828 



ELECTRICITY. 



hcyond a certain distance from the direct line of pro- 

 jection. But this very velocity will carry the par- 

 ticles, that liappen to have deviated most, somewhat 

 beyond the point to which they are attracted ; while 

 the attraction to this latter point will tend to deflect 

 them from the line of their path, and gradually turn 

 them back, so that they will arrive at the point of 

 attraction by very different patlis, and some even by 

 a retrograde motion. Hence, while, in the first 

 case, they form a diverging cone of rays, in the latter 

 ihey must be distributed on all sides of the point, 

 like the rays of a star. 



VI. Active electricity, existing in any substance, 

 tends always to induce the opposite electrical state in 

 the bodies that are near it. Now, it is impossible to 

 induce one electrical state in any body, without, at 

 the same time, producing the opposite state in the 

 same body, or in the one which is immediately con- 

 tiguous. It follows, therefore, that if the bodies sub- 

 jected to the inductive influence are non-conductors, 

 although the tendency to produce the opposite elec- 

 tricity exists, yet, in consequence of the immobility 

 of the fluid, it can produce no visible change.- In 

 proportion as the body opposes less resistance to the 

 passage of electricity, the operation of the disturbing 

 force becomes sensible. For example, in the case of 

 a positively charged electric, acting by induction on 

 an insulated conducting body, the redundant fluid in 

 the former must tend to repel all the fluid contained 

 in the latter ; a portion of this fluid must, therefore, 

 be driven from the side adjacent to the first body, 

 towards the remoter side. The adjacent side will 

 thus be rendered negative ; the remoter side, positive. 

 But this will take place to a certain extent only ; for 

 there is a limit at which the repulsion of the fluid 

 accumulated at the remote end will just balance the 

 repulsion of the fluid in the electric, added to the 

 attraction of the under-saturated matter, in the near 

 end ; and when the limit has been attained, the flow 

 of electric fluid from the near to the remote end of 

 the body will cease, and an equilibrium will be esta- 

 blished. Experiment fully confirms this theory, as 

 may be seen by bringing a cylinder of metal of some 

 length, with rounded ends, near an electrified globe 

 of glass, taking care that it be not sufficiently near to 

 receive any quantity of electricity by transference. 

 By means of the electrometer of Coulomb, we per- 

 ceive that the part of the conductor nearest to the 

 electric is negative, and the part most remote is 

 positive ; while, about the middle of the cylinder, the 

 body is in a neutral state. The electricity is found 

 to dimmish as we proceed from either extremity to- 

 wards this point of neutrality. These remarkable 

 effects are solely the result of the action of electri- 

 city at a distance ; for they take place in an equal 

 degree, whatever non-conducting substance may be 

 interposed between the bodies exerting this influence 

 on one another. But in an experiment, where the 

 acting body, instead of being an electric, is a con- 

 ducting body, the electrical state which the globe 

 induces on the cylinder must react upon its own elec- 

 tricity. The negative electricity, that is, the under- 

 saturated matter at the nearer end of the cylinder, 

 must exert a tendency to induce positive electricity 

 in the globe, and more especially upon the side next 

 the cylinder ; that is, it will tend, by its attraction 

 for the fluid, to draw it to that side, and thus render 

 it still more highly positive than it was before. This 

 can only be done at the expense of the other side, 

 from which the fluid must be taken, and which is 

 therefore rendered less charged with fluid, that is, 

 less positive than before. But this new distribution 

 of the electric fluid in the globe, by increasing the 

 positive state of the side next the cylinder, tends to 

 augment its inductive influence on the fluid in the 



cylinder ; that is, to drive an additional quantity of 

 fluid from the negative to the positive end. This 

 must be followed in turn by a corresponding re- 

 action on the globe, and so on, constituting a 

 series of smaller adjustments, until a perfect equili- 

 brium is established in every part. This reasoning 

 is fully established by experiment. All that is re- 

 quired for its illustration is simply to furnish the me- 

 tallic globe, insulated and charged with positive 

 electricity, with electroscopes upon its opposite sur- 

 faces. No sooner do we bring near to it a conducU 

 ing body, than the balls of the electroscope, at the 

 side most distant from that body, begin to collapse, 

 while those at the nearer side diverge to a greater 

 degree than before ; thus showing the nature of the 

 reflex operation of the induced electricity of the 

 conductor upon the Ixxly from which the induction 

 originated. In all the clianges thus alluded to, there 

 has been no transfer of electricity from either of the 

 bodies to the other, as is most satisfactorily proved 

 from the circumstance, that the mere removal of the 

 bodies to a distance from one another is sufficient to 

 restore each of them to their original state. The 

 globe remains as perfectly electrified as before ; the 

 cylinder returns to its condition of perfect neutrality ; 

 and the experiment may be repeated as often as we 

 please, without any variation in the phenomena. 

 This would not be the case, however, if the cylinder 

 were divided in the middle, and one or both of the 

 parts were removed separately, while, they still re- 

 mained under the influence of the globe. The return 

 of the electric fluid from the positive to the negative 

 end being thus prevented, each part will retain, after 

 its separation, the electricity which had been induced 

 upon it ; the nearer portion will remain negative, 

 the remoter one positive. If the division had been 

 in three parts, the middle part only would have been 

 neutral. It is found by experiment, that the effects 

 of induction on a conductor are augmented by in- 

 creasing its length ; and they become as great as 

 possible, by placing the conductor in communication 

 with the earth, which carries off all the fluid the 

 electrified body is capable of expelling from the 

 nearest end. A conductor under the influence of 

 induction, between which and the earth a communi- 

 cation has been made, by touching the remote end 

 with a metallic rod held in the hand, possesses but 

 one kind of electricity, namely, the one opposite to 

 that of the electrified body which is acting upon it. 

 The part touched is brought into a state in which it 

 appears to be neutral, as long as it remains in the 

 vicinity of the electrified body; but it really contains 

 less fluid than its natural share ; and this will imme- 

 diately become apparent, if the conductor that has 

 been touched be again insulated, and then removed 

 from the influence of the body producing the induc- 

 tion. This peculiar condition of a body, in which 

 its parts are really undercharged or overcharged with 

 fluid, although, from the action of electric forces de- 

 rived from bodies in its vicinity, a state of equilibrium 

 is established, and no visible effect results, has been 

 denominated by Biot, disguised electricity. We have 

 hitherto supposed the acting body to be positively 

 electrified ; but precisely the same effects would 

 tiappen with regard to the degree, although opposite 

 as to the species of electricity, if it had been nega- 

 tively electrified Our knowledge of the induction 

 of electricity enables us to understand why bodies, 

 between which it takes place, should attract one 

 another. For the action of the adjacent sides, which 

 are brought into opposite electrical states, is greater 

 than, the action of those sides which are in the same 

 lectrical states, and which are more distant ; hence 

 ;he attractive force always exceeds the repulsive. 

 The most convenient mode of obtaining an acciunula- 



