CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



RESIDUAL CHARGES IN DIELECTRICS. 



By C. L. B. Shuddemagen. 



Presented by B. 0. Peirce, November 11, 1908. Received January 21, 1909. 



Introduction. 



The curious phenomenon of the residual charge which appears after 

 a discharge by a momentary short circuit in a condenser which has a 

 solid dielectric was observed as early as 1768 by Franklin, in the 

 case of a glass " Franklin's plate " ; but systematic research into the 

 laws governing the formation and liberation of residual charge did not 

 begin until about 1854, when R. Kohlrausch published the first impor- 

 tant article on the subject. Up to that date it was the common belief 

 that electric charge actually penetrated from the armatures of a 

 charged condenser into the dielectric substance, from which it slowly 

 returned to the armatures after each momentary discharge. The 

 results of Kohlrausch showed, however, when viewed in the light of 

 the theory of electric potential, that the penetration hypothesis was 

 unsound, and that the true explanation was to be looked for in a 

 polarized state of the molecules in the dielectric, in accordance with 

 Maxwell's theory. Kohlrausch laid down the following two fundamen- 

 tal laws governing residual charge formation : 



1. The actual charge which can be drawn instantaneously from a 

 charged condenser is at all times proportional to the potential difference 

 of the condenser terminals. 



2. In the same condenser the residual charges formed during equal 

 times after charging are propwtiotial to the initial charges, or the 

 charging potentials. 



If the penetration hypothesis were correct, then during a momen- 

 tary short circuit of a charged condenser charges of opposite sign 

 should flow on to the condenser armatures in order to neutralize the 

 potential of the charges which penetrated a short distance into the dielec- 

 tric ; while according to Kohlrausch's views the polarization of the 

 molecules in the dielectric has the effect of neutralizing the potentials 



