er together, it
will be found that more current will now flow into each of them,
although the difference of potential between the two plates must
obviously remain the same, since each of them is still connected to
the battery.

[Illustration: Fig. 119. Condenser Plate]

Theory. Due to the proximity of the plates, the positive electricity
on plate _A_ is drawn by the negative charge on plate _B_ towards
plate _B_, and likewise the negative electricity on plate _B_ is drawn
to the side towards plate _A_ by the positive charge on that plate.
These two charges so drawn towards each other will, so to speak, bind
each other, and they are referred to as _bound charges_. The charge on
the right-hand side of plate _A_ and on the left-hand side of plate
_B_ will, however, be free charges, since there is nothing to attract
them, and these are, therefore, neutralized by a further flow of
electricity from the battery to the plate.

[Illustration: Fig. 120. Theory of Condenser]

Obviously, the closer together the plates are the stronger will be the
attractive influence of the two charges on each other. From this it
follows that in the case of plate _A_, when the two plates are being
moved closer together, more positive electricity will flow into plate
_A_ to neutralize the increasing free negative charges on the
right-hand side of the plate. As the plates are moved closer together
still, a new distribution of charges will take place, resulting in
more positive electricity flowing into plate _A_ and more negative
electricity flowing into plate _B_. The closer proximity of the
plates, therefore, increases the capacity of the plates for holding
charges, due to the increased inductive action across the dielectric
separating the plates.

Condenser Defined. A condenser is a device consisting of two
adjacent plates of conducting material, separated by an insulating
material, called a _dielectric_. The purpose is to increase by the
proximity of the plates, each to the other, the amount of electricity
which each plate will receive and hold when subjected to a given
potential.

Dielectric. We have already seen that the capacity of a condenser
depends upon the area of its plates, and also upon their distance
apart. There is still another factor on which the capacity of a
condenser depends, _i.e._, on the character of the insulating medium
separating its plates. The inductive action which takes place between
a charged conductor and othe