rther assumed, that these particles are polarized; that each exhibits the
two forces, or the force in two directions (1295. 1298.); and that they act
at a distance, only by acting on the _contiguous_ and intermediate
particles.

1616. But assuming that a perfect vacuum were to intervene in the course of
the lines of inductive action (1304.), it does not follow from this theory,
that the particles on opposite sides of such a vacuum could not act on each
other. Suppose it possible for a positively electrified particle to be in
the centre of a vacuum an inch in diameter, nothing in my present views
forbids that the particle should act at the distance of half an inch on all
the particles forming the inner superficies of the bounding sphere, and
with a force consistent with the well-known law of the squares of the
distance. But suppose the sphere of an inch were full of insulating matter,
the electrified particle would not then, according to my notion, act
directly on the distant particles, but on those in immediate association
with it, employing _all_ its power in polarizing them; producing in them
negative force equal in amount to its own positive force and directed
towards the latter, and positive force of equal amount directed outwards
and acting in the same manner upon the layer of particles next in
succession. So that ultimately, those particles in the surface of a sphere
of half an inch radius, which were acted on _directly_ when that sphere was
a vacuum, will now be acted on _indirectly_ as respects the central
particle or source of action, i.e. they will be polarized in the same way,
and with the same amount of force.

S 19. _Nature of the electric current._

1617. The word _current_ is so expressive in common language, that when
applied in the consideration of electrical phenomena we can hardly divest
it sufficiently of its meaning, or prevent our minds from being prejudiced
by it (283. 511.). I shall use it in its common electrical sense, namely,
to express generally a certain condition and relation of electrical forces
supposed to be in progression.

1618. A current is produced both by excitement and discharge; and
whatsoever the variation of the two general causes may be, the effect
remains the same. Thus excitement may occur in many ways, as by friction,
chemical action, influence of heat, change of condition, induction, &c.;
and discharge has the forms of conduction, electrolyzation, disruptive
discharg