ctricity goes through your body, you get a shock. The shock from
the ordinary current of electricity, 110 volts, is not enough to
injure you at all; in fact, if you were standing on dry wood, it would
be _safe_, although you would get a slight shock, to connect the blade
of a knife switch to the slot of the switch, through your hand or
body. Your body would not allow enough current to pass through it to
light the lamp. Stronger currents, like those of power lines and even
trolley wires, are extremely dangerous.

All the electric wires entering your house are made of copper. They
are all covered with cloth and rubber and are fastened with glass
or porcelain knobs. The reason is simple: Copper and practically all
other metals are very good conductors of electricity; that is, they
allow electricity to pass through them very easily. Cloth, rubber,
glass, and porcelain are very poor conductors, and they are therefore
used as insulators,--to keep the electricity from going where you do
not want it to go.

[Illustration: FIG. 120. Will electricity go through the glass?]

EXPERIMENT 66. To each binding post of an electric bell fasten
a piece of insulated copper wire with bare ends and at least 4
feet long. Connect the free end of one of these wires with one
pole of a battery, using a regular laboratory battery or one
you made yourself. Attach one end of another piece of wire
a foot or so long, with bare ends, to the other pole of the
battery. Touch the free end of this short wire to the free end
of the long wire, as shown in Figure 120. Does the bell ring?
If it does not, something is wrong with the connection or with
the battery; fix them so that the bell will ring. Now leave a
gap of about an inch between the free end of the long wire
and the free end of the short wire. Try making the electricity
flow from the short wire into the long one through a number of
different things, such as string, a key, a knife, a piece of
glass tubing, wet cloth, dry cloth, rubber, paper, a nail,
a dish of mercury (dip the ends of the wire into the dish so
that they both touch the mercury at the same time), a dish of
water, a stone, a pail, a pin, and anything else that you may
like to try.

[Illustration: FIG. 121. Electrical apparatus: _A_, plug fuse; _B_,
cartridge fuse; _C_, knife switch; _D_, snap switch; _E_, socket with
nail plug in it; _F_, fuse gap; _G_, flu