374 On the Laws and Operation of Electrical Force. [June 16, 



to be in an inverse ratio of tlie exposed surfaces, as in the former expe - 

 riments. 



Experiment 16. Comparison of a sphere of 7 inches diameter with a 

 circular plate of 14 inches, or double that diameter. In this case the 

 inner and outer surface of the sphere, taken together, are actually the 

 same as the two surfaces of the plate. The inner surface of the sphere 

 being closed, however, as in the last experiment, the surfaces of the sphere 

 and plate, electrically considered, are therefore not equal, and the surface 

 of the plate is twice the surface of the sphere. The surfaces, therefore, 

 open to external induction are as 2 : 1 . 



On examining the charges of the plate and sphere, they were found to 

 be as 10: 14, or as 1 : 1*4 ; charge of sphere being 10 circular inches, 

 under an intensity of 20°, and charge of plate being 14 circular inches, 

 imder the same intensity of 20°. The charge of the sphere, therefore, as 

 compared with the charge of the plate, is as 1 : V 2, that is, as the square 

 roots of the exposed surfaces. 



On examining the intensities of the sphere and plate, they were found to 

 be, as in the preceding experiments, in an inverse ratio of the exposed sur- 

 faces. We cannot, therefore, conclude, as already observed (4), that the 

 capacity of the plate is twice that of the sphere. 



19. The following experiments are further adduced in support of the 

 preceding : — 



Experiment 17. A copper plate 10 inches square, compared with the 

 same plate rolled up into an open hollow cylinder, 10 inches long by 3*2 

 inches diameter. Here, as in the last experiments, although the surfaces 

 are actually the same, yet, electrically considered, the plate has twice the 

 surface of the cylinder, one surface of the cylinder being shut up. 



On examining the charges of the cylinder and plate, they were found to 

 be, as in the preceding experiments, as 1 : V 2 ; that is, as the square roots 

 of the exposed surfaces, and the intensities in an inverse ratio of the sur- 

 faces, which seems to be a general law for closed and open surfaces. 



Experiment 18. A hollow copper cube, side 5*7 inches, surface 195, 

 compared with a hollow copper sphere of diameter equal side of cube, 

 surface 103 square inches nearly. 



On examining the charges of the sphere and cube, they were found to 

 be as 9 : 1 nearly ; charge of the sphere being 9 circular inches, under an 

 intensity of 10°, and charge of cube being 10 circular inches, under the 

 same intensity of 10°. The charges of a cube, and of a sphere whose dia- 

 meter equals the side of the cube, approach each other, notwithstanding 

 the differences of the surfaces, owing to the six surfaces of the cube not 

 being in a disjointed or separated state. 



20. The author observes, in conclusion, that the numerical results of the 

 foregoing experiments, although not in every instance mathematically exact, 

 yet upon the whole were so nearly accordant as to leave no doubt as to the 

 law in operation. It would be in fact, he observes, assuming too much to 



