High quality NdFeB Magnet from east

In writings from the Spring and Autumn Period and the Warring States Period, the iron-attracting properties of magnets were repeatedly recorded. For example, the "magnetic stone summons iron" in the "Lu Shi Chun Qiu" written in the third century BC, and the "magnetic stone summons the needle" in the "Guiguzi" not far away from each other are both. At this time, magnetism was probably more commonly recognized and compared to the attraction of a loving mother to her children.

Gao Yao of the Eastern Han Dynasty said in his annotation of "Lu Shi Chun Qiu": Stone is the mother of iron, but there are kind and unkind stones. A kind stone can attract its children (iron), but an unkind stone cannot attract it. . Therefore, before the Han Dynasty, magnets were written as "Ci Shi", which means "Stone of Kindness".

Later, people inevitably used magnets to try to attract other metals or objects. What was the result?

The book "Huainanzi" written in the Western Han Dynasty wrote: "If a kind stone can connect iron, it will be difficult to use it to lead tiles." "It cannot connect to copper." During the Three Kingdoms period, someone also said: "The stone of kindness cannot be bent." The so-called "curved needles" probably refer to needles made of metals such as gold, silver, and copper, which are of course not attracted by magnets.

These records show that the Han Dynasty realized that magnets can only attract iron but not other things. This is a bit of progress. We know that magnets can only attract each other to iron, but if magnets are close to each other, the situation is a bit more complicated. Magnets always have two poles, one is called the south pole and the other is called the north pole.  At that time, there was an alchemist named Luan Da who made two magnets, which looked like chess pieces and were close to each other. It was said that they could not only attract each other ("cancel each other"), but also "repel each other endlessly", that is, repel each other. This is the so-called "fighting chess" trick. He performed this trick to Emperor Wu of the Han Dynasty, and the emperor was amused, so he obtained the official position of "Five-profit General".