SPECIFIC INDUCTIVE CAPACITY OP SHELL-LAC. 27 



(fig. 1.) between it and the inner ball; and then charges were divided in the 

 manner already described (1198. 1207.), each apparatus being used in turn to re- 

 ceive the first charge before its division by the other. As the apparatus were known 

 to have equal inductive power when air was in both (1209. 1211.), any differences re- 

 sulting 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 

 sought to be sustained. I have already referred to the precautions necessary in 

 making the experiments (1199, &c.) ; and with respect to the error which might be 

 introduced by the assumption of the peculiar state, it was guarded against, as far as 

 possible, in the first place, by operating quickly (1248.), and afterwards by using that 

 dielectric as glass or sulphur, which assumed the peculiar state most slowly, and in 

 the least degree (1239. 1241.). 



1257. The shell-lac hemisphere was put into app. i., and app. ii. left filled with air. 

 The results of an experiment in which the charge through air was divided and re- 

 duced by the shell-lac app. were as follows : 



App. i. Lac. App. ii. Air. 



Balls 255°. 

 0° . . . . 



.... 304° 

 .... 297 

 Charge divided. 

 113 ... . 



.... 121 

 . . . . after being discharged. 



.... 7 after being discharged. 



1258. Here 297°, minus 7°, or 290°, may be taken as the divisible charge of app. ii. 

 (the 7° being fixed stem action (1203. 1232.)), of which 145° is the half. The lac 

 app. i. gave 113° as the power or tension it had acquired after division ; and the air 

 app. ii. gave 121°, minus 7°, or 114°, as the force it possessed from what it retained 

 of the divisible charge of 290°. These two numbers should evidently be alike, and 

 they are very nearly so, far indeed within the errors of experiment and observation. 

 But these numbers diflfer very much from 145°, or the force which the half charge 

 would have had if app. i. had contained air instead of shell- lac ; and it appears that 

 whilst in the division the induction through the air has lost 176° of force, that 

 through the lac has only gained 113°. 



1259. If this difference be assumed as depending entirely on the greater facility 

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

 than that possessed by air, then this capacity for electric induction would be inversely 

 as the respective loss and gain indicated above ; and assuming the capacity of the air 

 apparatus as 1, that of the shell-lac apparatus would be 444, or 1*55. 



E 2 



