SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 471 



condensers of considerable capacity. Three condensers thus built up 

 showed practically no residual charge, even when tested by the sensi- 

 tive method used in this investigation. 



Preliminary Experiments with Electrostatic Voltage Cycles. 



The results of some experiments conducted in the fall of 1907 with 

 the view of testing for a possible lag of polarization were of value to 

 the writer only because they led him to investigate the rate of forma- 

 tion of residual charge for very short times after the charging. How- 

 ever, a brief description of the method employed may not be without 

 some interest. 



By means of two wooden arms, which swept contact brushes over 

 two rows of copper plugs connected to sections of a storage battery of 

 fairly high voltage (say 800), two condensers of very nearly equal 

 capacities were simultaneously charged to the same final potential, 

 then by an electromagnetic device immediately discharged against each 

 other, and the charge left over was then sent through a ballistic gal- 

 vanometer and measured. In this process both condensers were charged 

 by increasing the voltage by steps of 30 or 60 volts, but one was charged 

 to the final voltage by stopping its arm over any desired plug, while 

 the other was charged up to say 420 volts, then decreased by steps 

 until the voltage was again equal to that of the first condenser. I 

 thought that the polarization corresponding to the highest voltage 

 might not have time to decay before the two condensers were connected 

 together. The wooden arms were flung over the copper plugs by hand, 

 however, so that the time interval of decreasing the potential of one 

 condenser was of the order of 1/20 second. This is probably too long 

 a time for a perceptible lag effect to continue ; the throws obtained 

 were, however, considerable. But the charges behaved in every way 

 just like residual charges, taking an appreciable time to come out 

 of the condenser, although they had been formed in a very short 

 time. 



The principle of the method of mixtures which was here used was 

 carried over into the later work with great advantage. In these new 

 experiments the condenser to be tested was opposed to a standard 

 air condenser, in which no residual charge formation was supposed to 

 occur. Thus comparisons were rendered simple, as no variable effects 

 due to one condenser had to be eliminated 



