268 journal of Experiments, March ', 1773 



The electricity was found to break through the rosin plate when electrified 

 with this strength, but there was no hole made in the plate, as it was found not 

 to break through after that with the weak degree of electrification. It seemed 

 not to pass over the surface, as no light was perceived. 



552] Charge of compound plate of glass and rosin. 



The rosin plate of p. 79 [Art. 548] without its coatings was included between 

 the plates B and H of Nairne and the outside surfaces coated with circles 

 6-6 inc. diam. and is called Compound Plate. 



Th. Mar. n [1773]. Th. 53. N. 17. [4 comparisons with K.] 



Fr. Mar. 12 [1773]. Th. 53^. N. 13$. [20 observations, Art. 664.] 



553] Circle of i8" compared with double plates, also plate D, plate air and 

 the two double plates compared with circles of 36" and 30". 



A sliding trial plate was made of deal, with an additional piece to fit on, 

 the breadth was 31 inches, the length when not drawn out, and without the 

 additional piece, was 15, and the additional piece increased the length rof inches. 



The number in the 2 nd column shews the number of inches by which the 

 sliding piece is drawn out. 



Tu. Mar. 9. [Electrometer] At inner marks. At outer marks. 



Difif. Mean Diff. Mean 



Circle 36" n-6 35-6 5-8 36-3 



E 12-2 32-5 6-9 33-2 



Circle 30" 11-4 30-4 7 30-8 



March 12. [14 observations.] 



Sat. Mar. 13. Th. 55. N. 12. [12 observations. See Art. 649.] 



Mon. Mar. 15. Th. 54. N. 14. [15 observations. See Arts. 649, 655.] 



554] The same with addit. four small rosin plates. 



Four plates of rosin and bees wax were cast 4 inches square and about 

 22 thick and coated with circles 1-8 in. diam. A tin trial plate was also made 

 6 inches long and 5 broad. It is called N. The plates of rosin were connected 

 by bits of brass wire like that used for connecting the two double plates. 



