Proceedings of Royal Society of Edinburgh . 
468 
[SESS. 
block of paraffin. The arrangement will easily be understood from 
the diagram on p. 467. 
In the first instance a piece of lead of the same size as the 
uranium was insulated on paraffin in the metallic cylinder, and 
was connected to the case of the electrometer. The metal cylinder 
was also connected to the electrometer case. Air drawn from the 
cylinder through the filter caused no deviation from the metallic 
zero of the electrometer. When the lead was disconnected from 
the case of the electrometer and joined to one terminal of a battery 
and the other terminal connected to the case of the electrometer 
no electrification of the air was observed with the lead at potentials 
up to ± 95 volts. 
When the uranium was insulated in the metallic cylinder, and 
this latter was of copper polished inside, the following results were 
obtained. 
With uranium and the copper cylinder connected to case of 
electrometer a positive electrification of the air was observed, such 
that an electrometer deviation of + ’05 of a volt was produced per 
minute, the pump being worked at the rate of twelve strokes per 
minute. The uranium was disconnected from the electrometer case 
and joined to one terminal of a battery, the other terminal and the 
copper cylinder being connected to the case of the electrometer. 
The results are given in the following table : — 
Electrometer reading per 
Uranium kept at minute of pumping. 
Twelve strokes per minute. 
+ 2 volts. 
+ -36 of 
a volt. 
+ 10 
5 ) 
+ *65 
33 
+ 22 
33 
+ •53 
33 
+ 45 
53 
+ -35 
33 
+ 68 
39 
+ •25 
33 
+ 93 
39 
+ •235 
33 
- 2 
33 
-•32 
33 
- 10 
33 
-•53 
33 
-22 
33 
-•40 
33 
-45 
33 
-•25 
33 
-68 
33 
- -22 
33 
-93 
53 
-•20 
33 
The uranium and one terminal of the battery were next con- 
