Experimental investigation of the spirit manifestations, [electronic ...

APPENDIX. 455the poles of tho disturbing; apparatus^ neutralize each other intermediately.8np])0sin^j; the ponderable as ^vell as the inipondtirable matter in a perfectconductor to be susceptible of the polar arrangement, of which an electriiiedstate is thus represented to consist, non-conductors to be insusceptibleof such polar derangement; imperfect conductors may have a constitutionintermediate between metals and electrics.71. "When an electrical discharge is made through any space devoid ofair or other matter, it must then find its way solely by the polarization ofthe rare imponderable matter existing therein ; and consequently its corruscationsshould be proporlionably more diffuse, which is actually foundto be true ; but when gaseous ethcrco-ponderable atoms intervene, as inwire, they enable competent waves to exist within a narrower channel andto attain a greater intensity.72. I consider all bodies as insulators which cause discharges throughthem to be more difficult than through a vacuum, and which, by theirinterposition within a circuit, can prevent that propagation of the oppositelypolarizing undulations which would otherwise ensue. This furnishesa good mean of discrimination between insulators and conductors, thecriterion being that a discharge ensues more readily as there is more ofthe one and less of the other in the way : that the one leads the waveswhere they would not go, the other impedes their going where they wouldproceed. Both in the case of disruptive discharge through air, producinga spark, or of a deflagrating discharge through wire, causing itsexplosion,there is a dispersion of intervening ponderable particles ; and yet there isthis manifest discordancj^, that in one case the undulatory process of transferis assisted, in the other resisted. The waves follow the metallic filamentwith intense attraction, while they strive to get out of the way of thoseformed by the aeriform matter, as if repelled. Hence the term disruptive,from cUrumpo, to break through, was happily employed by Farraday todesignate spark discharges.73. The zigzag form of the disruptive spark shows that there is a tendencyin the aeriform particles to turn the waves out of that straightcourse, which, if unresisted or facilitated, they would naturally pursue.On the one hand, the aerial filaments being unsuitable for the conveyanceof the electric waves, these are forced by them out of the normal pathfirst in one direction, then in another; while, on the other hand, the finestmetallic filament furnishes a channel for the electric waves, so favourablethat this channel is pursued, although the consequent polarization of theconducting particles be so intense as to make them fly asunder with explosiveviolence. Even when a bell-wire has been dissipated by lightning, ithas been found to facilitate and determine the path of the discharge.74. The various forms of the electric spark, resulting from varying thegas through which it may be made to pass, agreeably to the researches ofFarraday, is explained by the supposition that the peculiarities of the sparkis partially the consequence of the polarizability of the gaseous atomsthrough which the discharge is made, and varies, accordingly, in its appearance.