Robert,

I already learned something today.

An interesting detail is that there are northern-hemisphere and southern-hemisphere compasses. This is due to the fact that the magnetic field lines to which a compass needle aligns point into the earth at the north and south magnetic poles. This means that in the northern hemisphere, the north end of the needle is pulled downwards and so the south end is counter-weighted to balance the needle. Therefore, when you use a northern hemisphere compass in, say Australia, the south end of the magnet is pulled downwards by the magnetic field and is also heavier than the north end - resulting in a needle that catches and drags on the bottom of the compass housing when the compass is held horizontal.

johninbastrop

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