100 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XII.) 



having the same physical state and also the same pressure and the same temperature as 

 air, differ from it in specific gravity, in chemical qualities, and it may be in peculiar 

 relations, which not being as yet recognised, are purely electrical (1361.) ? 



1382. Into this question I can enter now only as far as is essential for the present 

 argument, namely, that insulation and inductive tension do not depend merely upon 

 the charged conductors employed, but also, and essentially, upon the interposed di- 

 electric, in consequence of the molecular action of its particles. 



1383. A glass vessel a (fig. 13.)=* was ground at the top and bottom so as to be 

 closed by two ground brass plates, b and c ; b carried a stuffing box, with a sliding 

 rod d terminated by a brass ball s below, and a ring above. The lower plate was 

 connected with afoot, stop-cock, and socket, e,/and o-; and also with a brass ball /, 

 which by means of a stem attached to it and entering the socket g, could be fixed at 

 various heights. The metallic parts of this apparatus were not varnished, but the 

 glass was well covered with a coat of shell-lac previously dissolved in alcohol. On 

 exhausting the vessel at the air-pump it could be filled with any other gas than air, 

 and, in such cases, the gas so passed in was dried whilst entering by fuzed chloride 

 of calcium. 



1384. The other part of the apparatus consisted of two insulating pillars, h and i, 

 to which were fixed two brass balls, and through these passed two sliding rods, k 

 and m, terminated at each end by brass balls ; n is the end of an insulated conductor, 

 which could be rendered either positive or negative from an electrical machine ; o 

 and p are wires connecting it with the two parts previously described, and ^ is a wire 

 which, connecting the two opposite sides of the collateral arrangements, also com- 

 municates with a good discharging train r (292.). 



1385. It is evident that the discharge from the machine electricity may pass either 

 between s and /, or S and L. The regulation adopted in the first experiments was to 

 keep s and / with their distance unchanged, but to introduce first one gas and then 

 another into the vessel a, and then balance the discharge at the one place against 

 that at the other ; for by making the interval at u sufficiently small, all the discharge 

 would pass there, or making it sufficiently large it would all occur at the interval v 

 in the receiver. On principle it seemed evident, that in this way the varying interval 

 u might be taken as a measure, or rather indication of the resistance to discharge 

 through the gas at the constant interval v. The following are the constant dimen- 

 sions. 



Ball* 0*93 of an inch. 



Ball S 0-96 of an inch. 



Ball / 2-02 of an inch. 



Ball L r95 of an inch. 



Interval t; 0*62 of an inch. 



1386. On proceeding to experiment it was found that when air or any gas was in 



♦ * The drawing is to a scale of ^. 



