ELECTRICITY. 



the most generally applicable. Both 

 are, apparently, equally consistent 

 with facts ; but the existence of any 

 fluid, or form of matter, as the cause 

 of electrical phenomena, is at best 

 extremely problematical. 



" There are two series of distinct 

 phenomena represented by electrified 

 bodies : the one seems to result from 

 the accumulation of electricity upon 

 the surface of bodies ; they are com- 

 monly included under the term clcclri- 

 ciiy of tension, and are well exhibited 

 by the common electrical machine 

 and its prime conductor. It affects 

 all neighbouring bodies ; and they are 

 thrown by it into a polar electrical 

 state, by what is termed iyiduciion : 

 it has a tendency to pass off in sparks 

 through the air, or gradually to escape 

 from points. The thunder-storm fur- 

 nishes a magnificent specimen of this 

 state of electricity. The other state 

 of sensible electricity is that exhibit- 

 ed by electriaty in motion ; as when 

 a current of electricity is passing 

 through a w'ire or other conducting 

 medium : in this case a \ast quantity 

 of electricity may be concerned in the 

 phenomena without any apparent in- 

 tensity ; but while the current is con- 

 tinuous it produces magnetic phe- 

 nomena of a most extraordinary char- 

 acter ; and when the perfect conduct- 

 or is broken by the intervention of 

 certain other media, they suffer, in 

 some cases, chemical decomposition, 

 and in others become heated, and 

 even ignited. The phenomena of 

 electricity in motion are best exhib- 

 ited by the Voltaic apparatus. 



" In all electrical experiments, re- 

 markable differences are observed in 

 respect to the transfer of the electric 

 fluid through different bodies : some, 

 such as the metals, allow its free and 

 nearly unimpeded passage through 

 their substance ; while others receive 

 and retain it more superficially, such 

 as glass, resin, and other substances 

 v/hich exhibit attractive and repul- 

 sive powers when rubbed. Hence 

 the division of bodies into conductors 

 and non-conductors. 



"Many most important electrical 

 phenomena depend, apparently, upon 



induction, a subject which has been 

 ably studied by Faraday. We shall 

 here enter into such details only as 

 are required to render some of the 

 principal terms employed in discuss- 

 ing electrical phenomena intelligible. 

 " If P 4" represent a metallic sphere 

 in a highly positive 

 electric state, and N 

 P a metallic conduct- 

 or in its vicinity in- 

 sulated upon a glass 

 stem, it will be found that the ex- 

 tremity N of N P is negative, wliile 

 the other extremity, P, is -positive, 

 and that these opposite electricities 

 are greatest at the extremities of the 

 conductor, and gradually diminish to- 

 wards the centre line, C, which is 

 neutral. This extraordinary state of 

 excitation in N P is entirely depend- 

 ant upon the proximity of P -}- ; for 

 if P -f- be withdrawn, N P loses all 

 appearance of electricity ; and the 

 degree of excitement in it is directly 

 proportional to the extent to which 

 P 4" is excited, and (within certain 

 limits) to its nearness to N ; so that 

 fluctuations in the electricity of N P 

 will be observed in proportion as P -|- 

 is brought towards or removed from 

 N, provided they are not brought into 

 contact, and that no spark passes. 

 These phenomena have been theoret- 

 ically explained upon the supposition 

 that the free electricity in P -|- dis- 

 turbs the equilibrium of the natural 

 electricity of N P, and, by repelling it 

 from N to P, leaves the former minus 

 and the latter plus. Or, if we assume 

 the existence of two electric fluids, 

 then the free positive electricity of 

 P -f- repels the positive fluid of N P, 

 and attracts its negative fluid, throw- 

 ing it into an electro-polar state. If 

 N P, instead of being insulated, be 

 connected by its extremity, P, with 

 the ground, the accumulation at P 

 is prevented, while N retains its de- 

 ficient or negative state ; or, upon the 

 other theory, the positive fluid at P is 

 neutralized by a supply of negative 

 fluid from the earth ; and if, after 

 having effected this by momentarily 

 touching N P with the finger, we sud- 

 denly remove P -\-, the insulated con- 



