LAWS OF STATICAL ELECTRICITY BY INDUCTION. 235 



arise when the same transfer-plate is employed for successive transfers of the electri- 

 city, in consequence of again withdrawing a small portion of the charge deposited on 

 the circular plate ; commonly, however, this is of little consequence, the capacity of 

 the large plate being very considerable in respect of the capacity of the smaller one. 

 We may, however, avoid the discrepancies by means of two or three small plates, pre- 

 cisely equal, so as to place each in succession on the larger one. 



(r.) Two plane conductors being alternately connected with the electrometer, whose 

 areas and perimeters were, in one, double of the other respectively, the intensity 

 of a given quantity, when disposed on them, was, according to the general law (16.), 

 in an inverse ratio of the square of the surface. This law, however, did not obtain 

 when the area only was double, without regard to the perimeter. Thus, in two 

 circular plates or parallelograms, in which the area of one plate, was double of the 

 other, the lengths of the latter being in the ratio of 2 : 1, the respective intensities 

 were found to be very nearly in an inverse ratio of the areas ; a somewhat remarkable 

 fact. 



58. We may conclude from these phenomena, that the intensity does not vary in 

 an inverse ratio of the square of the surface, according to the general law (16.), ex- 

 cept when the areas are so disposed ; . that the whole perimeter of the various plates, 

 is as the respective surfaces ; a result which applies also to cylindrical conductors, the 

 electrical capacities of these being the same as the plane areas, into which we may 

 conceive them to be expanded (54.). 



59. The curious fact, that the capacity of a sphere or cylinder is the same as that 

 of the plane area into which it may be supposed to be rectified, seems to afford some 

 new views in electricity. We find in the case of electricity accumulated on a hollow 

 sphere, that a conducting substance, insulated and placed entirely within the sphere, 

 remains in a neutral state ; from which it has been inferred that the charge resides 

 only on the exterior surface. Now the intensity of a sphere being the same as that 

 of a plane circle of equal area, it should follow that the distribution is in each 

 alike, since it is difficult, from any known fact, to suppose a given quantity of electri- 

 city expanded over twice the surface, as may be inferred in the latter case, and yet 

 maintain the same intensity : the redundant electricity, therefore, if the above deduc- 

 tion be true, should be also disposed on one side of the plate only, notwithstanding 

 that it may be determined to either when operated upon by a neutral body. 



60. The great difference in the condition of an electrified sphere and that of a plane 

 of equal area, seems to consist in the diffbrence of the relation of one of the surfaces 

 of the sphere in respect to neutral bodies. It may be observed, in the case of a neutral 

 body becoming electrified from either side of the plane area, that some portion of the 

 body is always elevated without the surrounding plane ; and if a similar condition be 

 fulfilled in respect of the interior surface of a sphere, there will remain no difficulty in 

 obtaining electricity from that surface, and as readily as from the other : thus, a sub- 

 stance insulated within the sphere, at the extremity of a conducting rod, projecting in 



