The compass was first invented in Daming. Before the invention of the compass, people often lost their way in the vast sea, resulting in unimaginable consequences. It was China who invented the compass and pointed out the direction for human navigation. Compass is a simple tool to judge the direction. One of four great inventions of ancient china. The main component is a magnetic needle that can rotate freely on the shaft. The magnetic needle can be kept in the tangential direction of magnetic meridian under the action of geomagnetic field. The north pole of the magnetic needle points to the geographical south pole, which can be used to identify the direction. It is often used in navigation, geodesy, tourism and military affairs. The invention of compass is the result of our working people's understanding of the magnetism of objects in long-term practice. Due to productive labor, people came into contact with magnetite and began to understand its magnetism. People first discovered the property that magnets attract iron. Later, the directivity of magnets was discovered. After many experiments and studies, a practical compass was finally invented. The discovery of magnetic phenomena Our ancestors accumulated a lot of knowledge in this field in the pre-Qin period. When exploring iron ore, they often encounter magnetite, that is, magnetite (the main component is ferroferric oxide). These findings have long been recorded. These discoveries were first recorded in several articles in Guanzi: "There are magnets on the mountain and gold and copper under it." There are similar records in other ancient books, such as Shan Hai Jing. The iron-absorbing characteristics of magnets have long been discovered. The main chapter of the nine volumes of Lu's Spring and Autumn Annals is: "Kindly absorb iron, or absorb it." At that time, people called "magnetism" "kindness". They think that magnets attract iron is the attraction of loving mothers to their children. And think: "Stone is the mother of iron, but there are two kinds of stones: kind and unkind. Kindness can attract his children, but not kindness. " Before the Han Dynasty, people wrote magnets as "Guanyin Stone", which means love stone. Since magnets can 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 attract bricks and tiles. During the Western Han Dynasty, people realized that magnets could only attract iron, but not other objects. When two magnets are put together and close to each other, sometimes they attract each other and sometimes they repel each other. Now people all know that magnets have two poles, one is called N pole and the other is called S pole. Like-sex repulsion, opposites attract. People didn't know this truth at that time, but they could still perceive this phenomenon. In the Western Han Dynasty, there was an alchemist named Luan Da. He used this characteristic of magnet to make something similar to two chess pieces. By adjusting the mutual position of the polarities of two chess pieces, sometimes the two chess pieces attract each other and sometimes repel each other. Luan Da called it "playing chess". He dedicated the novel to Emperor Wu of the Han Dynasty and gave a live demonstration. Emperor Wu of the Han Dynasty was pleasantly surprised. He was named "General Five Blessingg". Luan made great use of the properties of magnets to make novel things to deceive Emperor Wu of Han Dynasty. The earth is also a big magnet, and its poles are close to the geographical south pole and the geographical north pole respectively. Therefore, when the magnets on the earth's surface can rotate freely, they will represent the north and south because of the nature that magnets repel each other with the same polarity and attract each other with the opposite polarity. The ancients did not understand this truth, but they knew this phenomenon very well. The ancestor of compass-the ancestor of Sina compass appeared in the Warring States Period. It is made of natural magnets. It looks like a spoon with a round bottom, which can be balanced on a smooth "field" and can rotate freely. When it is at rest, the handle of the spoon will point to the south. The ancients called it "Sina", and in the book Han Feizi at that time, there was: "Wang Li Sina took the time first." "Sooner or later" means square, east. Guiguzi recorded the application of Sina, and Zheng people took Sina with them when picking jade to make sure they didn't get lost. In the Spring and Autumn Period, nephrite and jadeite with hardness of 5-7 degrees can be polished into various shapes, so natural magnets with hardness of only 5.5-6.5 degrees can also be used to make SiNa. In the book Lun Heng, Wang Chong of the Eastern Han Dynasty made a clear record of the shape and usage of Sina. Sina is made of a whole natural magnet after pondering. The handle of the spoon is guided by the pole, so that the center of gravity of the whole spoon falls right in the middle of the bottom of the spoon. The spoon is placed in a smooth field, surrounded by a four-dimensional stem and branches, which synthesize 24 directions. This design was completed through long-term research after the ancients carefully observed many phenomena related to magnetism in nature and accumulated a lot of knowledge and experience. The appearance of Sina is the practical application of people's understanding of the polarity of magnet fingers. However, Sina also has many defects. Natural magnets are hard to find, and they are easy to lose their magnetism when they are impacted and heated during processing. Therefore, Sina's magnetism is relatively weak, and the contact with the site should be very smooth, otherwise it will be difficult to rotate because of too much friction and resistance, and the expected guiding effect will not be achieved. Moreover, Sina has a certain volume and weight, which is inconvenient to carry, which may be the main reason why Sina has not been widely used for a long time. Sina consists of a bronze disc and a magnetic spoon made of a natural magnet. The bronze disc is engraved with 24 directions, and the magnetic spoon is placed on the central circular surface of the disc. When it is at rest, the tail of the spoon points to the south. The invention of the compass In ancient times, people often cut thin iron leaves into the shape of fish. The belly of a fish is slightly concave, like a boat. Float on the water surface after magnetization, which can refer to north and south. It was used as a game at that time. Cui Bao of the Eastern Jin Dynasty once mentioned this kind of "guiding blind fish" in Notes on Ancient and Modern Times. Ceng Gongliang in the Northern Song Dynasty recorded the method of making and using the fish guide in the General Introduction to the Five Classics: "Cut it with thin iron leaves, two inches long and five points wide, with the head and tail as sharp as a fish's tip, and burn it with charcoal. Hou Tongchi, with iron wok and iron pot fish as the initial fire, the tail is straight, dipped in the basin and sealed. When in use, put the water bowl flat in a windless place, and the fish will float on the water. Its first direction is always noon. " This is an artificial magnetization method, which uses the earth's magnetic field to magnetize the iron sheet. That is, put the red-hot iron sheet in the meridian direction. The molecules inside the hot iron sheet are in a relatively active state, which makes the iron molecules arrange along the direction of the earth's magnetic field to achieve the purpose of magnetization. This arrangement can be quickly fixed by immersing it in water, and the degree of magnetization can be increased by tilting the fish tail slightly downward. The invention of artificial magnetization has played a great role in the application and development of compass. This is also a great event in the history of the development of magnetism and geomagnetism. Shen Kuo in the Northern Song Dynasty mentioned another method of artificial magnetization in Meng Qian Bi Tan: "Fang Jia can be guided by a magnet." According to Shen Kuo, technicians at that time rubbed sewing needles with magnets to make them magnetic. From now on, this is a method to make the arrangement of magnetic domains in the steel needle tend to a certain direction by using the magnetic field of natural magnets, thus making the steel needle appear magnetic. This method is simpler than geomagnetic method, and the magnetization effect is better than geomagnetic method. The invention of friction method is not only the earliest in the world, but also creates conditions for the emergence of practical magnetic direction finder. Shen Kuo also talked about various phenomena in the process of friction magnetization in Meng Qian's Notes: "If a magnet is used for tit-for-tat, it will be sharp and always guided. Some people point to the north and are not afraid of stones ... On the contrary, there should be differences between the north and the south, which has not been studied in depth." That is to say, after rubbing the sewing needle with a magnet, it sometimes points to the north in a tit-for-tat manner. From now on, all magnets have two poles, N and S, and the direction of the sewing needle is different when magnetized, so the direction after magnetization is also different. But Shen Kuo didn't know this truth. He truly recorded this phenomenon and frankly admitted that he didn't think deeply. I hope future generations can explore further. Regarding the installation method of magnetic needle, Shen Kuo introduced four methods: 1. Shui Piao method-Put some rushes on the magnetic needle to float on the water, which can indicate the direction. 2. Bowl lip rotation method-put the magnetic needle on the edge of the bowl mouth, and the magnetic needle can rotate to indicate the direction. 3. nail rotation method-put the magnetic needle on the nail. Because the nail surface is smooth, the magnetic needle can rotate freely to indicate the direction. 4. Twilight hanging method-coat some wax in the middle of the magnetic needle, stick a silk on it, and hang it in a windless place to indicate the direction. Shen Kuo also compared four methods. He pointed out that the biggest disadvantage of water flotation is that the water surface is easy to shake, which affects the measurement results. Bowl lip rotation and nail rotation are flexible because of low friction, but they are easy to fall off. Shen Kuo emphasized the hanging method, which he thought was an ideal and practical method. In fact, the four methods pointed out by Shen Kuo have summarized the two systems of compass devices so far-water needle and dry needle.