580 Prof. F. T. Trouton and Mr. S. Russ on the Rate of 



Rate of Recovery , or Current at Constant Difference 

 of Potential. 



In these experiments a constant difference of potential 

 was maintained between the two coatings of the condenser, 

 and the rate at which the Residual Charge leaked out under 

 these conditions was found. 



It is clear that if a constant deflexion on the scale of the 

 electrometer can be maintained while the Residual Charge is 

 appearing, then a constant difference of potential exists 

 between the coatings of the condenser. 



This constant potential-difference was maintained by the 

 use of a variable resistance obtained by connecting the two 

 coatings of the condenser to two parallel plates of tin, 

 on one of which a thin layer of uranium fluoride, for the 

 purpose of producing the necessary ionization of the air 

 between the plates, was uniformly sifted. Owing to the dif- 

 ference of potential between these plates there will be a 

 gradual leak of the residual charge across the air-gap between 

 them, and if the effective area of the uranium surface can be 

 adjusted the value of this current can be controlled as required. 

 The effective area of the air conductor was regulated by a 

 movable shutter which was made to slide in between the 

 two parallel plates, thus curtailing the active area of the 

 uranium fluoride surface and thereby the cross section of our 

 conductor. 



The mode of carrying out an experiment was to allow the 

 difference in potential between the plates of the condenser to 

 rise through the development of residual charge, to a certain 

 selected value, and then to prevent further increase by con- 

 necting them through the variable ionized air-resistance. 

 To preserve this constancy in potential the shutter must bo 

 continuously pushed in so as to diminish the current at the 

 proper rate, namely, that at which the residual charge is 

 developed by the unstraining dielectric. 



The position of the shutter at any moment while being 

 pushed in so as to keep the deflexion of the electrometer 

 constant, could be readily found : this is a measure of the 

 current or the rate at which the charge comes out of the 

 condenser when a constant potential-difference is maintained 

 between its coatings. 



A " hand " method was first tried for closing the shutter. 

 The apparatus used is indicated in fig. 1. K a condenser of 1 

 mica plates was first charged by a series of cells C for a 

 definite interval of time (1-J mins.), discharged through the 

 key B, and its two coatings were then connected to the elec- 



