Experiment on the Ley den Jar. with Movable Coatings. 491 



surface is not so hygroscopic as glass. After some trouble I 

 succeeded in casting a thin but perfect jar of paraffin fitting 

 the same metal coatings as a glass jar I had. 



The usual experiment was tried with this, but instead of 

 charging the jar from an electrical machine, the jar was 

 connected to a gold-leaf electroscope* and charged from an 

 electrophone. 



By this method one does not need such high potentials, 

 there is less loss from leakage, and it is possible to see what 

 is going on and make approximate quantitative measurements. 



In this way the jar was charged to 500-600 volts, and the 

 deflexion on the electroscope noted. The inner coating of 

 the jar was then lifted out by an insulating handle, touched 

 to the outer coating and replaced. It was then re-connected 

 to the electroscope. Contrary to the case with the glass jar 

 there was no appreciable charge remaining in the jar ; in fact, 

 repeated experiment showed that on lifting out the inner 

 coating and earthing it, or connecting it to the outer coating, 

 the dielectric was completely discharged in the act, and only 

 the barest trace of charge remained when the inner coating 

 was put back. Also the charge evidently came away on the 

 inner metallic coating when it was lifted out, as could be 

 plainly seen on the electroscope. In fact, the action was 

 exactly the reverse to the account of it usually given. On 

 the other hand, the actions as now found seemed completely 

 in accord with the Faraday-Maxwell theory, and with known 

 electrostatic laws. Briefly they showed, that the action on 

 the dielectric is inductive, that if the inner charged electrode 

 were brought outside, the lines of force going to the outer 

 electrode no longer went through the dielectric, which ac- 

 cordingly lapsed to its normal and neutral state. 



If when the jar with paraffin dielectric is charged it is 

 placed on an insulated stand and both coatings are taken off 

 by insulated handles, both coatings will be found to have 

 strong and equal charges of opposite signs. If these two 

 coatings are then touched together, and the jar is reconsti- 

 tuted, it will be found to have no charge as before. 



Having thus clearly shown that there is a difference in 

 the results of the experiment when glass is used and a better 

 dielectric such as paraffin, I determined to vary the glass 

 experiment as follows : — The glass jar was first thoroughly 

 warmed. It was then put in a largo dry cupboard, and kept 

 dry for a couple of days by means of plenty of calcium 

 chloride. 



This dry cupboard is so arranged that, by means of oil silk 

 sleeves passing through holes in one of the sides, and we 1 ring 



