1897-98.] 
Electric Equilibrium of Uranium. 
131 
On Electric Equilibrium between Uranium and an Insu- 
lated Metal in its Neighbourhood. By the Rt. Hon. 
Lord Kelvin, G.C.V.O., P.R.S.E., &c. ; J. Carruthers 
Beattie, D.Sc., F.R.S.E. ; and M. Smoluchowski de 
Smolan, Ph.D. 
(Read March 1, 1897.) 
[Accidentally omitted from Proc. Roy. Soc. Edin. for Session 1896-7, p. 417, 
but published in Nature for March 11, 1897.] 
The wonderful fact that uranium held in the neighbourhood 
of an electrified body diselectrifies it was first discovered by 
H. Becquerel. Through the kindness of Prof. Moissan we have 
had a disc of this metal, about 5 cm. diameter and J cm. thickness, 
placed at our disposal. 
We made a few preliminary observations on its diselectrifying 
property. We observed first the rate of discharge when a body 
was charged to different potentials. We found that the quantity 
lost per half-minute was very far from increasing in simple propor- 
tion to the voltage, from 5 volts up to 2100 volts; the electrified 
body being at a distance of about 2 cm. from the uranium disc. 
[Added March 9, 1897. — We have to-day seen Prof. Becquereks 
paper in Comjjtes Rendus for March 1. It gives us great pleasure 
to find that the results we have obtained on discharge by uranium 
at different voltages have been obtained in another way by the dis- 
coverer of the effect. A very interesting account will be found in 
Prof. Becquereks paper, which was read to the French Academy of 
Sciences on the same evening, curiously enough, as ours was read 
before the Royal Society of Edinburgh.] 
These first experiments were made with no screen placed between 
the uranium and the charged body. We afterwards found that 
there was also a discharging effect, though much slower, when the 
uranium was wrapped in tinfoil. The effect was still observable 
when an aluminium screen was placed between the uranium, 
wrapped in tinfoil, and the charged body. 
