1896 - 97 .] J. Carruthers Beattie on Electrification of Air. 469 
nected to the case of the electrometer, and the copper cylinder 
joined to the other terminal. With this arrangement it was 
found that there was a negative electrification of the air with the 
positive terminal connected to the copper cylinder, and a positive 
electrification with the negative terminal connected to the same 
cylinder; the amounts of these electrifications per minute were 
exactly equal to the electrification of the same sign when the 
uranium was connected to the battery and the cylinder to the case. 
Thus, with the cylinder at + 22 volts, a negative electrification of 
the air was produced, which gave a deviation on the electrometer 
per minute of pumping equivalent to - '40 of a volt. 
The same results were obtained after the inside surface of the 
copper cylinder had been oxidised. 
With the uranium insulated in a zinc cylinder and with uranium 
and cylinder connected to case, an electrometer reading equal to 
— 0T of a volt per minute of pumping was observed. With an 
aluminum cylinder and the same connections a slight positive 
electrification of the air was observed. With a lead cylinder a 
negative electrification of - '05 of a volt per minute was found. 
The results obtained when the uranium was kept at a definite 
potential and the cylinder connected to case were the same as in 
the experiments with the copper cylinder. 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, negatively 
when the uranium was electrified negatively, and always, for a 
given positive potential of the uranium, the air was electrified more 
strongly positive than it was negative for a like negative potential 
of the uranium. The electrification of the air attained a maximum 
when the uranium was charged to a potential between ±10 and 
±22 volts. 
The uranium was next wrapped in aluminium foil and again 
insulated in the lead cylinder. The air drawn away from the 
cylinder was found to be negatively or positively electrified 
according as the aluminium-foiled uranium was negatively or 
positively electrified. The maximum electrification of air was 
obtained with the covered uranium charged to about 6 volts. The 
