Fish made of steel sheet is not magnetic, so it has no guiding function. If you want it to be a guide, you must also use artificial magnetic transfer to make it a magnetic magnet.
As for how to transmit magnetism artificially, General Theory of Martial Arts records that red-hot iron pieces are placed in the direction of meridians. After the iron sheet burns red, the temperature is higher than the magnetic transition point, and the disordered magnetic domains in the iron sheet collapse and become paramagnetic. After quenching in water, the magnetic domain is formed again, but under the action of geomagnetic field, the magnetic domain is oriented, so it can refer to north and south.
The ancients in our country invented artificial magnets as guide fish, which is a great progress. This shows that the ancients in China had quite rich knowledge of magnets a long time ago.
Shortly after the invention of the steel needle, someone invented the steel needle to guide. This artificially magnetized small steel needle can be regarded as the first real compass made in the world.
Shen Kuo, a scientist in the Northern Song Dynasty, mentioned an artificial magnetization method in Meng Qian Bi Tan: technicians rubbed sewing needles with magnets, and the needles were magnetized.
From now on, this is a magnetic field effect of natural magnets, which makes the arrangement of magnetic domains in the steel needle tend to a certain direction, thus making the steel needle 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. Regarding the installation method of the magnetic needle, Shen Kuo mainly introduced four methods: one is the Shui Piao method, that is, putting a few wicks on the magnetic needle to make it float on the water, which can indicate.
Direction. The second is the bowl lip rotation method, that is, the magnetic needle is placed on the edge of the bowl mouth, and the magnetic needle can rotate to indicate the direction. The third method is nail rotation, and the magnetic needle is placed on the nail. Because the nail surface is smooth, the magnetic needle can rotate freely to indicate the direction. The fourth is the hanging method, which is to coat some wax on the middle part of the magnetic needle, stick a silk on it and hang it in a windless place, so as 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 praised the hanging method as an ideal and practical method. Shen Kuo pointed out four methods, which summarized two systems of compass device so far, namely water needle and dry needle.
In addition, because the geomagnetism in the Yangtze River and Yellow River basins has an inclination of about 50 degrees, if the compass fish is placed horizontally, only the horizontal component will play a role. If it is placed in water at a certain angle, the effective magnetic field intensity of the fish magnetization will increase and the magnetization effect will be better.