1896 - 97 .] Experiments on Electric Properties of Uranium. 419 
of +0‘35 of a volt was obtained. This specimen was afterwards 
connected to sheaths; a piece of polished aluminium was placed 
opposite it and connected to the insulated terminal of the electro- 
meter. The uranium disc, insulated on paraffin, was then placed 
between them, and the deviation observed was equivalent to a 
potential difference of - T53 volts; that is, we obtained an effect 
equivalent to the sum of the effects we obtained when the metals 
were separately insulated in air opposite uranium. 
§ 26. Instead of placing the uranium directly opposite the 
insulated metal in air we also observed the conductance-zero by 
mutually insulating two metals in air, one of which was transparent 
to the uranium influence. 
For this purpose we made a tinfoil box, with tinfoil sufficiently 
thin to be transparent to the uranium influence. The tinfoil 
forming the box was connected to sheaths. Inside it another 
metal was insulated on a glass stem, and placed so as to be parallel 
to one end of the tinfoil box. This metal was connected to the 
insulated terminal of the electrometer. The uranium was placed 
outside the box, about half a centimetre distant from the end to 
which the insulated metal was parallel. The same conductance- 
zero was obtained with the uranium insulated, or with it connected 
to sheaths. The time required to reach the uranium-conductance- 
zero with this arrangement was usually four or five minutes, and 
charge given to the insulated metal large enough to produce a 
deviation beyond the conductance-zero was discharged till this 
zero was reached. A charge, causing the electrometer to deviate 
in the opposite direction, was discharged to the metallic zero and 
thence on to the uranium-conductance-zero, where it remained 
.steady. 
With polished aluminium as the insulated metal, the potential 
difference obtained was — 0'7 of a volt. 
§ 27. Effect of various screens on the rate of reaching the zero. — 
With the second arrangement, described in § 25, it was possible to 
obtain a relative idea of the transparency to the uranium effect 
of screens of various materials. For example, when a sheet of 
lead, about 2 mms. in thickness, was placed between the uranium 
and the tinfoil, no deviation from the metallic zero was obtained. 
In other words, lead is not transparent to the uranium influence. 
