Weather magnet

The ancients found that natural magnets have the characteristics of indicating north and south long ago, and the earliest tool to indicate north and south-Sina-was made of natural magnets. However, natural magnets are very fragile and easily damaged during cutting. After being hit or heated, their magnetism will weaken or even disappear. So, after repeated experiments, people invented all kinds of artificial magnets.

According to Ceng Gongliang's "Wu Jing Zong Yao" in the Northern Song Dynasty, when the direction cannot be identified due to weather, the blind fish can be used to identify the direction. The guide fish mentioned here is a guiding tool. As the name implies, the shape of a guide fish is a fish. This fish is made of thin steel plate, two inches long and five points wide. When you need to point, just put it in a bowl of water and the head of the floating fish will always point south.

Steel sheet itself is not magnetic, how to guide it? There is only one answer-the steel sheet must be magnetized to become a magnet. The method of magnetization is given in the general theory of Wu Jing: cut the iron sheet into the shape of a fish, burn it red in charcoal fire, take it out, clamp it with pliers, and put it in water to cool it. When cooling, the fish should be placed along the meridians at a certain angle to the horizontal plane. In this way, a guide fish that can indicate the direction is made.

The ancients gave the method of magnetization, but did not explain the principle. Modern physicists have given a scientific explanation: this magnetization method is called geomagnetic method, which uses the magnetic field of the earth itself to magnetize. When heated at high temperature, the molecules in the iron sheet move faster. Due to the influence of the earth's magnetic field, the magnetic domains in the iron sheet are arranged in order according to the direction of the magnetic field. At this time, once the iron sheet is put into cold water, it suddenly cools, and the magnetic domain is fixed, becoming a permanent magnet.

Shen Kuo, a scientist in the Northern Song Dynasty, mentioned another method of artificial magnetization in Meng Qian's Bi Tan, saying: "If you use magnets to confront each other, you can guide them." . Technicians use magnets to polish the needle tip, so that the magnetization of the needle tip plays a guiding role. This is to use the magnetic field of natural magnet to make the arrangement of magnetic domains in the steel needle tend to the same direction, so the steel needle obtains magnetism.

Summary: The ancients made magnets by artificial magnetization, which made the magnetic conductivity more and more stable and reliable, and played a great role in the application and development of compass.