12 



ELECTRICITY. 



and charged with any one species of 

 electricity, for other bodies similarly 

 charged, is derived from the repulsive 

 power which the particles of this fluid 

 exert towards those of their own species. 

 Let us suppose a body charged with 

 electricity to be suspended in the air, or 

 otherwise surrounded by a non-con- 

 ducting medium, which allows it to 

 move freely. As long as this body re- 

 mains alone, the outward pressure 

 which the electric fluid exerts against 

 the insulating medium that confines it, 

 will, by the laws of hydrostatics, be 

 equal on all sides ; and the body, thus 

 balanced by equal and opposite pres- 

 sures, will nave no tendency to move. 

 But if another body, similarly circum- 

 stanced, be brought near it, the repul- 

 sive action between the similar electri- 

 cities contained in these bodies, will 

 diminish the outward pressures of each 

 fluid against the sides of the bodies, 

 (6, c,fig. 8.) which are adjacent to each 



other ; and it will, at the same time, 

 increase the outward pressure on the 

 opposite or remoter sides (a, d.) Both 

 these causes conspire to destroy the 

 equilibrium ; each body is impelled in 

 the direction of the preponderating 

 force, that is, in a direction from the 

 other body ; and an effect, which may 

 be called repulsion, takes place. The 

 very same explanation, it is evident, 

 applies to both kinds of electricity, their 

 properties being in this respect exactly 

 alike. 



If, on the other hand, a body charged 

 with vitreous electricity be presented to 

 one that is charged with resinous electri- 

 city, the attraction of these two fluids will 

 diminish the outward pressure on the 

 remote sides oi the bodies, and increase 

 it on the adjacent sides ; hence, the 

 bodies will be urged towards each other, 

 and motions indicative of attraction will 

 result. Thus, in all cases, do the move- 

 ments of the bodies represent the forces 

 themselves which actuate the particles 

 of the developed electricities they con- 

 tain. 



(47.) Induction. The law of induc- 

 tion is a direct consequence of the hypo- 

 thesis we are considering. Wherever 

 pne of the electricities exists in an active 



state, it must repel the particles of the 

 same electricity in all surrounding bo- 

 dies, and attract those of the opposite 

 species : or, in other words, it tends to 

 decompose their united electricities, ac- 

 cumulating the electricity of the oppo- 

 site species towards the nearest side, 

 and impelling that of the same species 

 towards the remote side. The body 

 thus acted upon is no longer neutral, 

 although it contains, on the whole, its 

 natural quantities of both electricities ; 

 but, in consequence of their partial dis- 

 tribution, electrical appearances will be 

 exhibited in its different parts. The 

 further prosecution of this branch of 

 the subject must also be postponed to a 

 subsequent chapter, our present object 

 being merely to point out, in a general 

 way, the coincidence of the fundamental 

 facts with the proposed theory. 



(48.) Thus far we have proceeded 

 upon the hypothesis of there being two 

 distinct electric fluids, having certain 

 properties in common, but each being 

 characterized by a certain modification 

 of these properties. It is, however, 

 equally possible to account for ah 1 the 

 phenomena with the same exactness, on 

 the supposition of their resulting from 

 the agency of a single electric fluid. 

 This simplification of the theory may be 

 considered as the discovery of the im- 

 mortal Franklin, although it had oc- 

 curred at the same period to Dr. Wat- 

 son ; for it was Franklin who first 

 pointed out the mode in which it might 

 be successfully applied to explain some 

 of the most remarkable phenomena of 

 the science. Several particular points 

 in his theory, as he originally proposed 

 it, were defective, and were found on 

 strict examination to be at variance with 

 ascertained facts. It is to ^Epinus and 

 to Cavendish that we owe the rectifica- 

 tion of these errors : and the theory of 

 Franklin, as thus amended, whatever 

 alterations the future progress of disco- 

 very may oblige us to make in it, will 

 ever remain one of the most beautiful 

 specimens of this kind of reasoning 

 which philosophy has produced. Of 

 this hypothesis we shall now present a 

 brief outline ; and point out the mode 

 in which it explains the phenomena. 



(49.) We set out, then, with sup- 

 posing that there exists in all bodies a 

 subtile fluid, which we shall call the 

 electric fluid ; that its particles repel 

 one another with a force varying in- 

 versely as the square of the distance ; 

 that they attract the particles of all 



