168 
MR. SNOW HARRIS ON THE SPECIFIC INDUCTIVE CAPACITIES 
rating on the opposite arm of the wheel ; whilst an index i o attached to the wheel 
registers the force in degrees of a graduated arc x o y. 
1 1 . These preliminary explanations being understood, the following experiments 
will be fully comprehended. 
Exp. 1. A circular coated plate of shell-lac, N, fig. 4, being placed on the insulated 
rod k, and its upper coating c connected with the electrometer disc m, one measure 
of electricity was deposited on it, by placing one of the small charged carrier discs 
immediately on the coating. In order to find the intensity by the electrometer at 
a constant distance of - 5 of an inch between the attracting discs m,f, and to which 
they had been previously adjusted when the index was at zero, the hydrostatic 
counterpoise was lowered by means of the screw S until the index was again brought 
to zero of the arc ; whatever force, therefore, was now operating between the discs 
m,f, was operating at the given distance of ’5 of an inch. To find this force in de- 
grees, the deposited electricity was discharged ; the index then declined or fell back 
in the direction o y, a certain number of degrees, showing the force or intensity re- 
quired. 
Thus the deposition of one measure on the insulated plate c evinced an intensity of 
4°, and according to the known law of accumulation two measures evinced an inten- 
sity of 16°, and so on, as the square of the quantity deposited* up to the limit of 
charge. Now this intensity was found to be the same, or nearly so, with every insu- 
lating substance tried, whether shell-lac, or air, or brimstone, or any other good in- 
sulator, and was very little different whether insulated as a single plate or as a 
double plate, such as represented in fig. 2. An intensity of 4° was therefore taken 
as the free charge, and as indicating one measure, supposing it all active on the elec- 
trometer, and uncondensed by induction through any given medium. 
Exp. 2. The under coating d being now connected with the electrometer disc m, 
and 1, 2, 3, &c. measures successively deposited on the coating c, the respective in- 
tensities developed in the opposite coating d by induction were, for one measure 3°, 
two measures 12°, three measures 2 7 °, and so on up to the limit of inductive develop- 
ment in the opposed plate -f~. 
12. Now this direct induction was observed to be the same, or very nearly so, whether 
operating through air or through lac, or any other solid insulator; thus confirming, 
together with the preceding experiment, Dr. Faraday’s observation relative to shell- 
lac (1255.), viz. “That its solid condition enabled it to retain the excited particles in 
a permanent position, but that appeared to be all, for these particles acted just as 
freely through the shell-lac on one side as through the air on the other.” He did 
not find, however, every substance bear a rigid examination in this respect ; yet the 
substances which I have tested all evinced nearly the same freedom, as measurable 
by the charges and electrometer employed. 
Exp. 3. The under coating d, fig. 4, being connected with the ground, and the 
* Philosophical Transactions for 1834, p. 219 and 221. t Ibid. 1839, p. 223 and 224. 
