8 Mr. Favaday and Dr. 1*. liiess un the Actiun of 



besides that, if an uninsulated wive was brought towards the cap 

 or gold-leaf, the charged posterior surface was discharged with a 

 spark, and the electrometer and shell-lac were left perfectly un- 

 charged. It is but a very small step to coat the posterior sur- 

 face with tinfoil beforehand, and then all the experiments can be 

 repeated, using contact with an uninsulated body instead of the 

 flame. Another step led to the coating of the anterior surface ; 

 the induction within the shell-lac between these surfaces and 

 perpendicular to them being precisely of the same kind as if 

 these coatings were away. If S, or the inducteous body, be 

 made one that cannot at a distance communicate a charge to the 

 posterior coating, being, for instance, an uninsulated metal ball 

 or plate, then each of these coatings has lor the time a polar 

 condition like that represented by np in the first diagram of 

 this letter, i. e. their anterior surfaces have negative charge, and 

 their posterior surfaces positive charge, when a positive inductric 

 body P is employed, and so long as the induction continues. 



I think you doubt the existence of specific inductive capacity. 

 You obtain the effects which I refer to it, but seem to explain 

 them by some act of conduction in the shell-lac, like that in in- 

 terposed metallic plates ; indeed, by the same act as that which 

 you suppose confers the assumed negative state on the anterior 

 surface of the shell-lac plate. Now if any of the induction effects 

 be due to such a conduction, this latter quality ought to appear 

 in very numerous and various forms of exj^eriment, especially if 

 time be taken into account. I have taken the plate of sulphui', 

 set it before P, applied the flame before the posterior surface, 

 removed the plate, applied the flame before the anterior surface, 

 and thus charged the sulphur negative and positive on the two 

 sides, as before described, in less than four seconds, and to a 

 considerable degree. That charge, thus quickly gained, the sul- 

 phur has retained apparently unimpaired for several minutes, and 

 at the expiration of several hours it was still strongly charged. 

 Kow how could any conduction within the mass of the sulphur 

 (of the nature of that which occurs in metals) have caused the 

 appearance at its surfaces of the two electricities in a moment or 

 two, and to twice the amount of what would have been evolved 

 if air had been there, which conduction was yet not competent to 

 effect their return in a period many hundred times as long? 

 We have I'cason to believe that induction is sensibly instanta- 

 neous; for if we take the sulphur plate coated over the middle 

 part of each face, and place a large metallic ball or plate for P 

 opposite to it, three successive contacts, one to touch P and 

 charge it, the second to touch for an instant the coating on the 

 posterior surface of the sulphur, and the third to touch P and 

 discharge it, are sufficient to put on the full inductive state 



