72 CORRELATION OF PHYSICAL FORCES. 



extreme cases where a trifling effect of conduction is appa- 

 rently produced without the usual elimination of substances at 

 the electrodes, the latter, when detached from the circuit, show, 

 by the counter-current which they are capable of producing 

 when immersed in a fresh liquid, that their superficial state has 

 been changed, doubtless by the determination to the surfaces 

 of minute layers of substances having opposite chemical cha- 

 racters. The question whether or not a minute conduction in 

 liquids can take place unaccompanied by chemical action, has 

 however been much agitated, and may be regarded as inter 

 apices of the science. 



Assuming for the moment electrolysis to be the only 

 known electrical phenomenon, electricity would appear to 

 consist in transmitted chemical action. All the evidence we 

 have is, that a certain affection of matter or chemical change 

 takes place at certain distant points of space, the change at 

 one point having a definite relation to the change at the other, 

 and being capable of manifestation at any intermediate points. 



If, now, the electrical effect called induction be examined, 

 the phenomena will be found equally opposed to the theory 

 of a fluid; and consistent with that of molecular polarisation. 

 When an electrified conductor is brought near another which 

 is not electrified, the latter becomes electrified by influence or . 

 induction, as it is termed, the nearest parts of each of these 

 two bodies exhibiting states of electricity of the contrary deno- 

 minations. Until this subject was investigated by Faraday, 

 the intervening non-conducting body or dielectric was sup- 

 posed to have no influence, and the effect was attributed to 

 the repulsion .at a distance of the electrical fluid. Faraday 

 showed that these effects differed greatly according to the 

 dielectric that was interposed. Thus they were more exalted 

 with sulphur than with shellac ; more with shellac than with 

 glass, &c. Matteucci, though differing from Faraday as to 

 the explanation he gave, added some experiments which prove 

 that the intervening dielectric is molecularly polarised. Thus 

 a number of thin plates of mica are superposed like a pack of 

 cards : metallic plates are applied to the outer facings, and 

 one of them electrified, so that the apparatus is charged like 

 a Leyden phial. Upon separating the plates with insulating 



