified in the open air, 

 I tried the effect of increasing the current by ionizing the 

 gas in the tank by means of Rontgen rays : the tube giving 

 out the rays was placed outside the tank, the rays passing 

 into the tank through the millboard cover; this had, of course, 

 the effect of greatly increasing the saturation-current through 

 the tank, and it was found that now prolonged negative 

 electrification of the rod produced an appreciable effect; the 

 saturation-current, when the rod which had been negatively 

 electrified in the tank was used as electrode, was considerably 

 larger than when the electrode was a rod which had not been 

 so treated. The magnitude of the effect is indicated by the 

 numbers given below, which represent the deflexions of the 

 electrometer in one minute ; these numbers are proportional 

 to the saturation-current: — 



Current at 11 A.M. with rod (1) as electrode ... 74 

 Current at 5 p.m. after rod (1), which remained in 

 the tank, had been attached to the negative ter- 

 minal of a Wimshurst machine while the gas in 

 the tank was ionized by Rontgen rays. 

 Current at 11 A.M. with red (2) as electrode ... 74 

 Current at 5 p.m. with rod (2) as electrode, this rod 

 having been exposed to the air of the room and 

 connected with the negative terminal of a Wims- 

 hurst machine. 



Current at 11 a.m. with rod (3) as electrode ... 72 

 Current at 5 p.m. with rod (3) as electrode, this rod ^ 

 having been exposed to the air of the room and I 71 

 connected with the positive terminal of a Wiins- | 

 hurst machine. J 



The above experiments were made on the same day. We see 



that with the negatively electrified rod in the tank there was 



an appreciable increase ; in the case of the other rods the 



changes were too small to allow any conclusions to be drawn. 



A considerable number of experiments of this type were 



made : it will be sufficient to give one more example : — 



Current at 11 a.m. with rod (1) as electrode ... 77 



Current at 5 p.m. with rod (1) as electrode, the rod 



having been in the tank in the interval, connected 



with the negative terminal of a Wimshurst 



machine and the air ionized by Rontgen rays. 



Current at 11 A.M. with rod (2) as electrode . . . .76 



Current at 5 P.M. with rod (2) as electrode, the rod 1 



having been kept in the tank but not electrified > 74 



in the interval. J 



86 



76 



