Science corner

30th January 2004 at 00:00
Sophie Duncan gives directions for making your own compass

The magnetic compass was a Chinese invention dating from around 220bc. At first, the compass was made from lodestone, which, when suspended, aligns itself to the Earth's magnetic field.

It was the observations of fortune-tellers, who used lodestone in their work, that prompted the discovery that it could be used to determine North.

It was not until 1,000 years later that the lodestone was replaced by a magnetised needle.

It is easy to make a compass from some simple materials: a needle, a magnet (any - even a fridge magnet), a cork and a small container of water.

Cut a small slice off the cork. Alternatively, if you are making a number of compasses, buy a cork tile and cut it into small pieces. Hold the needle by one end and stroke it with the magnet 80 times - making sure that you only stroke the needle in one direction, not back and forth.

Now attach the needle to the cork disc and place it in the container of water. The container must be large enough not to affect the motion of the needle. The needle will align itself to the Earth's magnetic field, along the North-South axis. If you move the container, the needle will realign itself.

An even easier way to determine where North is takes slightly longer. Place a stick in the ground outside and mark the end of the shadow early morning and late afternoon. The first mark is West, and the second East. If you stand with your left foot on the first mark and your right foot on the second, you will be facing North.

Having made a compass, your students could use it to create a treasure map of your school grounds.

Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience

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