were named lodestones, from the word "lode," meaning a way or path, that which leads.

We can magnetize a piece of steel, such as a knife blade or a needle, by stroking it against one of these lodestones, just as well as against a bar or horseshoe magnet.

N

S

Who do you suppose it was that first suspended a magnet or lodestone (Fig. 127), so that it could swing around to take any position it chose? Perhaps he placed it upon a floating chip or plank, and was astonished to see the floating body hair or by untwisted silk, turn about until the magnet was lying in a general north and south

FIG. 127. If a bar magnet is suspended by a

it will be free to turn to the N-S position.

direction. Whoever he was, this man (or was it a woman?) of long ago had discovered the principle of the

FIG. 128. — If a needle is floated upon water in a glass or porcelain dish, and is then magnetized, it turns until it has a N-S position.

compass. The compass was

in use long before the time of Columbus.

You can make a compass for yourself. Push a sewing or darning needle through a slice of a small cork (Fig. 128), and float the cork and needle upon water in a glass or porcelain dish (not an iron one). Does the floating body seem to prefer to lie in any particular direction? Now magnetize the needle, and float it upon the water; what happens?

When you face north, which of your hands points east? Which west? What gain was it for sailors to be able to tell which direction was north? How did it affect the length of their voyages and their going out of sight of land? How, then, did it affect civilization?

216. What are the Poles of a Magnet? - Magnetize a steel knitting needle, then lay it on a sheet of paper and sprinkle iron filings over it. What happens when you lift the needle out of the filings? To what parts of the magnetized needle do the filings cling?

Make a deep file mark at the middle of your knittingneedle magnet and break the needle into two pieces; now put each of the pieces into the iron filings. What happens? Do not the two ends of each half pick up the bits of iron? See Fig. 129. If the steel needle were broken into four, or six, or any number of pieces, each piece would be a magnet. In each case the ends would attract the filings, but the middle would not. We call

FIG. 129. If a magnetized needle is broken into pieces, each piece is a magnet.

the two ends of a magnet its poles. The pole that would point to the north if the magnet were suspended, as in the compass, is called the north-seeking, or simply, the north pole, of the magnet; the other is called the southseeking, or simply, the south pole, of the magnet.

Bring an unmagnetized knitting needle or knife blade near the north pole of the floating compass which you have made (Fig. 128). Is one pole attracted as much as the other? Is either pole repelled? Then find (how?)

which is the north pole of one of your knitting-needle magnets, and bring this pole carefully near the north pole of your floating compass. What happens? Bring the south pole of your knittingneedle magnet near the south pole of your floating compass. What is the result? Finally hold the north pole of one near the south pole of the other and see what happens. What is the story told by Fig. 130?

S

FIG. 130.

N

N

S

One of the bar magnets is suspended, and the other bar magnet is brought near it. What happens?

Is this statement true: "In the case of two magnets, the two like poles repel each other, but the two unlike poles attract each other"?

Is it true that

217. What is a Temporary Magnet? once a magnet always a magnet"? With a bar magnet or horseshoe magnet hold a soft-iron bolt or wire, and then let the bar or wire touch a heap of tacks or brads. See how many tacks or brads your magnet will hold. (Look back at Fig. 124.) Here the soft-iron bar or wire

acts as a magnet and holds the other iron objects. Remove the magnet from the bar or wire; what happens? The soft iron does not retain its magnetic power, and so cannot hold the other objects. Since the soft iron will not hold its magnetism when left to itself, we call it a temporary magnet, that is, a magnet for the time being only. The steel of a real, or permanent, magnet keeps its magnetism for a long time unless it is heated; in that case it also loses its magnetism rapidly.

218. What is a Magnetic Field? You have already seen what happens if you bring a magnet up to the side of a compass: one end of the compass needle turns toward

FIG. 131. If a magnet is placed under a pane of glass, or a sheet of paper, the magnet's influence passes through, and each of the bits of iron on top of the pane or paper becomes a magnet.

the magnet, although the two do not touch each other. Try it again. Also try holding the magnet just above the compass; then below it. The results are the same: wherever you place the magnet, it will affect the compass needle, if the two are not too far apart.

Also carry out this experiment: Put a magnet under a plate of glass (Fig. 131); then sprinkle iron filings upon the glass, and tap it gently. The filings arrange themselves end to end in distinct curves. Why do they do this?

The region around a magnet is under the magnet's influence, or power, and every magnetic thing in this region is affected, whether it be another magnet, such as a compass needle, or a piece of steel, or iron filings. This influence extends in all directions, but its effects become less and less as we hold the objects farther and farther from the magnet. The space surrounding a magnet is called the magnet's "field," or a magnetic field.

219. Is the Earth a Magnet? We say that a compass points north and south, but this is true only in a general way. The place in the north to which our compass points is not the geographical north pole of the earth, but a magnetic pole located in Northern Canada, inside the Arctic Circle. In 1905 it was in latitude 70° 5' N. and longitude 96° 46′ W. Find it on a map. Even in the days of Columbus, men in Europe knew that the compass did not point exactly north. As Columbus sailed westward, he discovered another thing: the direction of the needle changes as we go from one place to another. This greatly frightened his sailors, for they thought they were going into regions from which they could never find their way back to their home.

Fig. 132 shows in a general way how far the compass direction is from the true north for different parts of America. In regions in which there are deposits of iron ore, as in Alabama and Michigan, the compass needle is drawn aside in an irregular way. The lines in the