SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 475 



The Condensers used in the Tests. 



Of the many condensers used in the work here described, some were 

 built up of tinfoil and sheets of the best linen ledger paper saturated 

 with paraffin wax of high grade. These were about twelve centimeters 

 long and six and a half centimeters wide. After the paper had been 

 soaked in the wax, the paper and tinfoil were built up into a pile 

 and ironed together with a small flatiron moderately hot ; the pile was 

 then clamped permanently in large malleable iron holders made for the 

 purpose. In the cases of two condensers, known as " Par. KA " and 

 "Par. KB," the flatiron was not used. In "Par. B" and "Par. C" 

 the paper was saturated with paraffin at a temperature near that of 

 boiling water. In " Par. A," " Par. AA," " Par. BB," and " Par. CC " 

 the paraffin was very hot, and the paper was kept in it until all the air 

 bubbles in the paper had apparently been expelled. " Mica A " and 

 " Mica B " were built up at room temperatures of tinfoil and single 

 sheets of mica : after these condensers had been baked and waxed 

 over to keep moisture out they were known as " Mica A " and " Mica 

 B." Besides these a glass condenser, and three to be described later 

 on in which the dielectric was clean, thin paraffin sheets were used. 



Early Experiments with the Falling Weight Machine. 



In these experiments, as has been said above, the falling weight first 

 closed a switch which caused the two condensers to be charged to the 

 same potential of 64 volts, then the relay broke the charging circuits 

 and discharged the condensers against each other, and finally the last 

 switch discharged the compound condenser through a galvanometer of 

 such sensitiveness that the air condenser charged to 1 volt caused a 

 throw of 0.732 centimeters. The sliding weight always dropped 

 through a distance of 57.7 centimeters before it closed the first key, 

 and a total distance of 130 centimeters before it closed the last key. 

 The relay key could be set at any convenient height on its column, 

 but if raised too high there would be no charging of the condensers. 

 Experiment of this kind showed that there was a time lag of 0.0212 

 seconds in the relay circuit, and this had to be allowed for in all the 

 computation. The voltage of the battery was determined by a Weston 

 voltmeter. 



When the relay key was placed as high as it could be without pre- 

 venting the charging of the condensers, the fall of the weight caused a 

 small throw of the galvanometer coil. This throw was due, just as it 

 would be even if the time interval of charging were longer, to two factors : 



