Air by Uranium and its Compounds. 105 



(c) Uranium and one terminal of battery connected to the 

 electrometer sheaths, copper cylinder connected to the other 

 terminal of the battery. 



With this arrangement it was found that there was a negative 

 electrification of the air with the positive terminal to the 

 copper cylinder. The deviation on the electrometer per 

 minute of pumping was exactly equal to the negative electri- 

 fication obtained with arrangement (b) with the uranium kept 

 connected to tbe negative terminal of the battery and the 

 positive terminal to sheaths. With the negative terminal to 

 the copper cylinder the air was found to be positively 

 electrified and to the same extent as the corresponding 

 positive electrifications in arrangement (b). 



Similar results were obtained after the inside of the copper 

 cylinder had been oxidized. 



With a zinc cylinder and with the same connexions as in 



(a) an electrometer reading equivalent to —0*1 of a volt per 

 minute of pumping was observed. 



With an aluminium cylinder and arrangement (a) a slight 

 positive electrification of the air was observed. With a lead 

 cvlinder a negative electrification of — "05 of a volt per 

 minute of pumping was obtained. The various cylinders 

 were all of the same size. 



With zinc, aluminium, or lead cylinder and arrangements 



(b) and (c), similar results were observed. That is, the nature 

 of the metal of the vessel surrounding the uranium did not 

 influence the extent to which the air was electrified. 



In all cases the air in the metallic cylinder was electrified 

 positively when the uranium was electrified positively ; nega- 

 tively when the uranium was electrified negatively. The 

 positive electrification given to the air for a given positive 

 potential of the uranium or an equal negative potential of the 

 metallic cylinder was always greater than the negative 

 electrification of the air when the uranium was kept at the 

 corresponding negative potential or the copper cylinder at 

 an equal positive potential. The electrification of the air 

 attained a maximum when the potential was between +10 

 and + 22 volts. These results may be compared with the 

 results obtained with Rontgen rays by Mr. Rutherford *. 

 The explanation of the kind of the electrification of the air, 

 and of the fact that a maximum value is reached, is given in 

 Lord Kelvin's note appended below. 



The uranium was next wrapped in aluminium foil, and 



again insulated in the lead cylinder. The air drawn away 



from the lead cylinder was found to be negatively or positively 



electrified according as the uranium wrapped in aluminium 



* Phil. Mag-. April 1897. 



