tricity, which in these cases returned from an apparently
latent to a sensible state, was always of the same kind as that which had
been given by the charge. The return took place at both the inducing
surfaces; for if after the perfect discharge of the apparatus the whole was
insulated, as the inner ball resumed a positive state the outer sphere
acquired a negative condition.

1236. This effect was at once distinguished from that produced by the
excited stem acting in curved lines of induction (1203. 1232.), by the
circumstance that all the returned electricity could be perfectly and
instantly discharged. It appeared to depend upon the shell-lac within, and
to be, in some way, due to electricity evolved from it in consequence of a
previous condition into which it had been brought by the charge of the
metallic coatings or balls.

1237. To examine this state more accurately, the apparatus, with the
hemispherical cup of shell-lac in it, was charged for about forty-five
minutes to above 600 deg. with positive electricity at the balls _h_ and B.
(fig. 104.) above and within. It was then discharged, opened, the shell-lac
taken out, and its state examined; this was done by bringing the carrier
ball near the shell-lac, uninsulating it, insulating it, and then observing
what charge it had acquired. As it would be a charge by induction, the
state of the ball would indicate the opposite state of electricity in that
surface of the shell-lac which had produced it. At first the lac appeared
quite free from any charge; but gradually its two surfaces assumed opposite
states of electricity, the concave surface, which had been next the inner
and positive ball; assuming a positive state, and the convex surface, which
had been in contact with the negative coating, acquiring a negative state;
these states gradually increased in intensity for some time.

1238. As the return action was evidently greatest instantly after the
discharge, I again put the apparatus together, and charged it for fifteen
minutes as before, the inner ball positively. I then discharged it,
instantly removing the upper hemisphere with the interior ball, and,
leaving the shell-lac cup in the lower uninsulated hemisphere, examined its
inner surface by the carrier ball as before (1237.). In this way I found
the surface of the shell-lac actually _negative_, or in the reverse state
to the ball which had been in it; this state quickly disappeared, and was
succeeded by a posi