496 Intelligence and Miscellaneous Articles. 



•would be necessary to say that they have all the same inductive 

 capacity — if the use of this phrase (which, as I think, does not ex- 

 press a distinct property) ought not to be completely abandoned. 



In all the experiments of which I have hitherto spoken, the arma- 

 tures of the fulminating panes were directly applied to the insula- 

 ting disc ; in this manner different insulating discs could be com- 

 pared 'with each other ; but insulating bodies could not be compared 

 with metals. To establish this comparison, I modified the arrange- 

 ment of the fulminating panes. I separated the metallic armatures 

 from the insulating disc by small layers of air of constant thickness. 

 By working in this manner, and using as intermediate discs metallic 

 plates of different thicknesses, I found that this thickness does not 

 perceptibly influence the charge of the condenser, at least so long 

 as this disc is very thin as compared with the diameter of the discs. 

 I found, secondly (and this point appears to me important), that the 

 limiting: charge is not modified by substituting a metallic disc for an 

 insulating one. In the case of an insulating disc, the limiting charge 

 is only obtained after the lapse of a considerable time, varying with 

 the nature and thickness of the insulator, while with the metallic 

 disc the limiting charge is established in an inappreciable time. 



When the intermediate disc is an insulator in immediate contact 

 with the armatures, the limiting charge depends, as I have just said, 

 neither on the nature nor thickness of the insulating body ; but it 

 may vary considerably with another element, which has not hitherto 

 been taken into account, and which is really an important element : 

 this is the external resistance of the insulator. This resistance arises 

 almost entirely, if not quite, from the small layer of air always 

 interposed between the insulating disc and its armatures, even when 

 the surfaces have been planed with the greatest care ; and it varies 

 singularly with the hygrometric state of the surrounding air. This 

 circumstance makes the experiments in question somewhat delicate. 

 In fact, from what I have said, when two fulminating panes formed 

 from insulating discs of different nature and thickness are compared, 

 it is indispensable that they be placed in the same hygrometric con- 

 ditions. 



From the whole of my researches, it appeared to follow that insu- 

 lating solid bodies, submitted to the influence of electricity, behave 

 exactly like metals, and consequently the inductive capacity is not 

 distinct from the conductibility. I am not ignorant that the condi- 

 tions under which I experimented are extremely different from 

 those indicated by the illustrious philosopher who propounded the 

 notion of inductive capacity. Instead of charging to saturation 

 the Leyden jar with which he worked, Mr. Faraday charged it as 

 rapidly as possible, so as to remove the effects of the conductibility 

 of the dielectric, which he only considers as a disturbing cause. But 

 this mode of view does not seem to me to rest on decisive reasons. 

 1 have limited myself, in the research of which I am giving the general 

 results, to considering the permanent state ; Mr. Faraday, on the 

 contrary, has only occupied himself with the variable state ; but it is 

 difficult to admit that the distribution of electricity should not be 

 ruied by the same principles in both cases. I propose to revert to 

 the phenomena of the variable state. — Comptes Rendus, Sept. 8, 1S62. 



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