18 ELECTRICITY IN EQUILIBRIUM. 



been gradually formed into a theory, by the investigations of 

 Acpinus and Mr. Cavendish, combined with the experiments and 

 inferences of Lord Stanhope, Coulomb, and Robinson. 



\\ c shall first consider the fundamental hypotheses on which 

 this system depends; and secondly, the conditions of equilibrium 

 of the substances concerned in it; determining the mode of dis. 

 tribution of the electric fluid, and the forces or pressures derired* 

 from its action when at rest; all which will be found to be deduc. 

 ed from the theory, precisely as they are experimentally observ. 

 able. The motions of the electric fluid will next be noticed, as 

 far as we can form any general conclusions respecting them ; and 

 the manner in which the equilibrium of electricity is disturbed, or 

 the excitation of electricity, will also be considered ; and, in the 

 last place, it will be necessary to take a view of the mechanism, 

 or the practical part of electricity, and to examine the natural and 

 artificial apparatus concerned in electrical phenomena, as well as 

 in those effects which have been denominated galvanic. 



It is supposed that a peculiar ethereal fluid pervades the pores, 

 if not the actual substance, of the earth, and all other material 

 bodies ; passing through them with more or less facility, accordiiii 

 to their different powers of conducting it : that the particles of 

 this fluid repel each other, and are attracted by the particles of 

 common matter : that the particles of common matter also repel 

 each other : and that these attractions and repulsions are equal 

 among themselves, and vary inversely as the squares of the dis. 

 tances of the particles. 



The effects of this fluid are distinguished from those of all otliei 

 substances, by an attractive or repulsive quality, which it appears 

 to communicate to different bodies, and which differs iu general 

 from other attractions and repulsions, by its immediate diminution 

 or cessation, when the bodies, acting on each other, come into 

 contact, or when they are touched by other bodies. The name 

 electricity is derived from electrum, amber ; for it was long ago 

 observed that amber, when rubbed, continues for some time to 

 attract small bodies ; but at present electricity is usually excited 

 by other means. In general a body is said to be electrified, when 

 it contains, either as a whole, or in any of its parts, more or less 

 of the electric fluid than is natural to it ; and it is supposed that 

 what is called positive electricity depends on a redundancy, and 

 negative electricity on a deficiency, of the fluid, 



