470 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ently consider that both "viscous hysteresis" and "energy losses" 

 are nothing more than results of the older phenomenon of residual 

 charge formation, and are most satisfactorily explained in terms of it. 

 Residual charge had been considered to be only a slow after effect of 

 dielectric polarization, and almost every one who dealt with the subject 

 tacitly assumed that the residual forming current is negligibly small 

 during the charging of the condenser, so that no residual charge worth 

 mentioning forms, say, in one thousandth, or even one hundredth, of a 

 second after the charging voltage is applied. This assumption explains 

 why nearly all investigators of residual charge, except some of very 

 recent years, thought it unnecessary to make their charging times and 

 short-circuit times extremely short, or even to measure or to estimate 

 them. Even the wording of the " laws " which have been stated is 

 very indefinite, as they speak of " instantaneous charges " and " in- 

 stantaneous short circuits " if they attempt to define these time- 

 intervals at all. 



The present research started out with an attempt to test for the 

 presence of an appreciable lag of polarization in paraffin paper con- 

 densers. The effect observed was, however, found to be due to a resid- 

 ual charge formation occurring in less than one tenth of a second, and I 

 was led to an extensive investigation of the rate of residual charge 

 formation at times as near to the instant of beginning the charging of 

 a condenser as it was possible to obtain with the apparatus employed. 



Neglecting for the moment various results of secondary importance, 

 1 wish to describe in detail in this paper three things which I hope 

 will prove to be of some interest and value as contributions to the 

 scientific study of dielectrics : 



First, a method of studying the rate of formation of residual charge 

 during very short charging intervals. This is a differential, or second 

 order, method, and is capable of a very high degree of accuracy. Its 

 great advantage is that it measures all the residual charge formed, no 

 charge being lost in the process of short-circuiting the condenser. 



Secondly, the best results of many observations on various dielectrics 

 embodied in a series of curves, which although only first approxima- 

 mations, give correctly the general character and magnitude of the 

 residual forming current for the time interval 0.00007 to 0.00170 of a 

 md during which the charging voltage has been applied. These 

 results show that the residual charge formed in this very short time 

 is considerable in condensers made of paraffined paper and glass, and 

 appreciable even in mica condensers. 



Thirdly, a process for preparing with the greatest ease sheets of 

 pure paraffin of almost any desired thinness, to be used in building up 



