-1859] WRITINGS OF JOSEPH HENRY. 327 



the slightest divergence will be seen in the gold leaves, when 

 the globe outside is intensely charged with electricity. The 

 same result will be obtained when a slip of gold leaf is sus- 

 pended in the interior and electrified, either positively or 

 negatively. It does not follow from these experiments that 

 the electricity on the outside does not act on that of the in- 

 side. On the contrary, we must infer from the theory that 

 every atom of electricity at the surface acts repulsively on 

 every atom of electricity in the gold leaf ; but these actions 

 are equal in all directions, and therefore neutralize each 

 other. 



The second proposition may be demonstrated by means 

 of a charged ball and the hollow globe, Fig. 3. If the 

 charged ball, suspended by a silk thread, be placed at about 

 eighteen inches above a gold leaf electroscope, and the diverg- 

 ence noted, and if then the ball be removed and its place 

 occupied by the centre of the globe to which the electricity of 

 the ball has been imparted, the divergence will be the same 

 as before ; or in other words, the action on the electroscope 

 will be the same when a given quantity of electricity is con- 

 centrated on a ball at the centre of a sphere, or diffused 

 throughout the surface of the same body. This experiment 

 may be varied, with more striking results, by placing the 

 hollow globe at a given distance from the electroscope, and 

 then letting down a charged ball into its interior until it 

 reaches the centre: the leaves will be seen to diverge to a defi- 

 nite degree; if the ball be now made to strike the interior sur- 

 face of the globe, by moving the suspending thread of silk» 

 the whole of the charge will pass to the surface of the latter, 

 but the leaves will exhibit the same amount of divergence as 

 before the transfer. The electricity which is distributed 

 throughout the surface of the globe produces precisely the 

 same eflfect as it did when confined to the ball at the centre. 

 The mathematical problem to be solved, for the purpose 

 of calculating the distribution of a given charge of elec- 

 tricit}'- in a body of any form, is to proportion the amount of 

 the fluid in each part of the surface, so that the resultant 

 action on the interior of a body will be completely neutra- 

 lized. This problem, which is simple for the sphere, becomes 



