ELECTRICITY IN EQUILIBRIUM. SI 



surface, indicating also in some cases the species of electricity, 

 whether positive or negative, that has been employed ; positive 

 electricity producing an appearance somewhat resembling feathers; 

 and negative electricity an arrangement more like spots. The 

 inequality in the distribution of the electric fluid in a nonconduc- 

 tor, may remain for some hours, or even some days, continually 

 diminishing till it becomes imperceptible. 



These are the fundamental properties of the electric fluid, and 

 of the different kinds of matter as connected with that fluid. We 

 are next to examine its distribution, and the attractive and repul- 

 sive effects exhibited by it, under different forms. Supposing a 

 quantity ef redundant fluid to exist in a spherical conducting body, 

 it will be almost wholly collected into a minute space contiguous 

 to the surface, while the internal parts remain but little over- 

 charged. For we may neglect the actions of the portion of fluid 

 which is only occupied in saturating the matter, and also the effect 

 of the matter thus neutralised, since the redundant fluid is repelled 

 as much by the one, as it is attracted by the other; and we need 

 only to consider the mutual actions of the particles of this super- 

 fluous fluid on each other. It may then be shewn, in the same 

 manner as it is demonstrated of the force of gravitation, that all 

 the spherical strata which are remoter from the centre than any 

 given particle, will have the whole of their action on it annihilated 

 by the balance of their forces, and that the effective repulsion of 

 the interior strata will be the same, as if they were all collected in 

 the centre. This repulsion will, therefore, impel the particles of 

 the fluid towards the surface, as long as it exists ; and nothing will 

 impede the condensation of the redundant fluid there, until it is 

 exhausted from the neighbourhood of the centre. In the same 

 manner it may be shewn, that if there be a deficiency of fluid, it 

 will be only in the external parts, the central parts remaining 

 always in a state of neutrality : and since the quantity of electric 

 fluid taken away from a body, in any common experiment, bears 

 but a very small proportion to the whole that it contains, the defi- 

 ciency M ill also be found in a very small proportion of the sphere, 

 next to its surface. And if, instead of being spherical, the body 

 be of any other form, the effects of electricity will still be princi- 

 pally confined to its surface. This proposition wag very satisfac- 

 torily investigated by Mr. Cavendish ; and it was a'terwarcls more 

 fully shewn, by Dr. Gray's experiments, that the capacities of 



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