What was the working principle of Sina in ancient China?

The principle of 1 and Sina is the principle of compass positioning.

2, that is, the earth is a big magnet, with its geomagnetic south pole near the geographical north pole and the geomagnetic north pole near the geographical south pole. The needle of a compass is actually a needle magnet. Under the magnetic force of the earth's magnetic field, one end of the compass will be guided and the other end will point to the north. In ancient China, pointer instruments were made by using the north and south finger polarities of magnets. Sina consists of a smooth magnetic spoon and a copper plate engraved with directions. When in use, turn the spoon by hand. When the spoon stops, the handle of the spoon points south. In the long-term practice, the method of making compass with artificial magnet has been found, and the types of compass are becoming more and more diverse. China is the first country in the world to use a compass to navigate. At that time, the compass used by ships had developed into a shape similar to that of later generations.