*l$6 EXPERIMENTS ON ELECTRICITY. 



fooner rofe by doubling to a perceptible quantity, than that 

 electricity which they might have poffefled in thefirft cafe. 

 An infulatcd But to make the experiment in a more direct manner, ufing 



pfawdTncontaa tne d° u bler only as an inftrument of admeafurement, he took 

 with a table, a copper plate thirteen inches in diameter, having its furface 

 proximadng fur. rather convex, furnifhed with aninfulating handle of oiled glafs 

 race became ne- four inches long, and baked till the whole was well hardened, 

 gauve. Q ne en( j Q £ ^jg gl a f s was fixed into a copper focket in the 



middle of the plate, and the other end into wood, that it 

 might not be neceflary to touch the electric part of the handle. 

 This copper plate was placed flat upon a mahogany table, and 

 the doubler being deprived of its electricity, the revolving 

 plate B was placed parallel to A, fo that B was connected 

 with the earth ; then the copper plate was lifted up by its in- 

 fulating handle, and applied to the plate A. And lafily, the 

 plate B being revolved only five times, caufed the gold leaf of 

 the electrometer to diverge negatively to the diftance of a 

 quarter of an inch. 

 The fame refult it might in this in fiance eafily have been ftated, that the 

 of water was contact of the copper plate with the mahogany table, did in 

 ufed inftead of fact produce electricity by excitation or friction. But to ob- 

 viate this, he firft repeated the experiment, by touching the 

 copper plate with the point of a needle, and then applying it 

 to the doubler as before, and he found that the inftrument did 

 not produce its fpontaneous electricity in lefs than 15 revolu- 

 tions ; after which touching the copper plate again with the 

 needle, he applied it to the furface of fome water contained in 

 a large difh, fo that its convex part touched the fluid; and 

 then lifting it up he applied it to the doubler, and electricity 

 was communicated, fufficient to caufe the gold leaf to diverge 

 negatively at five revolutions, as in the former experiment. 

 When the touch The kit. experiment with the water was repeated, with this 

 theoppofite difference only, that the application of the Copper plate was 

 power was ob- made to the revolving plate of the doubler, inftead of the plate 

 A, the revolving plate being moved a little paft its contact 

 with the ball, and the plate A being at that time made to 

 communicate with the earth by the brafs wire j five revolu- 

 tions in this cafe produced electricity as before, but the elec- 

 tricity of the plate A was now pofitive, as might be expected 

 in confequence of the negative charge having been commu- 

 nicated to B intfead of A. 



The 



tained. 



