[Illustration: FIG. 1.]
This mysterious "agent," as people call it for want of a better word,
can be produced in the easiest fashion, and some of its ways studied
with the simplest kind of apparatus, constructed of articles that lie
close at hand.
If we rub a stick of sealing-wax with a piece of cloth, we shall see
that it will attract some small fragments of paper placed near it.
Nothing is easier than to construct a small pendulum to show with
perfect clearness the wonder of electric attraction. A piece of iron is
fixed on a wooden pedestal, and holds a thread of silk, to the end of
which is fastened a little ball cut out of a piece of cork. The stick of
sealing-wax, after being rubbed with the cloth, will attract the ball,
as shown in Fig. 1.
[Illustration: FIG. 2.]
We can easily construct other electrical apparatus. Take a lacquered
tea-tray about a foot long, and cut out a sheet of thick wrapping paper
so that it will lie over all the level portion of the tray. At each side
of this sheet of paper fix two bands of paper, as in Fig. 2, so as to
serve as handles. The tea-tray should be placed upon two tumblers to
support it and to insulate it, glass being a "non-conductor." By a
non-conductor is meant a substance that will not convey electricity, or
allow it to pass away.
Now rub the thick packing-paper over a hot fire or a stove until it is
thoroughly dry, and as hot as possible without charring. When this has
been done, place it quickly upon a wooden table, and rub it rapidly with
as dry and hard a clothes-brush as can be obtained. Place the paper upon
the tray; touch the tray with the knuckle, and draw away the paper by
the handles fixed to it (see Fig. 2); a spark will result. Then if the
paper be replaced upon the tray, and the hand again presented, the same
result will follow. This may be done five or six times, at least, with
success.
[Illustration: FIG. 3.]
We have in this tea-tray and its paper covering a real electric machine.
How can we manage to provide a Leyden-jar (so named from its inventor,
Muschenbrock, of Leyden) to contain our electricity? Nothing is more
easy. Let us take a tumbler, and partly fill it with shot; insert into
the glass a tea-spoon, and if all the articles are quite dry, we shall
possess a Leyden-jar.
To charge the jar we must work our other machine. While one person lifts
off the paper as directed, another must hold the glass to the edge of
the tray, and touch the corner with the tea-spoon; the spark will then
enter the "jar." We can thus charge the jar as we please, and by
presenting the finger, as in Fig. 3, we shall obtain a discharge from
it.
[Illustration: FUN ON THE ICE--"KEEPING THE POT BOILING."]