496 BELL SYSTEM TECHNICAL JOURNAL 



In the early Investigations of dielectrics two distinct types of charg- 

 ing current were recognized, the one in which the charging or dis- 

 charging of a condenser occurred practically instantaneously and the 

 other in which a definite and easily observable time was required. A 

 charge accumulating in a condenser in an unmeasurably short time 

 was variously referred to as the instantaneous charge or geometric 

 charge or the elastic displacement. The current by which this charge 

 is formed was called the instantaneous or geometric charging current, 

 and similarly the terms instantaneous dielectric constant or geometric 

 dielectric constant were used to describe the property of the medium 

 giving rise to the effect between the condenser plates. An even wider 

 variety of names has been used for the part of the charge which formed 

 or disappeared more slowly. Among these are residual charge, 

 reversible absorption, inelastic displacement, viscous displacement 

 and anomalous displacement. The modern theory still recognizes 

 these two distinct types of condenser charges and charging currents 

 but the simple descriptive designations rapidly-forming or instantaneous 

 polarizations and slowly-forming or absorptive polarizations will be 

 adopted here, as they seem sufficient and to be preferred to terms 

 which have more specialized connotations as to the mechanism upon 

 which the behavior depends. The properties of these two types of 

 charging currents and the dielectric polarizations corresponding to 

 them appear prominently in the theories of dielectric behavior. 



The total polarizability of the dielectric is the sum of contributions 

 due to all of the different types of displacement of charge produced in 

 the material by the applied field. Constitutive forces characteristic 

 of the material determine both the magnitude of the polarizability and 

 the time required for it to form or disappear. The quantitative 

 measure of the time required for a polarization to form or disappear is 

 called the relaxation-lime. In the following a description will be given 

 of the physical processes involved in the formation of dielectric polari- 

 zations, indicating the effect of chemical and physical structure upon 

 the two quantities, magnitude and relaxation-time, which determine 

 many of the properties of dielectric polarizations of the slowly-forming 

 or absorptive type. 



The magnitude of the polarizability ^ of a dielectric can be expressed 

 in terms of a directly measurable quantity, the dielectric constant e, 

 by the relation 



47r (e -f 2) 

 It is sometimes convenient to use the polarizability and the dielectric 





