72 Royal Society : — 



2*5 to 6 inches wide, and about gth 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 

 boundaries are 40 and 85 inches. The boundaries may be taken, 

 without sensible 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 7 circular 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 : V 2. 



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 rectangular 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 rectan- 

 gular 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 : \/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. 



Charge of the rectangular plate surface =105 square inches, 7 

 circular inches under an intensity of 10°. Charge of rectangular plate 

 surface 200 square inches, 12 circular inches, under the same inten- 

 sity of 10°. The charges therefore are as 7:12 nearly, or as 

 1 : \'7i being as the square roots of the surfaces multiplied into 

 the square roots of the boundaries very nearly. 



Experiment 10. A square plate 10 inches square, surface 100 

 square inches, boundary 40 inches, compared with a rectangular 

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

 boundary 90 inches. 



Here the surfaces are double of each other, and the boundaries 

 also double each other, or so nearly as to admit of their being 

 considered double of each other. Charge of square plate 6 circular 

 inches, under an intensity of 10°. Charge of rectangular plate 12 

 circular inches, under the same intensity of 10°. The charges, 



