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By the third
century AD, Chinese scientists had studied and learned much
about magnetism in nature. For example, they knew that iron
ore, called magnetite, tended to align itself in a
North/South position. Scientists learned to "make magnets"
by heating pieces of ore to red hot temperatures and then
cooling the pieces in a North/South position. The magnet was
then placed on a piece of reed and floated in a bowl of
water marked with directional bearings. These first
navigational compasses were widely used on Chinese ships by
the eleventh century AD.
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