24cG Mr. Norman Shaw on Charged Surface Layers in 



plates which had been polished. A lead plate was placed in 

 the apparatus as the plate C; dry air was passed through for 

 some hoars ; and the vessel A was then sealed. Three sets 

 of special observations, (a), (6), and (c), were taken as out- 

 lined below, with the plates at a distance of 8 millimetres* 



Fi<>\ 2. 



0-050!- 



o-oco 



15 30 45 60 75 90 105 



135 150 165 



195 210 225 240 Seconds 



The conditions of ionization in the vessel A were constant, 

 and throughout the set there was no change in the circuit 

 which could involve a change in capacity as ordinarily 

 produced. 



(a) The plates and vessel A were earthed for some time ; 

 then the lead plate C, together with the quadrants to which 

 it was connected, were insulated, and found to assume 

 gradually a difference in potential from the brass equal to 

 the contact difference, at a rate given by the curve (a) in 

 tig. 2. The constancy with which these figures could be 

 repeated is shown in Table I. 



(b) After the electrometer reading had become steady the 

 brass plate B and also the vessel A were charged to a 

 potential equal and opposite to the contact potential between 

 brass and the plate C. The reading then returned to zero, as- 



