Making a Magnetic Compass

With the materials found on most boats, it is possible to magnetise a needle and float it on a dish of water to discover magnetic north (see Figures 6.1 to 6.3.)

If you feel that one needle is not enough to swing the straw then use two or three needles. Be sure that all the north poles point in the same direction (see Figure 6.4).

A fair estimate of variation can be found by pointing the bows at Polaris and noting where the compass needle points, or by holding a thin wooden or plastic rod, thinner than a pencil, over the compass needle at local noon. The angle made by the shadow of the rod and the compass needle is, approximately, the magnetic variation.

Serial

Item

1

One needle, a very small nail, a straightened out paper clip or similar.

2

One magnet or a silk cloth. Magnets are found in stereo speakers.

3

One plastic bowl, traditionally round but any shape will do. A Tupperware type bowl is good, so is cutting out a plastic bottle to make a bowl. If a plastic bowl is not available use any small non-ferrous bowl.

4

Water or light oil.

5

Two tiny pieces of cork or a drinking straw or a couple of fragments of polystyrene foam. Tradition has it that in the early compasses the needle was pushed through a straw to form a cross.

6

Some cling film if you have it. This is to cover the bowl and stop the water or oil slopping about. If you have no cling film use water rather than oil.

6.1 Magnetic Compass Component List

Serial

Action

1

Hold the needle in one hand and the magnet in the other.

2

Put the north end of the needle in the middle of the magnet and draw it along the needle towards the point. If you do not know which end of the magnet is north then make a guess. See Figure 6.3

3

Repeat this about 20 or so times.

4

Turn the magnet over and draw from the middle of the needle towards the eye of the needle about 20 times.

5

If you have no magnet then rub the needle vigorously on a silk cloth or in your hair for a couple of minutes.

6

Using either method, by the time you have stopped rubbing you have magnetized the needle and it behaves just like a compass needle. The magnetism diminishes with time and you will need to stroke the needle every few days.

7

Stick a tiny piece of cork, polystyrene foam, straw, or anything light that floats on each end of the needle so it floats.

8

Fill the bowl with oil or water. Use seawater if water is scarce.

9

Place the needle on the water or oil in a small bowl.

10

Wrap a layer of cling film over the bowl to protect it from the wind. The water or oil acts as natural gimbals.

6.2 Making a Magnetic Compass

6.3 Magnetizing a Needle

6.4 A Homemade Magnetic Compass

To make a square of paper without any ruler; take a sheet of paper, fold one corner across, mark the surplus by folding that and then cutting if off. You have a square of paper.

To make a square of paper without any ruler; take a sheet of paper, fold one corner across, mark the surplus by folding that and then cutting if off. You have a square of paper.

6.5 Making a Paper Square

You can also check your compass error against an amplitude, (see Chapter 7). Minimise deviation by keeping your compass away from anything that may influence it.

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