on
fire by short circuits as by arcs. Perhaps there would be more danger,
because short circuits are the more common.

EXPERIMENT 73. Put a new piece of fuse wire across the fuse
gap. Leave the "nail plug" screwed in the socket. Use a piece
of flexible lamp cord--the kind that is made of two strands of
wire twisted together (see Fig. 137). Fasten one bared end of
each wire around each nail of the "nail plug." See that the
other ends of the lamp cord are not touching each other.
Turn on the electricity. Does anything happen? Turn off the
electricity. Now put a pin straight through the middle of the
two wires. Turn on the electricity again. What happens?

There is not much resistance in the pin, and so it allows the
electricity to rush through it. People sometimes cause fuses to blow
out by pinning pictures to electric lamp wires or by pinning the wires
up out of the way.

A SHORT CIRCUIT AN "EASY CIRCUIT." You always get a short circuit when
you give electricity an easy way to get from one wire to the other.
But you get no current unless you give it some way to pass from one
wire to the other, thus completing the circuit. Therefore you should
always complete the circuit through something which resists the flow
of electricity, like an electric lamp, a heater, or an iron. Remember
this and you will have the key to an understanding of the practical
use of electricity.

The term "short circuit" is a little confusing, in that electricity
may have to go a longer way to be short circuited than to pass through
some resistance, such as a lamp. Really a short circuit should be
called an "easy circuit" or something like that, to indicate that it
is the path of least resistance. Wherever the electricity has a
chance to complete its circuit without going through any considerable
resistance, no matter how _far_ it goes, we have a short circuit. And
since everything resists electricity a little, a large enough flow
of electricity would even heat a _copper_ wire red hot; that is why a
short circuit would be dangerous if you had no fuses.

_APPLICATION 59._ To test your knowledge of short circuits and
fuses, trace the current carefully from the upper wire as it
enters the laboratory, through the plug fuse. Show where it
comes from to enter the plug fuse, exactly how it goes through
the fuse, where it comes out, and where it goes from there.
Trace it on through the cartri