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VI. Supplemental^ Note to Experimental Researches in Electricity. — Eleventh Series. 

 By Michael Faraday, Esq. D.C.L. F.R.S., Fullerian Prof. Cheni. Royal Insti- 

 tution, Corr. Memb. Royal and Imp. Acadd. of Sciences, Paris, Peiersburgh, 

 Florence, Copenhagen, Berlin, 8^c. 8^c. 



Received March 29, 1838. 



1307- A HAVE recently put into an experimental form that general statement of 

 the question of specific inductive capacity which is given at No. 1252 of Series XL, 

 and the result is such as to lead me to hope the Council will authorise its addition to 

 the paper in the form of a supplementary note. Three circular brass plates, about 

 five inches in diameter, were mounted side by side upon insulating pillars ; the 

 middle one, A, was a fixture, but the outer plates B and C were moveable on slides, 

 so that all three could be brought with their sides almost into contact, or separated 

 to any required distance. Two gold leaves were suspended in a glass jar from insu- 

 lated wires ; one of the outer plates B was connected with one of the gold leaves, and 

 the other outer plate with the other leaf. The outer plates B and C were adjusted at 

 the distance of an inch and a quarter from the middle plate A, and the gold leaves 

 were fixed at two inches apart ; A was then slightly charged with electricity, and the 

 plates B and C, with their gold leaves, thrown out of insulation at the same time, and 

 then left insulated. In this state of things A was charged positive inductrically, and 

 B with C negative inducteously ; the same dielectric, air, being in the two intervals, 

 and the gold leaves hanging, of course, parallel to each other in a relatively unelec- 

 trified state. 



1308. A plate of shell-lac three quarters of an inch in thickness, and four inches 

 square, suspended by clean white silk thread, was very carefully deprived of all 

 charge (1203.), so that it produced no effect on the gold leaves if A were uncharged, 

 and then introduced between plates A and B ; the electric relation of the three plates 

 was immediately altered, and the gold leaves attracted each other. On removing the 

 shell-lac this attraction ceased ; on introducing it between A ahd C it was renewed ; 

 on removing it the attraction again ceased ; and the shell-lac when examined by a 

 delicate Coulomb electrometer was still without charge. 



1 309. As A was positive, B and C were of course negative ; but as the specific in- 

 ductive capacity of shell-lac is about twice that of air (1270.), it was expected that 

 when the lac was introduced between A and B, A would induce more towards B than 

 towards C ; that therefore B would become more negative than before towards A, and 



