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Had the ancients known the phenomenon clearly about magnets long before?
In XiHan Dynasty, people had recognized that the permanent magnets can only attract iron, but can not attract other items. When the two magnets are together close to each other, sometimes they attract with each other, and sometimes they mutually exclude with each other.
Now, people all know that permanent magnet has two poles: a N pole and a S pole. The same pole mutually excludes, and the opposite pole attracts with each other. At that time, people do not know this truth, but this phenomenon could be perceived.
The earth is also a big magnet field, and its two electrodes are respectively near the geographic South Pole and the geographic north. Therefore magnets on earth surface can rotate freely, and they direct to the North of the South, due to the nature of magnets. The ancients don't know this reason, but they know clearly this kind of phenomenon.
from：http://www.htmagnets.com/newsd-nid-6.html
