single wire could be made
to carry into a building the current for electric lights. This is
because the ground can carry electricity.

If you make all connections from a battery or dynamo just as for any
complete circuit, but use the earth for one wire, the electricity will
flow perfectly well (Fig. 127). To connect an electric wire with the
earth, the wire must go down deep into the ground and be well packed
with earth; but since water pipes go down deep and the earth is
already packed around them, the most convenient way to ground a
circuit is to connect the wire that should go into the ground with the
water pipe. The next experiment, the grounding of a circuit, should be
done by the class with the help of the teacher.

[Illustration: FIG. 127. The ground can be used in place of a wire to
complete the circuit.]

EXPERIMENT 68. _Caution: Keep the switches turned off throughout this
experiment._[6]

[Footnote 6: All through this chapter it is assumed that the
electrical apparatus described in the appendix is being used. In this
apparatus all the switches are on one wire, the other wire being alive
even when the switches are turned off.]

(a) Put a piece of fuse wire across the fuse gap. Screw the
plug with nails in it into the lamp socket. Connect the bare
end of a piece of insulated wire to the water faucet and touch
the other end to one nail of the plug. If nothing happens,
touch it to the other nail instead. The electricity has gone
down into the ground through the water pipe, instead of into
the other wire. The ground carries the electricity back to the
dynamo just as a wire would.

(b) Put a new piece of fuse wire across the gap. _Keep
switches turned off._ Touch the brass disk at the bottom of
an electric lamp to the nail which worked, and touch the wire
from the faucet to the other brass part of the lamp (Fig.
129). What happens?

_Caution: Under no circumstances allow the switch to be turned
on while you are doing any part of this experiment. Under no
circumstances touch the wire from the faucet to the binding
posts of the fuse gap. Do only as directed._ Explain what
would happen if you disobeyed these rules.

[Illustration: FIG. 128. Grounding the circuit. The faucet and water
pipe lead the electricity to the ground.]

WHY A BIRD IS NOT ELECTROCUTED WHEN IT SITS ON A LIVE WIRE. If a man
accidentally touches a live wire that ca