verified by experiment 



187 



381] 2ndly, I made a plate of a mixture of rosin and bees wax *, about 

 8 inches square and somewhat more than -12 thick, and coated it with 

 circles 6-61 in. diameter. Its charge was found to be to that of the plates 

 K, D and E together as 56 to 55, and therefore should be equal to that of 

 a plate of glass of the same kind as K whose thickness is -345 and the 

 diameter of whose coatings is the same as those of the rosin plate, namely 

 6-61 inches. 



This plate was then inclosed between the glass plates B and //f, the 

 coatings being first taken off, and the outside surfaces of B and H coated 

 with circles 6-6 inches in diameter. Its charge was found to be to that of 

 K as 7-56 to 8. 



According to the foregoing rule, its charge should be the same as that 

 of a plate of glass of the same kind as B -634 of an inch thick with coatings 

 6-6 inches in diameter, and should therefore be to that of K as 7-34 to 8, 

 which is very nearly the same that it was actually found to be. 



382] On the charges of such Leyden vials as do not consist of flat 

 plates of glass. 



These experiments were made with hollow cylindrical pieces of glass, 

 open at both ends, and coated both within and without with pieces of 

 tinfoil surrounding the cylinder in the form of a ring, the breadth of the 

 ring being everywhere the same, and the inside and outside coatings being 

 of the same breadth, and placed exactly opposite to each other. Only as 

 the inside diameter of the two thermometer tubes was too small to admit 

 of being coated in this manner, they were filled with mercury by way of 

 inside coating. 



The thickness of the glass was found by suspending the cylinder by 

 one end from a pair of scales with its axis in a vertical position, and the 

 lower part immersed in a vessel of water, and finding the alteration of 

 the weight of the cylinder according as a greater or less portion of it was 

 under water J. 



383] The result of the experiments is contained in the following table . 



[Arts. 548, 6 7 8.J 

 [Art. 594.] 



t [Arts. 552, 679.] 



[See Art. 676, and Note 28.] 



