1864.] 



of Electrical Force. 



371 



suspended neutral disk of the electrometer, or from the increased surface 

 attendant on the connexion of the surface under experiment with the fixed 

 plate of the electrometer ; as also, that it is of no consequence whether the 

 suspended disk be placed immediately over the fixed attracting plate of the 

 electrometer, or over any point of the attracting surface in connexion 

 with it. 



1 7. Having duly considered these preliminary investigations, the author 

 now proceeds to examine experimentally the laws of surface and boundary 

 as regards plane rectangular surfaces, and to verify the formulae C=^S.B, 



and E=-i-; in which C=charge, E=intensity, S = surface, and B = 



boundary. 



For this purpose a series of smoothly-polished plates of copper were em- 

 ployed, varying from 10 inches square to 40 inches long by 2*5 to 6 inches 

 wide, and about ^th of an inch thick, exposing from 100 to 200 square 

 inches of surface. 



The charges (1) of these plates were carefully determined under a given 

 electrometer indication, the attracting plates being at a constant distance. 



Experiment 7. In this experiment, a copper plate 10 inches square is 

 compared with a rectangular plate 40 inches long by 2*5 inches wide. 



In these plates the surfaces are each 100 square inches, whilst the boun- 

 daries are 40 and 85 inches. The boundaries may be taken, without sen- 

 sible error, as 1 : 2, whilst the surfaces are the same. 



On examining the charges of these plates, charge of the square plate 

 was found to be 7circular inches, under an intensity of 10'^. Charge of the 

 rectangular plate 10 circular inches nearly, under the same intensity of 10°. 

 The charges therefore were as 7 : 10 nearly, that is, as 1 : 1*4 nearly ; being 

 the square roots of the boundaries, that is, as 1 : V2. 



Experiment 8. A rectangular plate 37'5 inches long by 2*7 inches wide, 

 surface 101 square inches, boundary 80*5 inches, compared with a rect- 

 angular plate 34*25 inches long by 6 inches wide, surface 205 square 

 inches, boundary 80*5 inches. 



Here the boundaries are the same, whilst the surfaces may be taken as 

 1 : 2. 



On determining the charges of these plates, charge of the rectangular 

 plate, surface 101 square inches was found to be 8*5 circular inches under 

 an intensity of 8°. Charge of the plate with double surface =205 square 

 inches, was found to be 12 circular inches under the same intensity of 8° ; 

 that is to say, whilst the surfaces are as 1 : 2, the charges are as 8*5 : 12 

 nearly, or as the square roots of the surfaces, that is, as 1 : -v/ 2. 



Experiment 9. A rectangular plate 26*25 inches long by 4 inches wide, 

 surface 105 square inches, boundary 60*5, compared with a rectangular 

 plate 40 inches long by 5 inches wide, surface 200 square inches, boundary 

 90 inches. 



Here the surfaces are as 1 : 2 nearly, whilst their boundaries are as 2 : 3. 



VOL. XIII, 2 E 



