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VIII. Experimental Researches in Electricity. — Thirteenth Series. By Michael 

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

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

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



Received February 22,— Read March 15, 1838. 



§. 18. 0?i Induction (continued). ^ ix. Disi^ptive discharge (continued) — 

 Peculiarities of positive and negative discharge either as spark or 

 brush — Glow discharge — Dark discharge. — ^ x. Convection, or car- 

 rying discharge. ^ xi. Relation of a vacuum to electrical pheno- 

 mena. §.19. Nature of the electrical current. 



^ ix. Disruptive discharge (continued). 



1480. J-iET us now direct our attention to the general difference of the positive and 

 negative disruptive discharge, with the object of tracing, as far as possible, the cause 

 of that difference, and whether it depends on the charged conductors principally, or 

 on the interposed dielectric ; and as it appears to be great in air and nitrogen (1476.), 

 let us observe the phenomena in air first. 



1481. The general case is best understood by a reference to surfaces of consider- 

 able size rather than to points, which involve (as a secondary effect) the formation 

 of currents (1562.). My investigation, therefore, was carried on with balls and ter- 

 minations of different diameters, and the following are some of the principal results. 



1482. If two balls of very different dimensions, as for instance one, half an inch, 

 and the other three inches, in diameter, be arranged at the ends of rods so that either 

 can be electrified by a machine and made to discharge by sparks to the other, which 

 is at the same time uninsulated; then, as is well known, far longer sparks are obtained 

 when the small ball is positive and the large ball negative, than when the small ball 

 is negative and the large ball positive. In the former case, the sparks are 10 or 12 

 inches in length ; in the latter an inch or an inch and a half only. 



1483. But previous to the description of further experiments, I will mention two 

 words, for which with many others I am indebted to a friend, and which I think it 

 would be expedient to introduce and use. It is important in ordinary inductive ac- 

 tion, to distinguish at which charged surface the induction originates and is sustained: 

 i. e. if two or more metallic balls, or other masses of matter, are in inductive relation, 

 to express which are charged originally, and which are brought by them into the 



