Since magnets attract iron, can they attract other metals? Our ancestors made many attempts and found that magnets can not only attract metals such as gold, silver, and copper, but also can not attract bricks and tiles and the like. At the time of the Western Han Dynasty, people had realized that magnets only attracted iron and could not attract other objects. When two magnets are placed close together, they sometimes attract each other and sometimes they are mutually exclusive. It is known that magnets have two poles, one called the N pole and one called the S pole. The same sex is extremely exclusive and the opposite sex attracts each other. People at that time did not know this truth, but they could still be aware of this phenomenon.
In the Western Han Dynasty, there was an alchemist named Yan Da. He used the nature of magnets to make two pieces of chess. By adjusting the mutual position of the two chess pieces, sometimes the two pieces attracted each other and sometimes they were mutually exclusive. The big name is "battle." He dedicated this novelty to Han Wudi and demonstrated on the spot. Han Wudi was amazed and the Dragonheart was greatly pleased, and he was actually called “General Wu Li”. Zheda made use of the nature of the magnets to create novelties and deceived Han Wudi.
The Earth is also a large magnet. Its two poles are close to the geographic South Pole and the geographical North Pole. Therefore, when the magnets on the surface of the earth can rotate freely, they will be repelled because of the homogeneity of the magnets, and the properties of the opposite sex attraction indicate north and south. This principle is not well understood by the ancients, but they are very clear about this phenomenon.