1896-97.] J. Carruthers Beattie on Electrification of Air. 471 
uranium were used — uranium acetate and uranium nitrate. The 
nitrate was deposited on a strip of platinum. The platinum was 
then insulated on paraffin in the copper cylinder described above. 
The same series of experiments were gone through, and results of 
the same nature as those described in § 3 were obtained. The 
electrifications of air observed were, however, much smaller in 
amount. The acetate was deposited on tinfoil, and placed in a zinc 
cylinder which was provided with a mica window. By means of 
this window ultra violet light from an arc lamp could be caused to 
shine on the acetate. The electrifications of air were the same in 
kind as those already described, and were of about the same amount 
as those obtained with the nitrate of uranium. When the ultra 
violet light was shone on the acetate the electrification of the air 
produced did not differ from that which was produced with ordi- 
nary light. 
Note by Lord Kelvin on the sign of the electrification found in 
air drawn from space surrounding electrified uranium . 
In some of our previous experiments with high voltages we 
found sparks to pass between uranium and other metals* ap- 
parently according to the laws of disruptive discharge subject to 
but little modification by the special quasi-conductivity induced in 
air by the ‘uranium rays.’ On the other hand, all our experi- 
ments with voltages, less than 500 or 600 volts per cm. of line of 
force in the air at ordinary atmospheric pressure seem to be not 
sensibly influenced by disruptive charges or by brushes ; and the 
quasi- conductivity of air induced by uranium was the dominant 
factor. This is undoubtedly the case in the experiments now 
described by Dr Beattie, and I assume it to be so in what follows, 
except when I give express warning of possible liability to disrup- 
tive discharges. 
The effective conductivity induced in the air by the uranium in- 
fluence is of course greatest in the immediate neighbourhood of the 
uranium, but there is something of it throughout the enclosure. 
Hence it may be expected that electricity of the same kind as that 
of the uranium will be deposited in the air close around it, and 
electricity of the opposite kind in the air near the enclosing metal 
* Kelvin, Beattie, and Smolan, Proc. R.S.E . , 1897. 
