388 THIRD REPORT— 18.]^. 



city of a conductor : the extent of edge is merely a function of 

 the pecuhar kind of extension to which the given area has been 

 subjected, and by which the electrical particles become placed 

 in I'espect of each other, in such way as to diminish their ope- 

 ration on external bodies, that is to say, their intensity. 



This view seems confirmed by numerous experiments made 

 by the author. The same plates turned into cylinders, both in 

 the direction of their lengths and breadths, were found to have 

 still the same capacities, that is to say, whether the conductor 

 was simply a plate or an open cylinder. Neither did any differ- 

 ences ai'ise in turning a given plate into other figures approach- 

 ing cylinders, such as triangular and hexagonal prisms. The 

 capacity of a sphere, also, is the same as a plane circular area of 

 equal superficies. Hence the capacity of a cylinder or sphere 

 for free electricity, may be conceived to be the same as that of 

 the plane area into which it may be supposed to be rectified. 



These results seem of some consequence to the theory of 

 electrical action. It has been found, for example, that the in- 

 terior surface of a sphere charged with free electricity does not 

 electrify a conducting substance when placed completely within 

 it ; it has been hence inferred, that the electrical accumulation is 

 disposed altogether upon its exterior surface. Now the inten- 

 sity of a sphere being the same as that of a plane area of equal 

 superficial extent, it should follow that the electrical distribution 

 is in each case the same, since it is difKcult from any known fact 

 to suppose a given quantity of electricity expanded over twice 

 the surface, as in the plane area, and yet maintain the same 

 intensity. The redundant electricity, therefore, if the above 

 deduction be true, sliould only be disposed on one side of the 

 plate. 



Since the capacity of plane conductors varies in an inverse 

 ratio of their area and linear dimensions, it is requisite, if we de- 

 sire to obtain plane surfaces whose capacities for electricity shall 

 be double, treble, &c., of each other, to construct the plates so 

 that their areas and linear dimensions shall be likewise double, 

 treble, &c., of each other respectively. 



The law according to which the force of electrical attraction 

 varies at different distances is an important object of physical 

 research. It may be easily and satisfactorily arrived at by the 

 methods of expei'iment above mentioned. The author exhibited 

 to the Section, by the means of his balance, the resulting law 

 of electrical force -when exerted between two circular plane 

 areas directly opposed to each other, at different distances, and 

 which was found to be in an inverse ratio of the squares of the 

 respective distances exactly. 



