508 LECTURE LIII. 



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

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

 tion 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 elec- 

 tricity, and to examine the natural and artificial apparatus concerned in 

 electrical phenomena, as well as in those effects, which have been denomi- 

 nated galvanic. 



It is supposed that a peculiar ethereal fluid pervades the pores, if not 

 the actual substance, of the earth and of all other material bodies, passing 

 through them with more or less facility, according 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 distances 

 of the particles. 



The effects of this fluid are distinguished from those of all other sub- 

 stances by an attractive or repulsive quality, which it appears to commu- 

 nicate to different bodies, and which differs in 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. 



These repulsions and attractions are supposed to act, not only between 

 two particles which are either perfectly or very nearly in contact with 

 each other, but also between all other particles at all distances, whatever 

 obstacles may be interposed between them. Thus, if two electrified balls 

 repel each other, the effect is not impeded by the interposition of a plate of 

 glass : and if any other substance interposed appears to interfere with their 

 mutual action, it is in consequence of its own electrical affections. In 

 these respects, as well as in the law of their variation, the electrical forces 

 differ from the common repulsion which operates between the particles of 

 elastic fluids, and resemble more nearly that of gravitation. Their 

 intensity, when separately considered, is much greater than that of 

 gravitation, and they might be supposed to be materially concerned in the 

 great phenomena of the universe ; but in the common neutral state of all 

 bodies, the electrical fluid, which is every where present, is so distributed, 

 that the various forces hold each other exactly in equilibrium, and the 

 separate results are destroyed ; unless we choose to consider gravitation 

 itself as arising from a comparatively slight inequality between the elec- 

 trical attractions and repulsions. 



The attraction of the electric fluid to common matter is shown by its 

 communication from one body to another, which is less copiously supplied 



