30 



ELECTRICITY. 



is brought irito contact "with the remote 

 end of the first cylinder P,(fig. 25), 

 which has been rendered positive by in- 

 duction. The fluid accumulated at this 

 end will now pass into the conductor, 

 and will remove to the most distant part 

 of the conductor. The transit will now 

 take place before actual contact, and 

 will be manifested by the appearance 

 of a spark when the bodies are brought 

 within the striking distance. The re- 

 moval of this fluid to a greater distance 

 will occasion a disturbance in the equi- 

 librium that had before been esta- 

 blished. The repulsion which that fluid 

 had excited, and which had contributed 

 to prevent any more fluid from being 

 propelled from the negative end N, is 

 now considerably weakened by the 

 greater distance at which it acts ; and 

 more fluid will leave the negative end, 

 which end will consequently become 

 more highly negative. This change of 

 distribution will again occasion a further 

 effect, by its reaction on the fluid in the 

 globe whence the action originally pro- 

 ceeded ; and another series of changes 

 and adjustments will follow, until a new 

 condition of equilibrium takes place, 

 and then the fluid will be at rest. 



(107.) Thus we learn that the effects 

 of induction on a conductor are aug- 

 mented by increasing its length; they 

 would, therefore, be greatest of all, if 

 we could give it infinite length : but the 

 same condition is attainable by placing 

 the conductor in communication with 

 the earth, which will accordingly carry 

 off all the fluid which the electrified 

 body is capable of expelling from the 

 nearest end. Accordingly, if we touch 

 with the finger, or with a metallic rod 

 held in the hand, the remote end of an 

 insulated conductor under the influence 

 of induction, we obtain a spark, more 

 or less vivid according to the intensity 

 of the electricity so induced ; and the 

 conductor so touched has now only one 

 kind of electricity, namely, the one op- 

 posite 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; because the actions of the re- 

 dundant fluid, and unsaturated matter 

 in the two bodies, exactly balance one 

 another. But it all the while really con- 

 tains less fluid than its natural share, in 

 consequence of the repulsive tendency 

 of the fluid in the body which produces 

 the induction ; and this negative state 



will readily become ' active, if the con- 

 ductor that has been touched be again 

 insulated, and then removed from the 

 influence of the former. This peculiar 

 condition of a body, in which its parts 

 are really undercharged or overcharged 

 with fluid, although, from the action of 

 electrical forces derived from bodies in 

 its vicinity, a state of equilibrium is 

 established, and no visible effect results, 

 has been denominated by Biot, dis- 

 guised electricity. 



(108.) It is also worthy of remark, 

 that if the communication between the 

 insulated conductor and another longer 

 conductor, or the earth itself, be made 

 at either end of the former, the same 

 effect will result, and the electric fluid 

 accumulated at its remote end will be 

 carried off by the longer conductor, 

 although, it will have, in one case, to 

 pass round through the end nearest to 

 the body which repels it. The opera- 

 tion which here takes place may be il- 

 lustrated by the motion of a fluid in a 

 syphon. A repulsive force is acting 

 upon the fluid, both in the shorter and 

 the longer column ; but with regard to 

 the motion of the fluid in the bent chan- 

 nel, the one force is in opposition to the 

 other, and the tendency of the fluid in 

 the longer column prevailing over that 

 in the shorter, will draw off the latter, 

 round the bend of the supposed syphon. 

 Thus in the bent conductor A N JP (fig. 

 27,), the repulsion exerted by the fluid 

 in E for that in the longer column N P, 



Fig. 27. 



being greater than its repulsion for that 

 in the shorter column N A, the fluid in 

 A will be carried over the bend N, not- 

 withstanding its tendency to move from 

 N towards A. 



(109.) We have hitherto supposed 

 the acting body to be positively electri- 

 fied; but precisely the same effects 

 would happen with regard to degree, 

 although opposite as to the species of 

 electricity, if it had been negatively elec- 

 trified : and the same explanations will 

 in every respect apply, with the requisite 

 substitution of the terms negative for 

 positive, and of attraction for repulsion, 

 and vice versa. A little reflection will 

 also easily show the application of the 



