SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 487 



Table V gives the detail of the observations taken under these 

 conditions. 



The next to the last observation of Table V was taken under the 

 same conditions as for a time of 0.0032 seconds, save that the weight 

 was given an acceleration by hand. This shortened both the times of 

 charging voltage and short circuit in much the same proportion, but 

 the larger throw indicates that the change of time of short circuit was 

 of greater influence. For the starred observations, the short circuits 

 were longer than for the others. 



The residual charges in " Par. B " and " Par. C " of Tables VII and 

 VIII had to be short-circuited several times through the galvanometer, 

 since the first discharge did not take away all of the residual formed. 



Table X contains a summary of mean results. 



Experiments with the Falling Weight Machine, using the " Test 

 Condenser versus Air Condenser" Method. 



I now decided to make observations on the actual quantities of resid- 

 ual charge formed in various short charging intervals by using the air 

 condenser to neutralize approximately the whole of the "free charge" 

 of the test condenser, and then measuring the remainder ballistically. 

 The method used from now on till the end of the work was quite simi- 

 lar to the former one in which the knife switches were used and the 

 relay lever changed circuits so that the charge of the air condenser 

 neutralized nearly all the charge of the test condenser. But the relay 

 was now discarded, since its use made the time of charging impossible 

 to control when very short, and it was found best to let the falling 

 weight machine do the charging merely, while the neutralization of the 

 charges was effected by lowering a commutating key by hand immedi- 

 ately after. Then after a short pause, which varied according to the 

 quickness with which the residual charge reappeared, the remaining 

 charge was sent through the galvanometer by lowering another com- 

 mutating key. 



The arrangement of the apparatus and connections is shown in the 

 accompanying diagram (Figure 4). One of the north knives is no 

 longer necessary. The chief points of difference from the short-circuit- 

 ing method of experimenting are: («) the addition of the air condenser a, 

 and (b) the slight raising of the block on which the south lead strip 

 holders s are mounted as indicated in the relative positions at k. The 

 new arrangement changes the former short-circuiting action over into 

 a charging action. The air condenser was as a rule uniformly charged 

 by means of a knife edge cutting the edge of a lead strip clamped 



