Squirrel fan mail: How to build a homemade compass

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CompassDear Kelly,

I heard you on the radio saying that you like to take a compass reading of the emergency staircase when you go into multi-storey building so that you would know how to get out if the air was filled with smoke or the building had lost its landmarks.

It made me wonder if you know how to make a compass from a needle or a razor blade.  (The answer to that is definitely no! But I want to. Tell me more – Kelly.) In fact, you can make one from any piece of ferrous metal (metal with iron in it, e.g. steel) like needles, a nail or an old-fashioned double-edged razor blade. You’ll also need a piece of string, hair or leather to hang it on. Don’t use anything with metal in it, as it’ll mess with the magnetic field.

Magnetise (polarize) the metal by slowly rubbing it in one direction on a piece of silk or stroke it on your hair using slow strokes, like you do when you make static electricity by rubbing a balloon on your hair or sweater. You can also make it magnetic by rubbing one end over and over with a magnet. Rub in one direction only, don’t go back and forth. This will lie north-south.

If you have a 9-volt battery and some electric wire, you can make a basic electromagnet. Strip the two ends of the wire so there’s some bare metal showing. Twist the electric wire into a coil and connect the ends to the terminals. Repeatedly insert one end of your metal object (needle, small nail, etc.) in and out of the coil. It will become an electromagnet. If you hang it from a cord or float it on piece of cork or a sliver of wood in water, it will lie along the north-south axis.

I used these methods to teach my boys about magnets but I guess they have survival uses too.

Cleo Hawkins, Winchester, VA

We found this on YouTube which makes the point.