g also assumed its
position at the line _n_; that in fact the electric at these two parts has
become charged positive and negative; then it is clear that the induction
of these two forces will be much greater one towards the other, and less in
an external direction, now that they are at the small distance _np_ from
each other, than when they were at the larger interval _ab_. Then let _a_
and _b_ be discharged; the discharge destroys or neutralizes all external
induction, and the coatings are therefore found by the carrier ball
unelectrified; but it also removes almost the whole of the forces by which
the electric charge was driven into the dielectric, and though probably a
part of that charge goes forward in its passage and terminates in what we
call discharge, the greater portion returns on its course to the surfaces
of _c_, and consequently to the conductors _a_ and _b_, and constitutes the
recharge observed.

1246. The following is the experiment on which I rest for the truth of this
view. Two plates of spermaceti, _d_ and, _f_ (fig. 114.), were put together
to form the dielectric, _a_ and _b_ being the metallic coatings of this
compound plate, as before. The system was charged, then discharged,
insulated, examined, and found to give no indications of electricity to the
carrier ball. The plates _d_ and _f_were then separated from each other,
and instantly _a_ with _d_ was found in a positive state, and _b_ with _f_
in a negative state, nearly all the electricity being in the linings _a_
and _b_. Hence it is clear that, of the forces sought for, the positive was
in one-half of the compound plate and the negative in the other half; for
when removed bodily with the plates from each other's inductive influence,
they appeared in separate places, and resumed of necessity their power of
acting by induction on the electricity of surrounding bodies. Had the
effect depended upon a peculiar relation of the contiguous particles of
matter only, then each half-plate, _d_ and _f_, should have shown positive
force on one surface and negative on the other.

1247. Thus it would appear that the best solid insulators, such as
shell-lac, glass, and sulphur, have conductive properties to such an
extent, that electricity can penetrate them bodily, though always subject
to the overruling condition of induction (1178.). As to the depth to which
the forces penetrate in this form of charge of the particles,
theoretically, it should be througho