rries a strong current of
electricity he is electrocuted; yet birds perch on such a wire in
perfect safety. If a man should leap into the air and grasp a live
wire, hanging from it without touching the ground, he would be no more
hurt by it than a bird is. A person who is electrocuted by touching
such a wire must at the same time be standing on the ground or on
something connected with it. The ground completes the electric circuit
which passes through the body. An electric circuit can always be
completed through the ground, and when this is done, it is called
_grounding a circuit_.

[Illustration: FIG. 129. How the lamp and wire are held to ground the
circuit.]

_APPLICATION 54._ Explain why only one wire is needed to
telegraph between two stations; why you should not turn an
electric light on or off while standing in a tub of water.

_APPLICATION 55._ In a house in the country, the electric wires
passed through a double wall. They were separated from each
other and well covered with insulation, but they were not
within an iron pipe, as is now required in many cities. The
current was alternating. One night when the lights were out a
rat in the wall gnawed through the insulation of the wire
and also gnawed clear through one of the wires. Did he get a
shock? The next morning, the woman of the house wanted to use
the electric iron in the kitchen and it would not work. The
kitchen had in it a gas stove, a sink with running water, a
table, a couple of chairs, and the usual kitchen utensils.
There was also a piece of wire about long enough to reach
across the kitchen. The electrician could not come out for
several hours, and the woman wanted very much to do her
ironing. Figure 130 is a diagram of the wires and the kitchen.
Show what the woman might have done in order to use her iron
until the electrician arrived.

[Illustration: FIG. 130. How can the electric iron be used after one
wire has been cut?]

_APPLICATION 56._ A man wanted to change the location of the
wiring in his cement-floored garage. While he was working,
would it have been best for him to stand on the bare cement
floor, on a wire mat, on an old automobile tire, on a wet rug,
or on some skid chains that were there?

INFERENCE EXERCISE

Explain the following:

331. An ungreased wheel squeaks.

332. Lightning rods extend into the earth.