254 PLYMOUTH INSTITUTION. 



bodies which have experienced any such a change in their electrical 

 states exert an attractive influence upon indifferent matter which 

 is found to increase in the proportion of the square either of the 

 increased change, or of the diminished distance at which any 

 determinate change operates; to account for this apparently 

 disproportionate increase of effect, the lecturer took into account 

 the effect of induction, which would be quite sufficient to account 

 for it. When an electrified body is opposed to an unelectrified 

 body, at any fixed distance, attraction is immediately apparent; 

 if the distance be diminished one half, it might be expected that 

 the attractive force would only be doubled ; this he shewed would 

 be pretty nearly the case, provided the attracted body were of 

 small dimensions, and perfectly insulated ; but when it was of 

 any considerable size, half the distance produced four times the 

 effect, one third the distance nine times the effect, &c. It is a 

 law of electricity that all bodies, whether in a positive or negative 

 state, will attract bodies of an opposite state with more power 

 than those which are perfectly neutral ; and when an electrified 

 body is opposed to a neutral body of a considerable size, its first 

 effect is to induce in that portion nearest to itself an electricity 

 opposite to that with which it is itself charged : for example — if 

 it be positive, it drives the natural electricity of the opposed 

 conductor into its extreme end, and thereby rendering the proxi- 

 mate surface negative, prepares for itself as it were a suitable 

 reception. The two bodies then attract each other with a given 

 force; now if the substance between these be diminished one half 

 the attraction of the electrified conductor would be doubled, if 

 acting on perfectly neutral matter; but the inductive effect 

 produced by this approximation would be doubled on the unelec- 

 trified conductor, which would consequently also attract with 

 twice the force; hence, the amount of the attraction between the 

 two bodies would be 2, multiplied by 2,=4 ; again, if the distance 

 be diminished to one third, the attractive power of the electrified 

 conductor would be increased three times ; but the inductive 

 effect being also trebled, the opposed conductor would also 

 attract with three times the force, consequently the amount of 

 attraction will be 3 multiplied by 3,=9, the square of the 

 increased elementary power; thus, it was evident that this phe- 

 nomenon was not an elementary law, but resulted merely from 

 an increase of the attractive power acting on neutral matter, 

 but upon a superinduced attractive power of an opposite kind, 

 and equally powerful. 



