294) Mr. Faraday's Experimental Researches in Electricity. 



1194;. The apparatus when in order could easily be ex- 

 hausted of air and filled with any given gas ; but when that 

 gas was acid or jtlkaline, it could not properly be removed by 

 the air-pump, and yet required to be perfectly cleared away. 

 In such cases the apparatus was opened and cleared; and 

 with respect to the inner ball ^, it was washed out two or 

 three times with distilled water introduced at the screw hole, 

 and then being heated above 212°, air was blown through to 

 render the interior perfectly dry. 



1195. The inductive apparatus described is evidently a 

 Leyden phial, with the advantage, however, of having the di- 

 electric or insulating medium changed at pleasure. The balls 

 h and B, with the connecting wire i, constitute the charged 

 conductor, upon the surface of which all the electric force is 

 resident by virtue of induction (1178.). Now though the 

 largest portion of this induction is between the ball h and the 

 surrounding sphere a a, yet the wire i and the ball B deter- 

 mine a part of the induction from their surfaces towards the 

 external surrounding conductors. Still, as all things in that 

 respect remain the same, whilst the medium within at o o, may 

 be varied, any changes exhibited by the whole apparatus will 

 in such cases depend upon the variations made in the interior ; 

 and it was these changes I was in search of, the negation or 

 establishment of such dijfFerences being the great object of my 

 inquiry. I considered that these differences, if they existed, 

 would be most distinctly set forth by having two apparatus of 

 the kind described, precisely similar in every respect; and 

 then, different insulating media being within, to charge one 

 and measure it, and after dividing the charge with the other, 

 to observe what the ultimate conditions of both were. If in- 

 sulating media really had any specific differences in favouring 

 or opposing inductive action through them, such differences, 

 I conceived, could not fail of being developed by such a pro- 

 cess. 



1196. I will wind up this description of the apparatus, and 

 explain the precautions necessary in their use, by describing 

 the form and order of the experiments made to prove their 

 equality when both contained common air. In order to fa- 

 cilitate reference I will distinguish the two by the terms App. 

 i, and App. ii. 



1 197. The electrometer is first to be adjusted and examined 

 (1184.), and the app. i. and ii. are to be perfectly discharged. 

 A Leyden phial is to be charged to such a degree that it would 

 give a spark of about one-sixteenth or one-twentieth of an inch 

 in length between two balls of half an inch diameter ; and the 

 carrier ball of the electrometer being charged by this phial, is 



