390 Royal Society: — Mr. J. Thomson on Contact 



plates were lifted as carefully as possible, yet it was not certain 

 that friction had been entirely got rid of, so the following experi- 

 ments were made to show that there is an electrical displacement 

 when two non-conductors or a conductor and a non-conductor are 

 put in contact without friction. 



The arrangement used was as follows : — 



Glass rods, AB, CD, EF, GrH, were fixed in a wooden frame 

 ACGrE ; round these rods silk threads, BE, DH, were wound ; an 

 aluminium needle carrying a mirror, M, was huug by a silk thread 

 from a brass rod, T, fastened in the wooden frame ; a wire from 

 the needle dipped into a glass vessel, N, containing sulphuric acid ; 

 a small magnet was fastened to the back of the mirror, and a glass 

 case was placed over the whole; outside the glass case were mag- 

 nets, by means of which the position of the needle was regu- 

 lated ; a wire also from the outside dipped into the vessel N", 

 and was used to charge the needle with electricity ; positive elec- 

 tricity was got from an ordinary electrophorus, negative from 

 an electrophorus in which the resin was replaced by a plate of 

 glass ; which was excited by silk. If wax and glass were the sub- 

 stances experimented on, a cake, OQEP, was made, one half of 

 which, OSQ, was glass, the other half, IIPS, being wax ; the junction 

 of the wax and glass was parallel to OQ, the wax sticking fast to 

 the glass : this cake was then placed on the silk threads under the 



■I 1 ^ 



n 



B 

 lip 



needle, and it was found possible to bring the needle into such a 

 position that when it was charged with positive electricity it was 



