nd around to the south; let go and watch it.
Place the magnet the other way around in the loop so that you
can be sure that it is not twisting of the shoestring that
makes the magnet turn in this direction.

Now stroke a needle several times along one arm of the magnet,
_always in the same direction_, as shown in Figure 105. Hold
the needle over some iron filings or touch any bit of iron
or steel with it. What has the needle become? Lay it on a
cardboard milk-bottle top of the flat kind, and on that float
it in the middle of a glass or earthenware dish of water.
Notice which end turns north. Turn this end to the south and
see what happens. Hold your magnet, ends up, under the dish,
and turn the magnet. What does the needle do?

[Illustration: FIG. 104. The compass needle follows the
magnet.]

Now it should be easy to understand why the compass points north. One
end of any magnet pulls on _one_ end of another magnet and drives the
_other_ end away. The earth is a big magnet. So if you make a magnet
and balance it in such a way that it is free to swing, the north end
of the big earth magnet pulls one end of the little magnet toward
it and pushes the other end away. Therefore one end of your compass
always points north.

OTHER EFFECTS OF THE EARTH'S MAGNETISM. Another interesting effect
of the earth's being a big magnet is to be seen if you lay a piece of
steel so that it points north and south, and then pound it on one end.
It becomes magnetized just as your needle became magnetized when it
was rubbed on the small magnet.

[Illustration: FIG. 105. Magnetizing a needle.]

[Illustration: FIG. 106. A compass made of a needle and a piece of
cardboard.]

And still another effect of the earth's magnetism is this: Tiny
particles of electricity, called _electrons_, are probably shooting
through space from the sun. It is believed that as they come near the
earth, the magnetism of the north and south polar regions attracts
them toward the poles, and that as they rush through the thin, dry
upper air, they make it glow. And this is probably what causes the
Northern Lights or Aurora Borealis.

WHAT HAPPENS WHEN A NEEDLE IS MAGNETIZED. The reason that a needle
becomes magnetic if it is rubbed over a magnet is probably this:
Every molecule of iron may be an extremely tiny magnet; if it is, each
molecule has a north and south pole like the needle of a compass. In
an ordinary nee