China is one of the first countries to record magnetic phenomena in words. There is a description of "copper and gold under the stone" in Guanzi in the Warring States Period in the 4th century BC. This is the earliest record of magnets and magnetic minerals. In the Spring and Autumn Annals written by Lu in the 3rd century BC, the phenomenon that magnets attract iron was described. The application of magnetic phenomenon is mentioned in the book "Notes on Water Classics" at the end of Wei Dynasty in ancient China. In order to prevent assassins with swords from entering, Qin Shihuang built the north gate of Epang Palace with magnets. Medical books have also talked about using magnets to absorb iron to treat needle swallowing, but the most brilliant achievement in the early application of magnetic phenomenon is the invention and application of compass, which is also a great contribution of China to mankind. The orientation of magnets was discovered in China during the Warring States Period. The magnet in the earliest guide is a spoon-shaped magnet called Sina. Although its sensitivity is very low, it gives people enlightenment: there is a kind of geomagnetism, and magnets can point. In the Northern Song Dynasty, a new pointing tool-compass fish came out. In Ceng Gongliang's Wu Jingzong Yao, the manufacturing process of compass is recorded in detail. There is a major breakthrough here, that is, the fish-shaped iron is magnetized into a pointer by magnetization. Since then, the manufacturing and installation methods of compass have been clearly recorded in Meng Qian Bi Tan written by Shen Kuo in the Northern Song Dynasty. Soon the compass and the azimuth disk were combined into a compass, which provided a convenient and reliable pointing instrument for navigation. Later, our compass spread to Europe. By16th century, the navigation compass appeared in Europe. The invention of compass promoted the development of navigation and created conditions for studying the three elements of geomagnetism. Gilbert, an Englishman, has made outstanding contributions to the study of magnetism. His book Magnetism marks the beginning of a systematic study of magnetic phenomena, which was published in 1600. The book records all kinds of instruments and experimental processes Gilbert made when he studied magnetic phenomena, and also records the conclusions he got from the experiments. According to the arrangement and orientation of magnetic needles, he proposed that the earth itself is a big magnet, and its poles are located near the north and south poles of geography. Put forward the concept of magnetic meridian; Gilbert also explained the measurement methods of magnetic declination and geomagnetic inclination; The concepts of magnetization and demagnetization of iron; Qualitative research on attraction and repulsion of magnets. All these pave the way for the further study of magnetism. By the18th century, new progress had been made in the study of magnetism. Coulomb, a French physicist, also made outstanding contributions to the study of magnetism. He took part in a competition organized by French Academy of Sciences to design a compass with strong pointing and good anti-interference performance, and put forward the idea of hanging the compass with silk, and won the magnetic prize. On this basis, he made a Coulomb torsion balance. Coulomb's law of charge interaction is established and the law of magnetic interaction is obtained. It can be said that Coulomb was the first founder of electrostatics and magnetostatics. After that, Poisson, a French mathematician and physicist, put forward the potential function integral equation of the interaction between magnets on the basis of Coulomb, which developed the study of magnetism to the quantitative stage, but at this time electricity and magnetism were still studied independently in parallel. The Danish physicist Oster discovered the magnetic effect of current in 1820, which caused great repercussions and concerns in the scientific community at that time. Scientists have turned to the discussion and research in this field, which has promoted the development of the whole electromagnetism. Ampere thinks from the magnetic effect of current: since there is interaction between magnets and there is interaction between current and magnets, there must be interaction between two current-carrying conductors. Through a series of experiments, he found the experimental basis of the interaction between currents, made quantitative research, and submitted papers to the Academy of Sciences on February 4, 1820, 1820, and put forward a formula for calculating the force between two current line elements-Ampere's law expression. 182 1 At the beginning of the year, Ampere further put forward the magnetic origin hypothesis, which is the famous molecular current hypothesis in history. Ampere discovered the interaction between current-carrying conductors on the 7th day after Oster discovered the current magnetic effect. A wave of new discoveries is pounding the whole of Europe. Facing the new discovery, Faraday redone the existing experiments and put forward a new research topic-since electricity can produce magnetism, why can't magnetism produce electricity? He started the research of magnetic power generation. After 10 years of efforts, on the basis of a large number of experiments, the electromagnetic induction phenomenon and its law have been discovered. The discovery of electromagnetic induction has epoch-making significance. Faraday finally linked the two phenomena of long-term separation of electricity and magnetism, revealed the essential relationship between electricity and magnetism, and found the conversion method between mechanical energy and electrical energy. Theoretically, it lays a foundation for establishing the theoretical system of electromagnetic field; In practice, it initiated a new era of electrification. After Faraday discovered the phenomenon of electromagnetic induction, he explained the experiment named "Mystery" made by French scientist arago-placing a freely rotating circular copper disk under a suspended magnet, and when the disk rotates, the magnet will also rotate; Conversely, when the magnet rotates, the copper disk will also rotate. Faraday put forward the concept of magnetic induction line (magnetic field line) and drew the magnetic induction line diagram for the first time. He believes that magnetic induction line is a material entity representing reality; Each magnetic induction line corresponds to a pair of magnetic poles. Later, the space with magnetic induction lines was called "field". Maxwell is a famous British physicist. He developed Faraday's idea of "force field line" and mathematicized it, put forward an equation describing the law of electromagnetic field movement, and predicted the existence of electromagnetic waves. German physicist Hertz convincingly proved the existence of electromagnetic waves through experiments. This not only verifies the correctness of Maxwell's electromagnetic field theory, but also lays the foundation for the establishment and development of radio technology. Einstein's special theory of relativity established in 1905 unified two natural forces-electricity and magnetism for the first time. With the invention of modern electronic computers, new magnetic materials are constantly emerging. Human science and technology and material production activities are inseparable from electricity and magnetism, but the exploration of magnetism is endless. With the discovery of new magnetic phenomena and the exposure of the deeper essence of magnetism, the application of magnetism will also present a new situation. Write a new chapter for the development history of magnetism.