362 Mr. Faraday's Researches in Electricity. {Series XL) 



charge of the carrier ball when applied to the apparatus 

 (1218.), unless that precaution be attended to. 



1233. I think it expedient, next in the course of these ex- 

 perimental researches, to describe some effects due to con- 

 duction, obtained with such bodies as glass, lac, sulphur, &c., 

 which had not been anticipated. Being understood, they will 

 make us acquainted with certain precautions necessary in in- 

 vestigating the great question of specific inductive capacity. 



1234. One of the inductive apparatus already described 

 (1187, &c.) had a hemispherical cup of shell-lac introduced, 

 which being in the interval between the inner ball and the 

 lower hemisphere, nearly occupied the space there; conse- 

 quently when the apparatus was charged, the lac was the di- 

 electric or insulating medium through which the induction 

 took place in that part. When this apparatus was first charged 

 with electricity (1198.) up to a certain intensity, as 400°, 

 measured by the Coulomb's electrometer (1180.), it sank 

 much faster from that degree than if it had been previously 

 charged to a higher point, and had gradually fallen to 400° ; 

 or than it would do if the charge were, by a second applica- 

 tion, raised up again to 400°; all other things remaining the 

 same. Again, if after having been charged for some time, as 

 fifteen or twenty minutes, it was suddenly and perfectly dis- 

 charged, even the stem having all electricity removed from it 

 (1203.), then the apparatus being left to itself, would gra- 

 dually recover a charge, which in nine or ten minutes would 

 rise up to 50° or 60°, and in one instance to 80^. 



1235. The electricity which in these cases returned from 

 an apparently latent to a sensible state, was always of the 

 same kind as that which had been given by the charge. The 

 return took place at both the inducing surfaces ; for if after the 

 perfect discharge of the apparatus the whole was insulated, 

 as the inner ball resumed a positive state the outer sphere ac- 

 quired a negative condition. 



1236. This effect was at once distinguished from that pro- 

 duced by the excited stem acting in curved lines of induction 

 (1203. 1232.), by the circumstance that all the returned elec- 

 tricity could be perfectly and instantly dischai'ged. It ap- 

 peared to depend upon the shell-lac within, and to be, in 

 some way, due to electricity evolved from it in consequence of 

 a previous condition into which it had been brought by the 

 charge of the metallic coatings or balls. 



1237. To examine this state more accurately, the appa- 

 ratus, with the hemispherical cup of shell-lac in it, was charged 

 for about forty-five minutes to above 600^ with positive elec- 



