Fill a plastic bowl half full of water and place it on a level surface. Do not use a metal bowl; metal will interfere with your results. If you place the bowl on a table, use a wooden or plastic table rather than metal.
Cut a bottle cork so that you have a piece of cork with a width greater than its height. Set aside the remainder of the cork.
Place a magnet against the center of a large sewing needle. Stroke the magnet toward the tip of the needle. Stroke away from yourself to avoid injury. Repeatedly stroking the magnet on the needle in the same direction, between 20 and 50 times; this will magnetize the needle's tip.
Tape the needle to the top of the cork piece with a small piece of clear tape. Center the needle as evenly as possible.
Place the cork in the center of the bowl of water so that the needle rests on top of the cork.
Spin the cork gently so that the cork and needle rotate slowly. Wait for the cork to stop rotating and note the direction toward which the pointed tip of the needle faces. It will be pointing north.
Use a marker to mark north, south, east and west on the plastic bowl. North is where the pointed tip of the needle faces; south is the point opposite north; east is right of of the north and south points, equally between them; and west is the point opposite east.