434 Drs. Beattie and De Smolan on the Conductance 



different metals insulated within the unpolished aluminium 

 cylinder as described above. Column III. gives the differ- 

 ences for two of the same metals in the interior but with the 

 surrounding aluminium cylinder altered by its inner surface 

 being polished by emery-paper. 



I. IT. II. 



Insulated metal. 



Magnesium tape — 0*67 L of a volt. 



Amalgamated zinc —0*66 „ 



Polished aluminium .... — 0-465 „ 



Polished zinc -0-343 „ 



Unpolished aluminium . . — 0-349 „ -f-0'35 of a volt. 



Polished lead - 0-257 „ 



Polished copper +0-129 „ 



Polished iron nail +0-182 



Palladium wire +0*255 ,, 



Gold wire +0-264 „ +0-930 „ 



Carbon +0-429 „ 



It will be noticed that the difference of potential depends 

 very much on the state of polish of the two mutually insu- 

 lated conductors. 



To make similar experiments with ultra-violet light we 

 used the brass wire gauze cage arrangement described in § 2. 

 That is, we have now air between the wire gauze and the 

 insulated conductor rendered conductive by ultra-violet light. 

 The insulated conductor was 2 centim. distant from the gauze. 

 The steady electrometer-reading after the two pairs of quad- 

 rants were insulated and the ultra-violet light shining (which 

 we shall hereafter refer to as the ultra-violet-light-zero) was 

 observed. The difference of potential indicated on the elec- 

 trometer between the rays-zero and the metallic zero does not 

 give, however, the contact-force between the gauze and the 

 insulated conductor within. The reason for this we shall see 

 in the next section. 



The following table shows the steady potential-differences 

 in the electrometer due to the conductive effect produced by 

 ultra-violet light in the air between the brass wire gauze and 

 the insulated conductor. 



Insulated metal. Potential-difference. 



Polished zinc —0-75 of a volt. 



Polished aluminium —0*66 „ 



German silver —0-19 „ 



Gilded brass +0-04 



Polished copper +0*12 „ 



Oxidized copper +1*02 „ 



