Development history of geomagnetism
China first discovered the phenomenon of magnet and geomagnetism, invented the compass in BC, and used the compass to navigate from 838 to 1099. Compass has been used in Europe since the 12th century. The Italian navigator C. Colombo (1451 ~ 1506) discovered the magnetic declination when he sailed from Europe to America. In 1510, G. Hartman first discovered the magnetic inclination in Rome. In 1600, the British scholar W. Gilbert pointed out that the earth is a huge spherical magnet. This is the earliest discussion on the origin of geomagnetic field. By the end of the 17th century, all geomagnetic observations were limited to measuring magnetic declination and inclination, and the magnitude of magnetic force could not be measured. In 1839, the classic work "absolute strength of geomagnetism" by the German physicist c.f. Gauss (1777 ~ 1855) came out, created the spherical harmonic analysis method of geomagnetic field, confirmed Gilbert's view, and laid the theoretical foundation for quantitative analysis of geomagnetic field. According to Gauss theory, the magnitude of geomagnetic force can be measured. In 1840, Gauss published an introduction to geomagnetism, which made a thorough digital analysis of the geomagnetic field and laid the foundation for the theoretical analysis of the geomagnetic field.
At the same time, Russian scholar Simonov（ И.Симонов， 1794 ~ 1855) published the tentative theory of geomagnetism in 1835, pointing out that the geomagnetic field is the product of the action of evenly distributed magnetic particles in the earth's interior. Gauss and Simonov were pioneers in the study of geomagnetism. Geomagnetic survey began in the 16th century. In 1538, J.D. Castro accurately measured the offshore magnetic declination from Europe to East India. In 1832, Gauss founded the method of measuring the absolute value of geomagnetic field intensity, and jointly founded the "Gauss unit system" with the German physicist W.E. Weber (1804 ~ 1891), which accelerated the measurement of geomagnetic field in various countries. In the 19th century, the application of geomagnetic anomaly to find magnetite promoted the application research of Geomagnetism and the research of magnetic survey methods. In the 1920s, the first geomagnetic stations were established all over the world. From 1957 to 1958, the International Association for science and technology organized three geomagnetic seminars, comprehensively discussed the temporal and spatial distribution characteristics of the geomagnetic field and various geomagnetic phenomena, and enriched the geomagnetic theory. Nowadays, the study of rock paleomagnetic field promotes the study of plate tectonics. Geomagnetism is developing towards the application stage.
The research content of geomagnetism is divided into two systems: ① the basic magnetic field of the earth. It includes the basic law of stable magnetic field, geomagnetic field elements and research methods, geomagnetic field structure and long-term changes. The theoretical basis of ferromagnetic phenomena, the study of rock magnetism, the basic principles and research methods of paleomagnetism; ② The changing magnetic field of the earth. Including the change of geomagnetic field and its research direction, periodic geomagnetic change, geomagnetic disturbance, various natural phenomena accompanying geomagnetic change, Aurora and magnetic disturbance theory. Nowadays, the research of geomagnetism tends to develop from the ground and ocean surface to the high altitude. Magnetic detectors are placed on rockets and man-made satellites to receive data related to the high altitude atmosphere, solar wind, planetary interstellar magnetic field and geomagnetic field. Computer will play an important role in dealing with the calculation of various complex geomagnetic anomalies and the data processing of original data.