SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 481 



This tests the principle of superposition by the constancy of the 

 percentage of residual for a given charging interval. The air con- 

 denser gave at first a ballistic throw of 0.732 cms. per volt; after 

 the line of dots an accident changed this to 0.580 cms. per volt ; this 

 sensitiveness was kept nearly constant thereafter. The air condenser 

 has a larger capacity than the paraffin condenser. This explains the 

 change of sign, with increasing time of charging in the ballistic throws. 

 To get true percentages of residual formed in any interval we may, 

 in this case, subtract the percentage values for the longer time from 

 those of the shorter. 



The principle of superposition may be here tested again, if we see 

 whether the percentage values of residual throw are constant for every 

 different charging interval. This condition is seen to be fairly well 

 satisfied, perhaps as well as experimental errors allow, though, in the 

 last block of observations there is a continual numerical decrease in 

 the numbers as we go from lower to higher voltages. The conditions 

 here were, however, somewhat different from those in the other cases. 

 The condensers were charged for a minute, then discharged against 

 each other and left in that connection 15 seconds, then discharged 

 through the galvanometer. 



Experiments with the Falling Weight Machine on the 

 Residual Charges after Short-Circuiting. 



As we see from the results obtained for residual charges formed in 

 different charging intervals, as exhibited in the broken curves of Fig- 

 ure 2 which indicate the mean relative values of the residual-forming 

 current during various increments of the charging time, this current is 

 very much greater during the earlier than during the later stages of 

 the charging. To investigate this matter for much shorter charging 

 times the sliding weight armed with the six knife points in the manner 

 described above was used. The first experiments were made after the 

 manner shown in Figure 3, but without the use of the air condenser. 

 The lead strips are shown below the diagram at k in the relative posi- 

 tions as seen by an observer in front of the machine, it being here 

 assumed that the knife edges are all on the same horizontal level. 

 It will be seen that the charging takes place through one of the 

 right-hand or north knives, and through one of the east knives during 

 the time necessary for the latter to plough across the surface of its 

 lead strip. 



The residual-forming current flows into the dielectric not only for 

 this length of time, but also for the time necessary for the south knife 



VOL. XLIV. — 31 



