1896 - 97 .] J. Carruthers Beattie on Electrification of Air. 467 
When the electrodes were drawn so far apart that sparking did 
not take place, air drawn from the positive electrode raised the 
filter to a potential of + ’7 of a volt after one minute’s pumping ; 
air drawn from the neighbourhood of the negative electrode gave 
a reading of — 1 *5 of a volt in the same time. 
When the negative electrode was connected to the cathode of a 
Crookes’ tube, air drawn from the immediate neighbourhood of 
the cathode through the filter caused an electrometer deviation 
equivalent to a potential of - '8 of a volt. Air drawn from the 
immediate neighbourhood of the wire connecting the negative 
electrode to the cathode caused a deviation equivalent to - *7 of 
a volt. Air drawn from the neighbourhood of the anode or of the 
wire connecting the anode to the positive terminal of the coil gave 
a positive reading on the electrometer less in amount than the 
corresponding negative reading. 
§ 3. Electrification of air by metallic uranium. To examine the 
electric state of the air in the neighbourhood of metallic uranium 
charged to a given potential, the following experimental arrange- 
ment was made. A metallic cylinder, 24 cms. length, 8 cms. 
diameter, was constructed. One end of this was closed with a 
piece of the same metal ; in this end was a hole into which a plug 
of tunnelled paraffin was placed ; from the paraffin a piece of india- 
rubber tubing about feet long led to the electric filter. The 
other end of the metallic cylinder was closed with a disc of paraffin, 
in the centre of which a hole was made to admit air from the 
laboratory. This hole was filled with cotton wool. The metallic 
uranium, 5'5 cm. diameter, - 5 cm. thickness, was insulated on 
paraffin inside the cylinder. The cylinder itself was laid on a 
