I
obtained the return charge, but only to an amount of 17 deg. or 18 deg.. Thus glass
and sulphur, which are bodily very bad conductors of electricity, and
indeed almost perfect insulators, gave very little of this return charge.

1243. I tried the same experiment having _air_ only in the inductive
apparatus. After a continued high charge for some time I could obtain a
little effect of return action, but it was ultimately traced to the
shell-lac of the stem.

1244. I sought to produce something like this state with one electric power
and without induction; for upon the theory of an electric fluid or fluids,
that did not seem impossible, and then I should have obtained an absolute
charge (1169. 1177.), or something equivalent to it. In this I could not
succeed. I excited the outside of a cylinder of shell-lac very highly for
some time, and then quickly discharging it (1203.), waited and watched
whether any return charge would appear, but such was not the case. This is
another fact in favour of the inseparability of the two electric forces
(1177.), and another argument for the view that induction and its
concomitant phenomena depend upon a polarity of the particles of matter.

1245. Although inclined at first to refer these effects to a peculiar
masked condition of a certain portion of the forces, I think I have since
correctly traced them to known principles of electrical action. The effects
appear to be due to an actual penetration of the charge to some distance
within the electric, at each of its two surfaces, by what we call
_conduction_; so that, to use the ordinary phrase, the electric forces
sustaining the induction are not upon the metallic surfaces only, but upon
and within the dielectric also, extending to a greater or smaller depth
from the metal linings. Let _c_ (fig. 113.) be the section of a plate of
any dielectric, _a_ and _b_ being the metallic coatings; let _b_ be
uninsulated, and _a_ be charged positively; after ten or fifteen minutes,
if _a_ and _b_ be discharged, insulated, and immediately examined, no
electricity will appear in them; but in a short time, upon a second
examination, they will appear charged in the same way, though not to the
same degree, as they were at first. Now suppose that a portion of the
positive force has, under the coercing influence of all the forces
concerned, penetrated the dielectric and taken up its place at the line
_p_, a corresponding portion of the negative force havin