for the steel of his knife is only efficacious when the blade
itself becomes magnetic after being touched with the magnet. A
piece of steel is readily magnetised by stroking it from end to
end in one direction with the pole of a magnet, and in this way
compass needles and powerful bar magnets can be made.

The poles attract iron at a distance by "induction," just as a
charge of electricity, be it positive or negative, will attract a
neutral pith ball; and Dr. Gilbert showed that a north pole always
repels another north pole and attracts a south pole, while, on the
other hand, a south pole always repels a south pole and attracts a
north pole. This can be proved by suspending a magnetic needle
like a pithball, and approaching another towards it, as
illustrated in figure 26, where the north pole N attracts the
south S. Obviously there are two opposite kinds of magnetic poles,
as of electricity, which always appear together, and like magnetic
poles repel, unlike magnetic poles attract each other.

It follows that the magnetic pole of the compass needle which
turns to the north must be unlike the north and like the south
magnetic pole of the earth. Instead of calling it the "north," it
would be less confusing to call it the "north-seeking" pole of the
needle.

Gilbert made a "terella," or miniature of the earth, as a magnet,
and not only demonstrated how the compass needle sets along the
lines joining the north and south magnetic poles, but explained
the variation and the dip. He imagined that the magnetic poles
coincided with the geographical poles, but, as a matter of fact,
they do not, and, moreover, they are slowly moving round the