362 Roijal Societi/ : Prof. Faraday's Experimental 



other. As the two instruments were known to have equal inductive 

 powers when air was contained in both, any deficiencies resulting 

 from the introduction of the shell-lac would show a peculiar action 

 in it, and, if unequivocally referable to a specific inductive influence, 

 would establish the point in question. 



The air apparatus being charged, and its disposable charge being 

 290°, this charge was divided between the two. After the division 

 the charge in the lac apparatus was 113°, and in the air apparatus 

 114°. From this it appears, that whilst by the division the induction 

 through the air lost 176°, that through lac gained only 113°. As- 

 suming that this difference depends entirely on the greater facility- 

 possessed by shell-lac of allowing or causing inductive action through 

 its substance than that possessed by air, then the capacity for electric 

 induction would be inversely as the respective loss and gain ; and as- 

 suming the capacity of the air apparatus as unity, that of the shell- 



1 7fi 

 lac apparatus would be — - or r55. 



113 



When the shell-lac apparatus was first charged, and then the 

 charge divided with the air apparatus, it appeared that the lac appa- 

 ratus, in communicating a charge of 118°, only lost a charge of 86°. 

 This result gives 1-37 as the capacity of the lac apparatus. 



Both these results, the author considers, require a correction ; 

 the former being in excess, the latter in defect. Applying this cor- 

 rection, they become 1*50 and 1'47. From a mean of these and se- 

 veral similar experiments, it is inferred that the inductive capacity of 

 the apparatus having the hemisphere of lac is to that with air as 

 1-50 to 1. 



As the lac only occupied one half of the apparatus containing it, 

 the other half being filled with air, it would follow from the foregoing 

 result, that the inductive capacity of shell-lac is to that of air as 

 2 to 1. 



From all these experiments and from the constancy of their results 

 the author deems the conclusion irresistible, that shell-lac does ex- 

 hibit a case of specific inductive capacity. 



Similar experiments with flint-glass gave its capacity 1*76 timesthat 

 of air. Using in like manner a hemisphere of sulphur, it appeared 

 that the inductive capacity of that substance was rather above 2*24 

 times that of air, and the author considers this result with sulphur 

 as one of the most unexceptionable. 



"With liquids, as oil of turpentine and naphtha, although the re- 

 sults are not inconsistent with the belief, that these liquids have a 

 greater specific inductive capacity than air, yet the author does not 

 consider the proofs as perfectly conclusive. 



A most interesting class of substances, in relation to specific in- 

 ductive capacity, the gases or aeriform bodies, next came under the 

 author's review. 



With atmospheric air, and likewise with pure oxygen, change of 

 density was found to occasion no change in the inductive capacity. 

 Nor was any change produced, either by an increase of temperature 

 or by a variation in the hygrometric state. 



