41 



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

 176 



lac apparatus would be 1'55. 



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 tol. 



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 gaveits capacity 1 "76 times that 

 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. 



The details are then given of a very elaborate series of experiments 

 with atmospheric air, oxygen, hydrogen, nitrogen, muriatic acid, 

 carbonic acid, sulphurous acid, sulphuretted hydrogen, and other 

 gases, undertaken with the view of comparing them one with an- 

 other under a great variety of modifications. Notwithstanding the 

 striking contrasts of all kinds which these gases present, of property, 

 of density, whether simple or compound, anions or cations, of high 

 or low pressure, hot or cold, not the least difference in their capacity 

 to favour or admit electrical induction through them could be per- 

 ceived. Considering the point established, that in all these gases 

 induction takes place by an action of contiguous particles, this is 

 the more important, and adds one to the many striking relations 

 which hold among bodies having the gaseous form. 



