OF CERTAIN ELECTRICAL SUBSTANCES. 
167 
7. In order to obtain a given measured charge, sparks were taken upon insulated 
metallic carrier plates A, A', fig. 5 and 6, from the knob of a jar K, fig. 7, charged to 
a given intensity, and the electricity was deposited on the coating c, fig. 4. But as 
the repeated transfer of one plate, considered as a unit of charge, would be attended 
by a loss of electricity upon a great number of measures, in consequence of some re- 
siduary electricity being again brought off at each contact, I employed larger carrier 
plates, A, fig. 5, which could at once take up, under the same intensity, double, triple, 
&c. the quantity contained on the smaller one, A, fig. 5, and thus deposit at once, to- 
gether with the plate, a given number of measures on the coated substance c*. 
8. I found it, however, desirable in some cases to observe the intensity of the half 
or quarter of the charge collected on the large transfer plate A, fig. 5, by dividing 
and subdividing it with a second equal and similar neutral plate B, fig. 8. Thus, 
supposing the whole disc to contain under a given intensity a quantity equal to eight 
measures, we may immediately obtain four measures by a momentary contact with 
an insulated neutral and similar plate B, fig. 8, and two measures by a second con- 
tact. We are thus enabled to work with lower charges in certain cases ; since from 
the intensity of the half, or quarter of a charge, we can, by known laws of electrical 
action, deduce the intensity of the whole. We avoid in this way the dissipation 
which is liable to occur under a high intensity, and hence arrive at a more correct 
result. The carrier plates employed were of various kinds, and were constructed 
either of metallic substances or of gilded wood, and were insulated on very long 
slender rods of glass covered with lac, as represented in figs. 5 and 6. 
9. The jar K, fig. 7, is supported on a varnished glass rod K ; it contains about 100 
square inches of coating, and was charged with fifteen measures of a small unit jar, 
containing about ten square inches, the measuring balls being set at 2 of an inch 
apart. When charged, it was removed from the machine, and the connection of the 
outer coating with the ground withdrawn, so as to leave it well insulated. As often 
as a charge was drawn from the knob by either of the carrier plates A, A', an equi- 
valent charge was communicated to the outer or negative coating, and thus repeated 
measured charges of the same intensity were obtained. The state of this jar was 
examined from time to time by means of a small carrier plate of three inches in dia- 
meter, and a second electrometer E', fig. 9. As long as the jar could charge this 
plate to an intensity of 10°, as measured by the electrometer, the discs m, n, fig. 9, 
being at a given distance, so long it was deemed in a fit state for experiment. When 
the intensity fell below this point, the original charge of fifteen unit measures was 
again restored. 
10. The electrometer E, fig. 4, has been fully described in the Philosophical Trans- 
actions for 1839f ; it is therefore only requisite to state, that by means of a hydro- 
static counterpoise v, acting over a delicately hung wheel W, we obtain a continued 
and uniform balance to the attractive force between the opposed discs f, m, ope- 
* Philosophical Transactions for 1834, p. 235. t P- 215. 
