132 Proceedings of Royal Society of Edinburgh. [sess. 
To make experiments on the electric equilibrium between ura- 
nium and a metal in its neighbourhood, we connected au insulated 
horizontal metal disc to the insulated pair of quadrants of an elec- 
trometer. We placed the uranium opposite this disc and connected 
it and the other pair of quadrants of the electrometer to sheaths. 
The surface of the uranium was parallel to that of the insulated 
metal disc, and at a distance of about 1 cm. from it. It was so 
arranged as to allow of its easy removal. 
With a polished aluminium disc as the insulated metal, and 
with a similar piece of aluminium placed opposite it in place 
of the uranium, no deviation from the metallic zero was found 
when the pairs of quadrants were insulated from one another. 
With the uranium opposite the insulated polished aluminium, a 
deviation of - 84 scale-divisions from the metallic zero was found 
in about half a minute. [Sensibility of electrometer 140 scale- 
divisions per volt.] After that, the electrometer-reading remained 
steady at this point, which we may call the uranium rays-zero 
for the two metals separated by air which was traversed by ura- 
nium rays. If, instead of having the uranium opposite to the 
aluminium, with only air between them, the uranium was wrapped 
in a piece taken from the same aluminium sheet, and then placed 
opposite to the insulated polished aluminium disc, no deviation 
was produced. Thus in this case the rays-zero agreed with the 
metallic zero. 
With polished copper as the insulated metal, and the uranium 
separated only by air from this copper, there was a deviation of 
about + 10 scale-divisions. With the uranium wrapped in thin 
sheet aluminium, and placed in position opposite the insulated 
copper disc, a deviation from the metallic zero of +43 scale- 
divisions was produced in two minutes, and at the end of that 
time a steady state had not been reached. 
With oxidised copper as the insulated metal, opposed to the 
uranium with only air between them, a deviation from the metallic 
zero of about +25 scale-divisions was produced. 
When the uranium, instead of being placed at a distance of 
1 cm. from the insulated metal disc, was placed at a distance 
of 2 or 3 mm., the deviation from the metallic zero was the 
same. 
