, I think,
the most important at present; for, if shown to take place in an
unexceptionable manner, I do not see how the old theory of action at a
distance and in straight lines can stand, or how the conclusion that
ordinary induction is an action of contiguous particles can be resisted.

1216. There are many forms of old experiments which might be quoted as
favourable to, and consistent with the view I have adopted. Such are most
cases of electro-chemical decomposition, electrical brushes, auras, sparks,
&c.; but as these might be considered equivocal evidence, inasmuch as they
include a current and discharge, (though they have long been to me
indications of prior molecular action (1230.)) I endeavoured to devise such
experiments for first proofs as should not include transfer, but relate
altogether to the pure simple inductive action of statical electricity.

1217. It was also of importance to make these experiments in the simplest
possible manner, using not more than one insulating medium or dielectric at
a time, lest differences of slow conduction should produce effects which
might erroneously be supposed to result from induction in curved lines. It
will be unnecessary to describe the steps of the investigation minutely; I
will at once proceed to the simplest mode of proving the facts, first in
air and then in other insulating media.

1218. A cylinder of solid shell-lac, 0.9 of an inch in diameter and seven
inches in length, was fixed upright in a wooden foot (fig. 106.): it was
made concave or cupped at its upper extremity so that a brass ball or other
small arrangement could stand upon it. The upper half of the stem having
been excited _negatively_ by friction with warm flannel, a brass ball, B, 1
inch in diameter, was placed on the top, and then the whole arrangement
examined by the carrier ball and Coulomb's electrometer (1180. &c.). For
this purpose the balls of the electrometer were charged _positively_ to
about 360 deg., and then the carrier being applied to various parts of the ball
B, the two were uninsulated whilst in contact or in position, then
insulated[A], separated, and the charge of the carrier examined as to its
nature and force. Its electricity was always positive, and its force at the
different positions _a, b, c, d,_ &c. (figs. 106. and 107.) observed in
succession, was as follows:

at _a_ above 1000 deg.
_b_ it was 149
_c_ 270
_d_ 512
_b