While using new guiding tools, the ancients also discovered the phenomenon of geomagnetic declination, which has great inspiration for future generations.
It is said that when Qin Shihuang was in power, he was surrounded by a group of magicians looking for elixirs for him.
One day, a warlock named Xu Fu said, "There are three sacred mountains in the East China Sea, named Penglai, the abbot and Yingzhou, where immortals all live. Ask the emperor to let me lead a group of men, women and children to seek. "
Qin Shihuang was very happy, and immediately sent thousands of children to build a big ship for him, and went out to sea from what is now Rizhao County, Shandong Province, to seek medicine for youth. Who knows that Xu Fu is gone forever? I don't know where he took these boys and girls.
Thousands of years have passed, and Qin Shihuang has already become a historical relic. But the story of Xu Fu crossing the sea to get medicine has not been forgotten. If so, then Xu Fu can be regarded as a pioneer among China navigators.
In fact, the ancient ancestors faced the vast ocean, although they also had the desire to explore the mystery, but they always failed to do so.
It is difficult to go to sea, not because shipbuilding technology restricted the ancient people's overseas communication, but more importantly, because they could not tell the direction at sea at that time. Even if there are ships that can cross the ocean, they will lose their way at sea and eventually die at the bottom of the sea.
Therefore, the invention of the compass can be said to provide eyes for sea-going ships and provide the most basic technical conditions for the development of navigation.
The compass was first invented in China, but it took a long time to gradually develop and improve.
After the invention of Sina, the ancients were able to identify the direction in a long journey. However, Sina has its limitations. When Sina uses magnets, the magnetic poles are not easy to find, and in the process of cutting, the magnets will lose some magnetism because of vibration.
In addition, the Sina chassis must be flat and large when used, which is difficult to be satisfactory when used. Therefore, after the ancients invented Sina, they constantly improved it.
After Sina, our ancestors made a new guide tool, that is, guiding blind fish.
During the Northern Song Dynasty, agriculture, handicrafts and commerce all made new progress. On this basis, China has made brilliant scientific and technological achievements. In the Song Dynasty, China made great progress in the manufacture of compasses, just like papermaking and printing.
At that time, there was an official military work called "General Theory of Wu Jing", which recorded that when marching, if it was cloudy or dark, you should let the old horse lead the way, or use a compass to identify the direction.
The Master Program of Jason Wu was written before 1044. In other words, at that time, there were already guide fish in China and they were applied to the military.
The compass is made of a thin piece of steel and looks like a fish. It is two inches long and five inches wide. The fish's stomach is concave and it can float on the water like a boat.
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 temperature of the magnetic transition point, and the original 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 invention of artificial magnets to make guide fish in China 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 method to make the arrangement of magnetic domains in the steel needle tend to a certain direction by using the magnetic field of natural magnets, thus making the steel needle appear 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 introduced four methods:
One is Shui Piao, that is, put a few wicks on the magnetic needle and let it float on the water, which can indicate the 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.
Geomagnetic dip in the Yangtze River and Yellow River basins, this phenomenon was later called magnetic declination. Shen Kuo wrote in the 24th volume of Meng Qian Bi Tan that the magnetic needle can guide, "However, it is often slightly eastward, not all southward".
This is the earliest existing magnetic declination record in the world. In the west, the magnetic declination was not discovered until 1492 when Columbus crossed the Atlantic Ocean, which was more than 400 years later than Shen Kuo.
Magnetic declination refers to the angle between North Pole and True North when the magnetic needle is at rest. The magnetic declination is different in every place, and because the magnetic poles are also moving, the magnetic declination in a certain place will change accordingly.
Under normal circumstances, the maximum magnetic declination in China can reach 6 degrees, generally two or three degrees. At 25 degrees east longitude, the magnetic declination is between 1 and 2 degrees; In areas above 25 degrees north latitude, the magnetic declination is greater than 2 degrees; If it is in the low latitude area of west longitude, the magnetic declination is 5 degrees to 20 degrees; Above 45 degrees west longitude, magnetic declination is 25 to 50 degrees. Undoubtedly, Shen Kuo's discovery and understanding of magnetic declination inspired future generations.
Chen, a scholar in the Southern Song Dynasty, introduced another method of making fish and turtle guides in The Stone Forest.
This kind of guide fish is different from that recorded in Wu Yao. Carve a fish out of wood, as big as a finger. Put a natural magnet in the belly of the wooden fish, and the S pole of the magnet points to the head of the fish. After sealing with wax, insert a needle from the fish's mouth and it becomes a guide fish. Floating it on the water, a fish head guide, is also a kind of water needle.
Turtle guide was also a popular new device in the Southern Song Dynasty. Place a natural magnet in the abdomen of the wooden turtle, dig a smooth hole under the abdomen of the wooden turtle, align it, and put it on a sharp bamboo nail, which stands upright on the board, so that the wooden turtle is placed on a fixed fulcrum that can rotate freely. Because the friction at the fulcrum is very small, the wooden turtle can rotate the guide rail freely.
This kind of wooden guide fish and turtle was probably created by some alchemists who knew magic, and then it was only used for magic. Therefore, the author of Shi Lin Guang Ji regards them as "immortal illusions".
It was not used for navigation, but for illusion. But this is the pioneer of the drought compass that appeared later.
The invention of artificial magnetization has played a great role in the application and development of compass, and it is also an important event in the history of the development of magnetism and geomagnetism.