he two intervals, and the gold leaves hanging,
of course, parallel to each other in a relatively unelectrified state.

1308. A plate of shell-lac three-quarters of an inch in thickness, and four
inches square, suspended by clean white silk thread, was very carefully
deprived of all charge (1203.) (so that it produced no effect on the gold
leaves if A were uncharged) and then introduced between plates A and B; the
electric relation of the three plates was immediately altered, and the gold
leaves attracted each other. On removing the shell-lac this attraction
ceased; on introducing it between A and C it was renewed; on removing it
the attraction again ceased; and the shell-lac when examined by a delicate
Coulomb electrometer was still without charge.

1309. As A was positive, B and C were of course negative; but as the
specific inductive capacity of shell-lac is about twice that of air
(1270.), it was expected that when the lac was introduced between A and B,
A would induce more towards B than towards C; that therefore B would become
more negative than before towards A, and consequently, because of its
insulated condition, be positive externally, as at its back or at the gold
leaves; whilst C would be less negative towards A, and therefore negative
outwards or at the gold leaves. This was found to be the case; for on
whichever side of A the shell-lac was introduced the external plate at that
side was positive, and the external plate on the other side negative
towards each other, and also to uninsulated external bodies.

1310. On employing a plate of sulphur instead of shell-lac, the same
results were obtained; consistent with the conclusions drawn regarding the
high specific inductive capacity of that body already given (1276.).

1311. These effects of specific inductive capacity can be exalted in
various ways, and it is this capability which makes the great value of the
apparatus. Thus I introduced the shell-lac between A and B, and then for a
moment connected B and C, uninsulated them, and finally left them in the
insulated state; the gold leaves were of course hanging parallel to each
other. On removing the shell-lac the gold leaves attracted each other; on
introducing the shell-lac between A and C this attraction was _increased_,
(as had been anticipated from theory,) and the leaves came together, though
not more than four inches long, and hanging three inches apart.

1312. By simply bringing the gold leaves nearer