her."

"What I cannot understand is why the magnetic poles should be at the
north pole and at the south pole."

"The magnetic poles are not at the poles of the rotation of the earth,
but hundreds of miles away, to one side of the poles on which the earth
rotates; but they are near enough to the real poles, for all purposes,
so that the needle points to what we call the north pole of the earth.
Any magnetized body must have these two opposite poles. If it is a body,
like a bar of iron, one end is called north and the other south. Look at
this other sketch (Fig. 18) and you will see how the currents flow in
the two magnets. In this case the large body (E) represents the earth
and the small body (M) the magnet. Now notice that the current going
around the large body moves to the right, or to the north pole, whereas
the current in the small magnet (M) flows in the opposite direction."

[Illustration: _Fig. 18. MAGNETIC INDUCTION_]

"And does the current flowing around the bars, as you have shown, make
the small magnet turn around so that it is always parallel with the
large magnet, and make the north pole of one magnet at the same end with
the south pole of the other magnet?"

"Yes; to make it still clearer, I make two more drawings (Figs. 19 and
19a), in which two sets of magnets are shown. In the first of these
pairs of magnets (Fig. 19), the two north poles approach each other, and
the two south poles are opposite each other. The currents, if you will
notice, at the north poles move toward each other, and at the south
poles move away from each other. They are, therefore, acting against
each other, and the result will be that the magnets will move away from
each other. If, now, one of the magnets is turned so the poles of one
magnet approach the opposite poles of the other magnet, as shown in the
second view (Fig. 19a), they will attract each other, because the
current is permitted to flow through the two magnets in the same
direction without one conflicting with the other."

[Illustration: _Fig. 19. Fig. 19a. THE TWO MAGNETS_]

"Is that the reason it is stated that likes repel and unlikes attract?"

"Yes."

In order to take advantage of this knowledge, knowing that the earth is
a great permanent magnet, it was necessary to make a small magnet, and
so suspend it that it would turn freely, and the magnetic north and
south could then be determined.

To do this the battery which had been previously made was brough