sh switch; _H_, lamp socket;
_I_, _J_, _K_, resistance wire.]

Each thing that makes the bell ring is a good conductor. Each one that
will not make it ring is a poor conductor or an insulator. Make a list
of the things you have tried; in one column note the good conductors,
and in another column note the insulators and poor conductors.

The water and wet cloth did not ring the bell, but this is because the
pressure or voltage of the electricity in the batteries is not very
high. In dealing with high-power wires it is much safer to consider
water, or anything wet, as a pretty good conductor of electricity.
Absolutely pure, distilled water is an extremely poor conductor; but
most water has enough minerals dissolved in it to make it conduct
electricity fairly well. In your list you had better put water and wet
things in the column with the good conductors.

_APPLICATION 50._ Robbers had cut the telegraph line between two
railroad stations (Fig. 122). The broken ends of the wire fell to
the ground, a number of feet apart. A farmer caught sight of the men
speeding away in an automobile and he saw the cut wires on the
ground. He guessed that they had some evil purpose and decided to
repair the damage. He could not bring the two ends of the wire
together. He ran to his barn and found the following things there:

A ball of cord, a pickax, a crowbar, some harness, a wooden wagon
tongue, a whip, a piece of iron wire around a bale of hay (the wire
was not long enough to stretch the whole distance between the two
ends of the telegraph wire, even if you think he might have used it
to patch the gap), a barrel with four iron hoops, and a rope.

Which of these things could he have made use of in connecting the
broken ends of the telegraph wire?

[Illustration: FIG. 122. Which should he choose to connect the broken
wires?]

_APPLICATION 51._ A man was about to put in a new socket for an
electric lamp in his home. He did not want to turn off the current
for the whole house, as it was night and there was no gas to furnish
light while he worked.

"I've heard that if you keep your hands wet while you work, the film
of water on them will keep you from getting a shock," his wife said.

"Don't you wet your hands, Father," said his 12-year-old boy; "keep
them dry, and handle the wires with your pliers, so that you won't
have to touch it."