24:2 Mr. Norman Shaw on Charged Surface Layers in 



method of detecting these layers in a direct manner, and 

 of getting further information concerning their nature. 

 Erskine-Murray *, Greinacherf, and Anderson and BowenJ 

 have shown experiments in which an insulated plate placed 

 near another plate which is earthed assumes, whenever the 

 intervening gas is ionized, a difference of potential equal to 

 the contact potential between the two plates. This effect is 

 analogous to that obtained by connecting two different 

 metals with a drop of an electrolyte, and it was thought that 

 zl further study of the rate at which this potential was 

 assumed might be profitable. 



§ 1. Apparatus. 



After several preliminary experiments had been performed, 

 "the apparatus shown in fig. 1 was constructed for the 



investigation. 



To POTENTIA 

 ■ DIVIDER OR TO EARTH 



Fig. 1. 



TGFOTENTlnL DIVIDER.OR TO E#PTH 



To Dffnnc tubes etc 



POTENTIAL DIVIDE fi C Vf TO EARTH 



To PUMP 



TO ELECTROMETER 



A is a brass cylindrical vessel (12 cm. x 10 cm.) resting 

 •on insulating supports, II. Its side can be removed by 

 sliding vertically, and the top of the vessel is supported on 



* Erskine-Murray, Proc. Roy. Soc. vol. lix. p. 333 (1896). 

 t Greinacher, Ann. de Phys. vol. xvi. p. 708 (1905). 

 X Anderson and Bowen, Proc. Phys. Soc. Lond. vol. xxiii. p. 310 

 <1911). 



