the boy or was the father right? If the father was right,
should they have got a fuse marked _6A_, one marked _10A_, or
one marked _15A_?

_APPLICATION 61._ The family were putting up an extension
light. They wanted the cord held firmly up out of the way.
One suggested that they drive a nail through both parts of the
cord and into the wall. Another thought it would be better to
put a loop of string around the cord and fasten the loop to
the wall. A third suggested the use of a double-pointed carpet
tack that would go across the wires, but not through them,
and if driven tightly into the wall would hold the wire more
firmly than would the loop.

Which way was best?

INFERENCE EXERCISE

Explain the following:

361. If the insulation wears off both wires of a lamp cord,
the fuse will blow out.

362. Street cars are heated by electricity.

363. The handles of pancake turners are often made of wood.

364. Glue soaks into the pores of pieces of wood and gradually
hardens.

365. The glue then holds the pieces tightly together.

366. You need a fuse of higher amperage, as a 10-ampere fuse,
instead of a 6-ampere one, where you use electricity for an
iron, and one of still higher amperage for an electric stove.

367. You should be careful about turning on electric lights or
doing anything with electric wires when you are on a cement,
iron, or earthen floor, or if you are standing in water.

368. The keys and buttons with which you turn on electric
lights are usually made of a rubber composition.

369. Defective wiring, because of which bare wires may touch,
has caused many fires.

370. A person wearing glasses can sometimes see in them the
image of a person behind him.

SECTION 40. _Electromagnets._

How is a telegram sent?

What carries your voice when you telephone?

So far we have talked about electricity only making heat and light by
being forced through something that resists it. But everybody knows
that electricity can be made to do another kind of work. It can
be made to move things,--to run street cars, to click telegraph
instruments, to vibrate the thin metal disk in a telephone receiver,
and so on. The following experiments will show you how electricity
moves things:

[Illustration: FIG. 138. The magnetized bolt picks up the iron
filings.]

EXPERIME