250 "Journal of Experiments^ Dec. 25, 1772 



515] I 9t and 2 nd sliding plates compared with double plate B, also P, Q and O 

 and thin rosin. Old G and whitish plate compared with D, E, F, and M. 



The i sl and 2 nd sliding coated plates were compared with double plate B 

 [6 observations]. The 25 divisions] on slfiding] pl[ate] were measured by using 

 brass plate 3 inc. by ij and 9 div. of the tinfoil. 



2 trial plates were made for plates M &c. out of a white glass hemisphere 

 [8 observations. Art. 656]. 



Fr. Dec. 25 [1772]. Th. 49. N. 20. 



[19 observations, and 3 on insulation. Art. 656.] 



By this exper. with \ ,. trial plate contains < inc. el. less than 

 Ismail I -7 



D, E & F, P 7 ' 3 less, O 4 ' 4 less, old G 2 ' 9 less, whitish plate 4 ' 4 less, and thin 

 "7 7'3 7'3 9'5 



rosin less. 

 17-2 



By mean P contains 9-5 less, 5-8 less, old G 5-1 less, whitish plate 7 less, 

 thin rosin 16 less, and Q -3 less. 



The wires used in the machine were all cleaned between this experiment 

 and the next. 



516] Whether the charge of plate air is diminished by changing the air between 

 them by lifting up the upper plate*. 



In order to try whether in electrifying plate air the electricity was lodged 

 in the air or in the plates, the two brass 8-inch plates were placed on each other 

 with supports of sealing wax to keep them at about -4 inc. distance from each 

 other and placed on the machine f with the end M of the wire Mm resting on it ; 

 the uppermost plate being fastened by a stick of waxed glass and 3 pieces of 

 silk to the end of a lever so that it could be lifted up and down. It was also 

 contrived so that in lifting up the plate the wire Mm was first lifted up from 

 it about J inch, for fear that if Mm rested on the plate when lifted from the 

 under one, some electricity might escape from the ends of the wire Bb, &c. 

 The third sliding trial plate was put on the negative side. 



If the wire Cc was let down and up immediately without lifting up the 

 upper plate, the pith balls separated negatively very little with 18 divisions 

 of sliding plate. 



If the wire Cc was let down and immediately drawn up halfway, but not 

 drawn quite up till the upper plate had been drawn up and let down again, the 

 balls separated very little more. 



The event was the same also if the trial plate was drawn out so that the 

 balls should separate a little positively. 



The upper plate was lifted up 2 or 3 inches. The sliding plate was let out 

 to 12 divisions that the balls should separate positively. 



* [See Arts. 344, 511.] f [Art. 295.] 



