6 Mr. Faraday and Dr. P. Riess on the Action of 



much the strongest when the posterior face was in contact with 

 the cap, showing, so far as that went, that the charge was really 

 on that face. 



According to my view of induction, that face of the plate had 

 been charged negatively by the flame ; for the portion of the 

 induction between P and the flame could be destroyed by the 

 convection dependent on the latter where air only intervened 

 between it and towards P ; but as the air in the direction of the 

 conduction terminated at the posterior surface of the shell-lac, so 

 the flame could convey its state of charge to that surface only, 

 the insulating power and solidity of the shell-lac preventing 

 fui-ther changes in that direction ; hence the result already de- 

 scribed. As the flame had power to charge the posterior surface, so 

 it can discharge it, and accordingly by moving the flame for a 

 moment parallel to that surface, and about an inch from it, the 

 plate will be entirely discharged. The previous state of negative 

 charge on the posterior surface of the plate will, if wished, remain 

 for a minute, or two minutes, or even five or ten ; and yet the 

 momentary use of the flame discharges it entirely. The result 

 accords perfectly with my view, but, as it appears to me, is en- 

 tu'ely opposed to yom-s. Nor can I see how the assumption of 

 any degree of conduction in the shell-lac, compatible with the 

 acknowledged facts dependent on its insulating powers, can ex- 

 plain the result. 



But it may be said, that the second application of the flame, 

 instead of discharging the negative posterior surface, has really 

 charged it positively to an amount equal to the supposed nega- 

 tive charge on the anterior surface, and so covers the efl^ect of 

 the latter more or less according to the thickness of the plate ; 

 and then the question is, is the plate entirely discharged, or is it 

 now doubly charged, i. e. with one surface positive and the other 

 negative ? I find it to be entirely discharged ; for if I place either 

 surface on the cap ])late of the gold-leaf electrometer, and then 

 carefully bring an uninsulated metallic plate to the other surface, 

 I find no effect on the electrometer; whereas there would be such 

 an efl'ect if the plate had been charged as a Leyden jar. 



Or it may be supposed that the second application of the flame, 

 though applied ou the posterior side of the shell-lac, has some- 

 how or other discharged the negative anterior surface. This is 

 easily shown not to be the case, by the ajjplication of the flame 

 on the anterior side, and then still stronger proofs than those 

 already obtained appear against your view and for mine; for 

 according to my view, such an application of the flame ought to 

 cause the anterior face to acquire a positive charge, inasmuch as 

 a second case of induction is set up, in M'hich the posterior nega- 

 tively charged face of the shell-lac is the inductric body, to which 



