436 Drs. Beattie and De Sinolan on the Conductance 



The great effect of the surfaces as to polish is very evident 

 in the above table. 



With a third specimen of oxidized copper a potential-differ- 

 ence of +0*35 of a volt was obtained. This specimen was 

 afterwards connected to the case of the electrometer ; a piece 

 of polished aluminium was placed opposite it and connected 

 to the insulated terminal of the electrometer. The uranium 

 disk, insulated on paraffin, was then placed between them, and 

 the deviation observed was equivalent to a potential-difference 

 of —1*53 volts ; that is, we obtained an effect equal to the 

 sum of the effects we obtained when the metals were separately 

 insulated in air opposite uranium. 



Instead of placing the uranium directly opposite the insu- 

 lated metal in air, we also observed the uranium-zero by 

 mutuallv insulating two metals in air, one of which was 

 transparent to the uranium influence. 



For this purpose we made a tinfoil box with tinfoil suffi- 

 ciently thin to be transparent to the uranium influence. The 

 tinfoil forming the box was connected to the electrometer- 

 case. 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 uranium-zero was obtained 

 whether the uranium was insulated or connected to the case 

 of the electrometer. The time required to reach the uranium- 

 zero with this arrangement was usually four or five minutes. 

 A charge given to the insulated metal large enough to pro- 

 duce a deviation beyond the uranium-conductance-zero was 

 discharged till this zero was reached. A charge causing the 

 electrometer-reading to deviate in the opposite direction was 

 discharged to the metallic zero and thence on to the uranium- 

 conductance-zero, where it remained steady. 



§ 8. Dependence of the Difference of Potential as measured 

 in § 7 on distance between the two mutually insulated con- 

 ductors. 



A cardboard box, 46 centim. long, 19 centim. square (see 

 fig. 10), lined with tinfoil, connected to the case of the electro, 

 meter was used. Inside this box an insulated disk of oxidized 

 copper 10 centim. diameter was supported in such a way as 

 to allow of its being fixed at different distances from the tin, 

 foil-coated end-wall of the box, facing it. Two windows were 

 cut in the side of the box as shown in the diagram. The 

 Rontgen lamp was placed outside the box at the line joining 

 the windows. These windows were covered with tinfoil gauze 



