ELECTRICITY. 



theory of the double electricities to ex- 

 plain the same phenomena. 



(110.) Another consequence of the 

 induction of electricity must not be over- 

 looked,, namely, that the bodies between 

 which it takes place, necessarily attract 

 one another : for the action of the adja- 

 cent sides F and N ( fig, 25), which are 

 brought into opposite electrical states, 

 is greater than the action of those sides 

 which are in the same electrical states, 

 F and P, and which are more distant : 

 hence the attractive force always exceeds 

 the repulsive. We have already seen 

 that this circumstance sufficiently ex- 

 plains the fact that conducting bodies, 

 previously neutral, are attracted by 

 electrified bodies. Another fact, which 

 appears more singular, and which can- 

 not be accounted for on any other prin- 

 ciple, is also a direct consequence of 

 the law of induction. If a small body 

 weakly electrified, be placed at a dis- 

 tance from another and a larger body, 

 more highly charged with the same 

 species of electricity, it will, as usual, 

 be repelled ; but there is a certain 

 distance within which if it be brought, 

 attraction will take place, instead of re- 

 pulsion. This happens in consequence 

 of the inductive influence producing so 

 great a change in the distribution of 

 electricity, as to give a preponderance 

 to the attractive forces of the adjacent 

 parts of the two bodies, over the repul- 

 sive forces that take place in the other 

 parts, and which would have alone 

 acted if the fluid had been immoveable. 



(111.) From the principles now laid 

 down, it will be easy to understand how 

 induction may operate through a suc- 

 cession of conductors, which are all of 

 them insulated, except the last ; and 

 which are separated from each other by 

 distances greater than that at which a 

 transfer of electricity would take place. 

 If, under such circumstances, the first be 

 electrified, alternate states of opposite 

 electricities will be produced in the two 

 ends of each conductor in succession. 

 In all the ends nearest to the first body, 

 the electricity will be of the opposite 

 kind to that with which the first has 

 been charged ; in the other ends it will 

 be of the same kind as that of the first 

 body. The vicinity of these opposite 

 electricities will tend powerfully to re- 

 tain them in that condition, and will 

 diminish their electric action on sur- 

 rounding bodies. A large portion of 

 the electricities so arranged and re- 

 tained, is, therefore, in the condition 



designated by the term disguised elec- 

 tricity. 



(112.) In proportion as the interrup- 

 tions to the continuity of the line of 

 conductors are more numerous, the 

 more nearly will such a system ap- 

 proach to the condition of an imper- 

 fectly conducting body. The same prin- 

 ciple admits of being extended, with 

 some modifications indeed, to the con- 

 stitution of electrics themselves, as we 

 shah 1 have occasion to notice in the 

 sequel. 



CHAPTERVIII. 



Accumulation of Electricity by 

 Induction. 



(113.) THE most important application 

 of the principle of induction is that by 

 which a vast accumulation of electricity 

 is obtained in a small space, while its 

 intensity, or tendency to escape, is at 

 the same time rendered exceedingly 

 small. This condition exactly corre- 

 sponds to that which has been termed 

 disguised electmcity. 



(114.) Let two circular metallic plates 

 P and N (fig. 28), be placed the one 

 immediately over the other, but sepa- 

 rated by a non-conducting medium, such 

 as the air, or, what is still better, a plate 

 of glass. Let the upper one P, commu- 



nicate, by a wire M, with the prime con- 

 ductor of the electrical machine ; and 

 let the lower one N, be insulated by 

 resting upon three glass supporters. 

 Let P be charged with a certain quan- 

 tity of electric fluid. The fluid natu- 

 rally contained in N, will be repelled by 

 the"fluid in P, and will quit the upper 

 surface of N in order to occupy its lower 

 surface. When this change has taken 

 place, let N be touched by a wire W, 

 establishing a communication between 

 it and the ground. All the fluid which 

 was accumulated in the lower surface 

 of N, will be earned off by the wire, 

 and the whole plate will thus be nega- 

 tive, or undercharged with fluid. The 



