SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 4G9 



. different lines of thought. One holds that the heterogeneity of the 

 dielectric is the cause of residual charge, and this theory has been 

 developed by Maxwell and Rowland. The second ascribes the greatest 

 importance to the elastic properties of the dielectric in the formation 

 of residual charges. Hopkinson developed a theory of residual charge 

 analogous to Boltzmann's theory of elastic after-effects, but this is too 

 general to be of practical use. Of the many other later theories which 

 take account of the elasticity of the dielectric, the one formulated by 

 Houllevigue 1 seems to be the most promising. He gets a fairly simple 

 solution of his differential equation for the current flowing into a con- 

 denser during a continuous charging. This current is made up by 

 superposing the ordinary, practically instantaneous, charging current 

 upon the slower residual forming current, which lasts for an appreci- 

 able interval of time. This latter current is considered to be due to a 

 slow displacement of a part of the ether, being conditioned by the 

 molecules of the dielectric. 



In recent years the questions of " viscous dielectric hysteresis " or 

 "lagging polarization," and of "energy losses " in the dielectric, have 

 claimed much attention among physicists, and for a considerable time 

 the problem of residual charge was completely overshadowed by these 

 later questions. Some energy is undoubtedly lost in the form of heat 

 in the dielectric, when the electric force is continually varied, as in an 

 alternating current or a rotating electrostatic field. It is still an open 

 question whether this loss of energy is chiefly to be associated with 

 Joulean heat production in the dielectric, or with a viscous lag of the 

 dielectric polarization behind the polarizing force. Each side of the 

 question has found numerous and able supporters. It is greatly to.be 

 desired that a conclusive answer be obtained as soon as possible, for the 

 subject is not only of immense practical importance in all telegraphy, 

 telephony, and electrical engineering practice, but has undoubtedly very 

 close relations to the problem of the ultimate constitution of matter. In 

 fact the question of dielectric viscosity, or energy losses in dielectrics, 

 seems to be an important part of electric dispersion, a subject which is 

 just now receiving considerable attention. 



The latest development of these very interesting questions of die- 

 lectric viscosity and energy losses seems to be a reopening of the 

 older problem of residual charge formation. Indeed some of the most 

 recent writers on the subject, especially E. R. von Schweidler, 2 appar- 



1 Ann. de l'Univ. de Lyons, 32 (1897); J. de Phys., 6, 113-120, 120-126 

 (1897). 



2 Ann. der Phys., 24, 711 (1907). This paper gives an excellent bibliog- 

 raphy of the subject. 



