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VII. Experimental Researches in Electricity/. — Twelfth Series. By Michael 

 Faraday, Esq., D.C.L. F.R.S. Fullerian Prof. Chem. Royal Institution, Corr. 

 Memh. Royal and Imp. Acadd. of Sciences, Paris, Petershurgh, Florence, Copen- 

 hagen, Berlin, 8^c. S^c. 



Received January 11, — Read February 8, 1838. 



§.18. On Induction {continued). ^ vii. Conduction, or conductive discharge. 

 ^ viii. Electrolytic discharge. ^ ix. Disruptive discharge — Insula- 

 tion — Spark — Brush — Difference of discharge at the positive and ne- 

 gative surfaces of conductors. 



1318. 1 PROCEED now, according to my promise, to examine, by the great facts 

 of electrical science, that theory of induction which I have ventured to put forth 

 (1165. 1295. &c.). The principle of induction is so universal that it pervades all 

 electrical phenomena ; but the general case which I purpose at present to go into 

 consists of insulation traced into and terminating with discharge, with the accompa- 

 nying effects. This case includes the various modes of discharge, and also the con- 

 dition and characters of a current ; the elements of magnetic action being amongst 

 the latter. I shall necessarily have occasion to speak theoretically, and even hypo- 

 thetically ; and though these papers profess to be experimental researches, I hope 

 that, considering the facts and investigations contained in the last series in support 

 of the particular view advanced, I shall not be considered as taking too much liberty 

 on the present occasion, or as departing too far from the character which they ought 

 to have, especially as I shall use every opportunity which presents itself of returning 

 to that strong test of truth, experiment. 



1319. Induction has as yet been considered in these papers only in cases of insu- 

 lation ; — opposed to insulation is discharge. The action or effect which may be ex- 

 pressed by the general term discharge, may take place, as far as we are aware at 

 present, in several modes. Thus, that which is called simiply conduction involves no 

 chemical action, and apparently no displacement of the particles concerned. A se- 

 cond mode may be called electrolytic discharge ; in it chemical action does occur, 

 and particles must, to a certain degree, be displaced. A third mode, namely, that 

 by sparks or brushes, may, because of its violent displacement of the particles of the 

 dielectric in its course, be called the disruptive discharge ; and a fourth may, perhaps, 

 be conveniently distinguished for a time by the words convection, or carrying discharge, 

 being that in which discharge is effected either by the carrying power of solid par- 



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