SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 489 



figures have been given, is about 185 cms. ; this was the highest drop 

 obtainable on the machine. 



The method of procedure was as follows : after a test condenser of 

 capacity very nearly equal to that of the air condenser had been con- 

 nected up as shown in the diagram, while the battery circuit was still 

 open, the iron weight was raised a little above the lead strips, and these 

 were clamped after having been properly adjusted, so that the knife 

 edges should plough furrows of moderate depth on the surfaces of the 

 lead. Then the iron weight was pushed up into its trap (k, Figure 1), 

 and the commutating key v of the condensers, which had thus far kept 

 both condensers short-circuited, was lifted from the mercury wells. 

 The battery circuit was now closed, thus keeping the brass plate of 

 the east knives at high potential, and the iron weight with the north 

 and south knives at low potential. The observer now brought the coil 

 of the d'Arsonval galvanometer g to rest, pulled with the right hand 

 the string which released the iron weight, and at the moment when 

 the iron weight was heard to strike into the dash pot he dropped the 

 commutator key v into its mercury wells in the neutralizing position, 

 connecting the positive terminal of each condenser with the negative 

 plate of the other. The condensers destroyed each others' charges 

 approximately, leaving a remainder which was then sent through the 

 galvanometer by dropping the galvanometer key u into its mercury 

 wells. The ballistic throw was read and recorded, together with the 

 voltage of the battery and the conditions controlling the charging 

 interval. Then, if there were no secondary residual charges, the con- 

 densers were short-circuited by their commutating key, the galva- 

 nometer coil was brought to rest by short-circuiting its terminals, the 

 key of the storage battery was opened so as to protect the battery 

 from a possible short circuit while the lead strips were loosened and 

 drawn aside, and the iron disk in the dash pot was pulled up to its 

 normal position. Then operations were repeated. 



The experiments just described were begun on February 10, and 

 carried on until March 27, 1908. The earlier results were not of the 

 high accuracy which characterizes nearly all the observations taken on 

 and after March 10. It was at one time suspected that the storage 

 battery could not respond fully to demands in the very short charging 

 intervals. But the real cause of occasional disagreements in the ballis- 

 tic throws obtained was later found to lie in imperfect contacts of the 

 storage battery leads on the switch-board. I shall merely summarize 

 below the results obtained in the earlier part of the work on various 

 test condensers, by giving mean values of several observations, and 

 their reduction to the final values of residual charge expressed in per- 



