Chapter 19 Chapter 19 The invention of the compass in my country and its application to navigation

As early as the Warring States period, our ancestors understood and used the polarity of the magnet to make the earliest compass - Sinan.Much more convenient than a compass car using gears.In the ancient books of our country, "magnet" is written as "kindness stone", which shows that our ancestors discovered the property of magnetite to absorb iron 2,000 years ago, and believed that the relationship between magnetism and iron is as close as a loving mother and her children. Magnets are magnetic, and the magnetism of each magnet is always gathered at the two ends, and the central part is almost non-magnetic, and the two poles with magnetism are called magnetic poles.If a rod-shaped magnet is tied in the middle with a rope to make it hang in the air, after it is moved, when it stops, one end must point to the south and the other end to the north.What is the reason?It turns out that the whole earth is a big magnet, and it also has two magnetic poles, the magnetic north pole is near the earth's south pole, and the magnetic south pole is near the earth's north pole.Each lodestone also has two magnetic poles, north and south.Different poles attract each other, and like poles repel each other.Due to the principle of "opposites attract, same sex repel", the suspended magnet is facing south at one end and north at the other.If you put another magnetic rod next to the suspended magnetic rod for experiment, you can see that one end attracts each other and the other end repels each other.Therefore, the magnetic south pole of the suspended magnet will attract the magnetic north pole of the earth and point to the south, and its magnetic north pole will attract the magnetic south pole of the earth and point to the north.This property of magnets is called polarity.Based on this characteristic of magnets, our ancestors created various tools for indicating directions.

"Han Feizi" in the Warring States Period mentioned Sinan made of magnets.Sinan is the meaning of guide, and Wang Chong, a thinker in the Eastern Han Dynasty, also recorded Sinan in his book "Lunheng".Sinan consists of two parts: a "spoon" and a "site".Sinan spoons are made from a single piece of magnet.Its magnetic south pole end is cut into a long handle, and the round bottom is its center of gravity, which is very smooth.The site is a copper square plate with a smooth circular groove in the center surrounded by grid lines and characters representing 24 directions.Since the bottom of Sinan and the circular groove of the chassis are very smooth, Sinan can rotate flexibly when placed in the chassis. When it is at rest, the polarity of the magnet makes the long handle always point to the south.This instrument is the predecessor of the compass. Since the use of Sinan must be equipped with a site, the compass is also called the compass needle.

During production, natural magnets tend to lose their magnetism due to impact and heat, and their magnetism is weak, so Sinan cannot be widely circulated.In the Song Dynasty, someone discovered artificial magnets.When steel is ground on a magnet, it becomes magnetic. This kind of magnetism is relatively stable and not easy to lose.Later, guide fish appeared in long-term practice.About 1044 A.D., Guanxiu and Zeng Gongliang's "Wu Jing Zong Yao" recorded guide fish made of artificial magnets.The production method is: "cut it with a thin iron leaf, two inches long and five minutes wide, with the head and tail sharp like a fish, burn it in a charcoal fire, wait for it to turn red, use an iron seal to seal the head of the fish, and put the tail in front of the child, dip it in In the water basin, stop if there is no mantissa, and store it in a secret device." This is a method of magnetizing iron pieces by using the strong earth's magnetic field.When in use, place the water bowl flat in a windless place, the fish floats on the water surface, the fish head is the magnetic north pole, the fish tail is the magnetic south pole, the fish can rotate freely in the water, and the fish head always guides.When marching, soldiers carry guide fish, which can avoid getting lost in cloudy days, but the magnetism is still low, and the practical value is not too great.

Improve from the guide fish, change the magnetic sheet into a magnetic steel needle, and create a new guide instrument that is further than the guide fish.A small steel needle used for sewing is ground on a natural lodestone to make it magnetic, and the compass with an artificial magnet is thus produced. Shen Kuo, a man of the Song Dynasty, recorded four experiments on the use of a compass in his book "Mengxi Bi Tan".The first one is called "water float method", in which a few short pieces of lamp grass are crossed on the magnetic steel needle, so that the magnetic needle can float on the water surface, which has the same effect as the compass fish.However, if it is shaken, the magnetic needle will wobble on the water surface, and the guide may not be accurate.The second method is called "nail rotation method", and the third method is called "bowl lip rotation method", which is to put the magnetic needle on the fingernail or on the edge of the bowl. Both the fingernail and the edge of the bowl are relatively smooth, so that the magnetic needle can It turns freely and flexibly, but the magnetic needle is easy to slip off, which is not very convenient to apply.The fourth method is called "spinning method" (i.e. "hanging method"), which is to attach one end of the single thread to the waist of the needle with wax and hang it in a windless place. The single thread is a single thread taken out of a new cocoon, and its elasticity and toughness are both Better, there will be no torsion problems.Use mustard-sized wax to glue the single wire and the magnetic needle together, and do not use the kink method, which is to prevent the occurrence of torsion problems.Shen Kuo believes that the "twirl method" is the most perfect.

"Mengxi Bi Tan" also records an important discovery on the nature of magnets: the guide of magnets does not point to the right direction.Shen Kuo estimated that it is a bit easterly, because the two poles of the earth's magnetic field do not coincide with the two poles of the earth's meridian, and the magnetic line of force forms a certain angle with the meridian, which is called "geomagnetic declination".Later generations accurately pointed out that the declination angle is within about 5°.Moreover, it is different across the country. Shen Kuo's discovery of "geomagnetic declination" is a major contribution of the Chinese to the world.In Europe, the "magnetic declination" was not discovered until Columbus sailed across the Atlantic Ocean in 1492, more than 400 years later than our country.

Soon after the compass was invented, it was used in navigation.The earliest document in the world that records the application of the compass to navigation is "Pingzhou Ketan" written by Zhu He [yuyu] during the Xuanhe period of the Northern Song Dynasty (1119-1125 A.D.) (the book was written slightly later than "Mengxi Bitan"). His father, Zhu Fu, served as a senior official in Guangzhou from 1094 to 1102. He followed his father and lived in Guangzhou for a long time.The book records what he saw and heard when he was in Guangzhou.At that time, Guangzhou was a large port for trade between my country and overseas. There was a shipping department for the management of seagoing ships, and a Fanfang for overseas businessmen to live in. The maritime industry was quite developed. "Pingzhou Ketan" records many situations such as Guangzhou Fanfang and Shiship, and records the experienced sailors on Chinese sea ships.They are good at distinguishing the direction of the sea: "The boat master knows the geography, the stars at night, the sun in the daytime, and the compass in the dark." .It shows that the people of our country already know how to use the compass in navigation.This is the earliest record of the use of the compass in the history of navigation in the world. This instrument navigation method pioneered by the Chinese people is a major innovation in navigation technology.The application of the compass to navigation does not exclude astronomical navigation, and the two can be used together, which can further promote the progress of nautical astronomy knowledge.Xu Jing said in "Xuanhe Envoy Koryo Tujing" (more than 20 years later than "Pingzhou Ketan"): "It's night, you can't live in the ocean, you only look at the stars to move forward, if it's dark, use the compass needle, Take Kui [kui sunflower, measure] north and south." It shows that Xu Jing also used a compass when he was an envoy to Koryo, which is the same as what Zhu or recorded.This is a compass using the water float method, and one is placed at the bow and stern of the ship. When it is cloudy and rainy, the direction is identified by this kind of compass.

Not long after China used the compass to navigate, it was adopted by Arab sea ships, and this great invention was passed to Europe by the Arabs.Engels pointed out in "Natural Dialectics" that "the magnetic needle was passed from the Arabs to the Europeans around 1180". 1180 is the seventh year of Emperor Xiaozong Chunxi in the Southern Song Dynasty of my country.The Chinese first applied the compass to navigation at least 80 years earlier than the Europeans. Chinese ships began to use compass for directional navigation around the first year of Lizong Baoqing in the Southern Song Dynasty (AD 1225). In this year, Zhao Rushi wrote "Zhu Fan Zhi", which is a work that records the geographical conditions of overseas countries.It is mentioned in the book that he took a sea boat from Quanzhou to Hainan Island: "Boats and ships travel, but the compass is the only rule. Watching day and night is only cautious, and the difference between life and death is a matter of life." It can be seen that the compass pointed during the voyage The role of direction has become more important.Compared with the situation in the 11th century when the compass was only used on rainy days, it was only used as an auxiliary instrument to indicate the direction. What is mentioned in "Zhu Fan Zhi" is not a compass but a compass.If there is no pointing scale on the compass, it is impossible to "keep the eye but be careful" and "the slightest difference".Wu Zimu of the Southern Song Dynasty wrote "Meng Liang Lu": "When the wind and rain are dark and dark, you can only walk with the needle, and the fire chief (captain) is in the palm of it. You dare not make a slight mistake, and the life of a boat is tied." It can also be seen that the compass aims at The importance of sailing.

The application of compass needles in navigation shows that my country's navigation technology was in the leading position in the world in the Song Dynasty.In the Southern Song Dynasty, Guangzhou, Quanzhou, and Hangzhou were all large commercial ports. At that time, more than 50 countries were in business with my country, and Arabs, Persians, and Romans came to my country for business by sea.At that time, the tax revenue from commerce accounted for 1/20 of the total tax revenue of the national treasury. Without the invention of the compass, it would be impossible to have such a prosperous maritime commerce and trade.The invention of the compass and its spread to the west promoted the economic and cultural exchanges between my country and the countries along the Indian Ocean and the western Pacific Ocean at that time, promoted the development of navigation in various countries, and created the prerequisites for Columbus's "discovery of the New World" in 1492.The invention of the compass and its application to navigation have made significant contributions to the world.