266 "Journal of Experiments, March, 1773 



Wed. March 3 [1773]. Th. 56. N. 21. [16 observations.] 



548] Charge of plate of experimental rosin designed for compound plate of 

 glass and rosin; tried both when warm and when cold *. 



A plate of experimental rosin near 8 inches square was pressed out between 

 two glass plates with tinfoil coatings fastened on by oil, the heat being such 

 that it required very little weight to press out the 5 rosin. 



The thickness of the plate was much less toward one end than the other, 

 varying in different parts of the coated plate from -137 to -108, but the mean 

 thickness was -122. 



It was coated with circles of tinfoil 6-61 in. diameter. 



Its charge was compared with that of the plates K, D and E of Nairne by 

 means of a sliding trial plate made of the plate f of Nairne. 



Sat. March 6 [1773]. Th. 55$. N. 17. 



Tr. si. pi. 



K + D + E 



ros. plate 



In the afternoon. Th. 57^. N. 16 

 ros. plate 



K4- D+ E 



24 

 19 



25 

 19 



sep. neg. 

 D pos. 



D neg. 



sep. pos. 

 D neg. 

 D". 



The rosin plate was then warmed before the fire between two glass plates 

 with flannel between them and the rosin till it would not support its own 

 weight without bending. As soon as it was strong enough to bear its own 

 weight it was compared as before. 



rosin plate 



sep. pos. 

 did not sep. 

 In about 2 or 3 hours after, when it was quite cold, it was tried again : 



2o 

 26 



rosin 25 sep. pos. 



19 D pos. 



i8J DO. 

 24^ D neg. 

 549] Whether charge of glass plate is the same when warm as when cold. 



The same afternoon the charge of a glass plate when hot and cold was 

 compared together in the same manner. 



The glass was nj inches square, used for jEpinus experiment {, coated on 

 one side with a circle of 8 inc. diameter, and a brass plate of same diameter 

 used for the other coating. 



The glass and brass plate were both heated before the fire till almost as hot 

 as I could bear my hand on, and then tried by the help of the 6 th sliding plate, 



* [Arts. 381, 678.] t [So in MS.] } [Arts. 134, 341, 517.] 



