664 lECTURE LIII. 



account of a change of the disposition of the fluid which it contains, upon 

 the approach of a body either positively or negatively electrified. The elec- 

 trical affection produced in this manner, without any actual transfer of the 

 fluid, is called induced electricity. 



When a body positively electrified approaches to a neutral body, the re- 

 dundancy of the fluid expels a portion of the natural quantity from the near- 

 est parts of the neutral body, so that it is accumulated at the opposite extre- 

 mity; while the matter, which is left deficient, attracts the redundant fluid 

 of the first body, in such a manner as to cause it to be more condensed in the 

 neighbourhood of the second than elsewhere; and hence the fluid of this body 

 is driven still further ofi", and all the cff'ects are redoubled. The attraction of 

 the redundant fluid of the electrified body, for the redundant matter of the neu- 

 tral body, is stronger than its repulsion for the fluid which has been expelled 

 from it, in proportion as the square of the mean distance of the matter is 

 smaller than that of the mean distance of the fluid : so that in all such cases 

 of induced electricity, an attraction is produced between the bodies concerned. 

 And a similar attraction will happen, under contrary circumstances, when a 

 neutral body and a body negatively electrified, approach each other. 



The state of induced electricity may be illustrated by placing a long con- 

 ductor at a little distance from an electrified substance, and directed towards it ; 

 and by suspending pith balls or other light bodies from it, in pairs, at different 

 parts of its length : these will repel each other, from being similarly electrified, at 

 the two ends, which are in contrary states of electricity, while at acertain point 

 towards the middle, they will remain at rest, the conductor being here perfectly 

 neutral. It was from the situation of this point that Lord Stanhope first inferred 

 the true law of the electric attractions and repulsions, although Mr. Cavendish 

 had before suggested the same law as the most probable supposition. 



The attraction, thus exerted by an electrified body upon neutral substances, 

 is strong enough, if they are suflSciently light, to overcome their gravitation, 

 and to draw them up from a table at some little distance: upon touching 

 the electrified body, if it is a conductor, they receive a quantity of electricity 

 from it, and are again repelled, until they are deprived of their electricity by 

 Contact with some other substance, which^ if sufficiently near to the first, is 

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