指南针是我国古代的四大发明之一。早在公元前人们就利用指南针在行军和航海中辨别方向。指南针之所以总是停留在南北方向上,是因为地球上存在支配磁针指向的神秘力量——地球本身就是一块大磁石。科学家发现,地球上磁性最强的地方是磁北极和磁南极,磁性最弱的地方是磁赤道。地磁南北极与地理两极不重合,偏离一个角度——磁偏角,大约11°,如图1。目前,磁北极位于北半球 Compass is one of the four great inventions in ancient China. As early as BC, people used compass to discern directions in march and sailing. The reason why the compass always stays in the north-south direction is because of the mysterious force that dominates the needle pointing on Earth - the earth itself is a big magnet. Scientists found that the most magnetic places on the earth are the magnetic north pole and the magnetic south pole, and the weakest magnetic field is the magnetic equator. Geomagnetic polar north and south poles do not coincide, deviate from an angle - declination, about 11 °, as shown in Figure 1. At present, the magnetic north is located in the northern hemisphere