Electricity by Radium and Thorium Emanations. 461 



has shown that both polonium and radium give out quantities 

 of these rays ; at distances from the active matter exceeding 

 a few millimetres they are found to have entirely neutralized 

 the charge on the a, particle. Prof. Thomson suggests that 

 these rays may also be emitted by the emanations of radium 

 and thorium (though they have been shown to give out no 

 rapidly-moving ft rays) ; and that if this is the case, it may 

 offer an explanation of the deposition of excited activity on 

 the negative electrode. The experiments described in this 

 paper were undertaken in order to decide this point. 



The method of experimenting and the apparatus employed 

 were essentially the same as those used by Prof. Thomson 

 (ng. 1). 



Ksr. 1. 



The inner surface of the bulb A (7 cm. in diameter) was 

 silvered over, and kept connected through the terminal E to 

 earth. B is a gold-leaf electroscope, mounted on a quartz 

 rod C, and charged by contact with the wire ¥, which is then 

 earthed. The wire D throughout each observation was kept 

 at the potential to which B was initially charged, thus acting 

 as a guard-ring. In the side-tube Gr was placed a small 

 quantity of impure radium bromide; H contained hard 

 charcoal, and could be immersed in liquid air, in order to get 

 as good a vacuum as possible. 



The apparatus was exhausted to the best vacuum obtainable 

 on the pump, and then sealed off and set up with the tube H in 

 liquid air. The gold-leaf was then charged, and its rate of 



