Lodestone

What you need

  • A small lodestone, also called magnetite (or use a bar magnet)
  • A bowl of water
  • A selection of plastic containers that can be used as floats
  • A pen to write on the plastic container
  • Glue, blutac or sticky tape to attach the lodestone to the float
  • A compass or a location where you can already know 'North'

What you do

  1. Choose your float… try different containers to put your lodestone in, and float it on the bowl of water.  If the lodestone persistently sinks, your plastic container is not big enough.  Once you have found one, stick your lodestone in place on the float.
  2. Place the lodestone and float carefully back in the bowl of water.  Try not to artificially spin it.  Let it come to a rest without touching the sides of the bowl.
  3. Either use your compass or your local knowledge to identify 'North' and mark this on the float.
  4. You are now ready to take your compass into the field.
  5. When you need to find a direction, place your lodestone and float in a bowl of water and wait for it to settle.  This should tell you where north is and you can work out the other directions from there!

What's going on

Modern compasses have a tiny magnet shaped like an arrow, which can spin freely in a case.  A magnet, usually made of iron, will have north pole and a south pole.  The entire Earth is also a magnet, an enormous one which also has a north and a south pole.  The north pole of the tiny compass magnet points to the Earth's north pole.  (Very annoyingly the Earth's north pole is actually a magnetic south pole, as unlike poles attract.)

The entire lodestone is a magnet too, again with a north pole and a south pole.  It is made of a mineral call magnetite.  It is considerably bigger and more cumbersome to use than a modern compass.  But its north pole will point to the Earth's north pole.  Once you have identified where the north pole of lodestone is it can be used anywhere to point north.