Refer to figures.
Properties of a Magnet

A few thousand years ago it was discovered that certain materials could attract small pieces of iron and also, if freely suspended, would rotate until they were pointing approximately North - South. More recently it was discovered ferrous materials could be given these 'magnetic' qualities and bars of this material are called magnets.

Magnets emit a magnetic field and these lines of force converge near the ends of the magnet which are called poles. Irrespective of the shape of a magnet it will always have two poles. If a bar magnet is freely suspended it will align itself in a N/S direction, the end pointing north is called the north seeking or red pole the other end being the south seeking or blue pole. The magnetic lines of force eminate from the red pole and re enter the magnet at the blue pole.

The poles of two magnets can attract or repel each other depending on their orientation, the rule being:

• Like poles repel
• Unlike poles attract

The magnetised needle of a compass follows these rules.

Earths Magnetic field

The molten core of the rotating Earth generates a magnetic field which behaves in a similar manner to that of a bar magnet. Therefore the Earth has two magnetic poles, one in the northern hemisphere and one in the southern, incoveniently these don't coincide with the Earths geographical north and south poles. Because of the molten nature of the Earths core these poles wander by a few miles every year but are defined by a geographical position and named according to their location.

The magnetic pole which is currently situated in the Arctic between Canada and Siberia is called the North Magnetic Pole. The magnetic pole situated in the Antarctic is called the South Magnetic Pole. It's important to realise that these poles are named because of their geographical position on the Earth and not because of their magnetic polarities!

A magnetised compass needles north pole (north seeking) follows the rule that 'unlike poles attract' which indicates the the polarity of the Earths north magnetic pole is actually south. That's fair enough if you want to explain magnetic theory but in navigation terms the name of the magnetic pole that's in the northern hemishere,not far from the geographic North Pole, can't logically be called anything other than the North Magnetic Pole.

Therefore it's true to say that a compass placed anywhere on Earth will turn so that the north pole of the magnet inside the compass points towards the north magnetic pole.