470 Proceedings of Royal Society of Edinburgh. [sess. 
effects were less than those obtained with the uranium alone. For 
example, with the aluminium-foiled uranium kept at + 2 volts and 
the lead cylinder to case ; or with first to case and cylinder at - 2 
volts, the electrification of the air drawn through the filter caused 
an electrometer deviation of + T1 of a volt per minute of pumping. 
With +10 volts the electrometer deviation was + 0'05 per minute 
with +95, + *015 of a volt per minute. The negative electrifica- 
tions of the air with the uranium kept at - 2, - 10, or at 95 volts 
and the metallic cylinder to the case of the electrometer were 
smaller than the corresponding positive electrification. 
Finally, the uranium was placed inside a paraffin cylinder. 
Round the outside of this cylinder tinfoil was wrapped. With 
both uranium and tinfoil connected to case, the air drawn from the 
cylinder showed no signs of electrification. With the uranium 
positively or negatively electrified, the air was found to be positively 
or negatively electrified. The amount of the electrification for any 
given voltage depended, however, on the order in which the 
voltages were taken. For example, after the tinfoil wrapped 
round the paraffin cylinder had been connected to the positively 
electrified terminal of the battery and the uranium to case, it was 
found that the air drawn through the filter caused an electrometer 
deviation of - ‘235 of a volt per minute. In the succeeding six 
minutes, while the tinfoil was kept at 10 volts and the uranium 
connected to case, the electrometer deviation was + *7 of a volt 
per minute. In the next two minutes it was + ‘6 of a volt per 
minute, and six minutes later it was + ‘3 of a volt. Both uranium 
and tinfoil were next connected to case, and in the first two minutes 
there was an electrometer deviation of - ‘6 of a volt per minute of 
pumping. In the second two minutes this deviation fell to - T3 
of a volt per minute. With the uranium connected to case and the 
tinfoil kept at a potential of +10 volts, the air was found to be 
negatively electrified, the amount of this electrification decreased in 
10 minutes from- *65 of a volt in the first minute to - ‘2 of a 
volt in the tenth minute. On again connecting both uranium and 
tinfoil to case, the air was found to be + ly electrified : the deviation 
obtained in the first minute was+ ‘65 of a volt, in the 8th + ‘15 of 
a volt. 
§ 4. Electrification of air by uranium salts. — Two salts of 
