produced in Gases by Rontgen Rays fye. 435 



When the insulated metal was charge.] either positively 

 or negatively and the ultra-violet light let fall on it, the 

 electrometer-reading deviated until the ultra-violet-light-zero 

 was reached. The rate of deviation was the same for a posi- 

 tive or a negative charge if we reckon the charge from the 

 ultra-violet-light-zero. 



We have used two different methods to measure the poten- 

 tial-difference between wires of the same metal connected to 

 two mutually insulated metals when the air between them is 

 rendered conductive by the presence of uranium. The more 

 convenient method is to take uranium as one of the mutually 

 insulated metals. To do this we fixed a metallic disk, 3 

 centim. diameter, to the insulated terminal of the quadrant- 

 electrometer. Opposite this disk, and separated from it by air, 

 we placed the disk of uranium, 5\5 centim. diameter, con- 

 nected to the case of the electrometer. With this arrangement 

 we found, after contact between the quadrants was broken at 

 the electrometer, a deviation from the metallic zero. This 

 deviation took place gradually till a steady reading was reached. 

 This steady reading we shall call the uranium-conductance- 

 zero, or shortly the uranium- zero. If the insulated conductor 

 had a charge given to it of such an amount as to cause the 

 electrometer- reading to deviate from the metallic zero beyond 

 the uranium-zero, the reading quickly fell to this conductance 

 zero and there remained steady. Whon no charge was given 

 to the insulated metal the steady uranium-zero was reached 

 in about half a minute. 



The following table gives the potential-differences found in 

 this way : — 



yr , i Potential-difference, 



in volts. 



Polished aluminium (1) immediately 1 _,-„ 



after being polished J 



Polished aluminium (1) next day . . . , —0-90 



Polished aluminium (2) — 1*00 



Amalgamated zinc — 0*80 



Polished zinc — 071 



Unpolished zinc —0*55 



Polished lead - 0-5 4 



Tinfoil -0-49 



Unpolished aluminium (1) —0*41 



Polished copper —0*17 



Silver coiu +0-05 



Unpolished copper +0-07 



Carbon + 0*20 



Oxidized copper (a) +0-42 



Oxidized copper (b) +0 90 



