170 



Mr. J. Tliomson on Contact 



[June 15, 



to OQ, the wax sticking fast to the glass : this cake was then placed on 

 the silk threads under the needle, and it was found possible to bring the 



needle into such a position that when it was charged with positive elec- 

 tricity it was deflected from the glass part of the cake, when charged with 

 negative it was attracted towards it. In order to get rid of any electricity 

 which might have got on the cake in the making, the cake was made the 

 day before it was placed on the threads, and the experiment was made at 

 least a day, sometimes a week, after putting the cake on the threads ; 

 pieces of glass and sulphur which had been treated in as nearly as possible 

 the same way as those of which the cakes were made were tak^u and 

 placed separatelj'' on the threads, but no electricity could be detected on 

 them. 



The following cakes were tried : — 



Grlass and wax glass + , wax— ; 



Grlass and resin glass + , resin— ; 



Glass and sulphur glass + , sulphur- 



Glass and solid paraffin . . glass + , paraffin - 



Zinc and sulphur zinc +, sulphur - 



Sulphur and vulcanite .... vulcanite + , sulphur — ; 



the series so far being in the same order as the frictional series : this 

 seems to suggest that the electrical displacement which takes place when 

 two non-conductors are put in contact acts as a predisposing cause, in. 



