Exploration before the Space Age: Reminiscing about childhood in space physics (2)

Author | Dayan

In addition to the gorgeous and charming aurora, geomagnetic phenomenon is another phenomenon supporting space physics. It mainly means that the magnetic field on the ground changes with time, and most of these changes are affected and controlled by solar activity.

People's understanding and utilization of geomagnetic phenomena can be traced back to the Warring States Period and even the Yellow Emperor Period. It is said that Huangdi Xuanyuan encountered heavy fog when he was fighting Chi You, so he made a compass to identify the direction. This kind of guide car is likely to use the principle of a magnet guide. In Ci County, Hebei Province, there is a Ci Mountain. According to the "Ancient Mine Records" compiled by Zhang Hongzhao, a stone with "suction power" was produced here as early as the Warring States Period. Because the kind mother also had "suction power", it was first called "Ci Shi". Later, with the evolution of Chinese characters It is called "magnet". "Guiguzi" records: "When Zheng people collect jade, they must carry Sinan's cart, so they are not confused." It shows that when people mined jade at that time, they had already used a compass to indicate the direction. "Huainanzi Shuo Shan Xun" records: "Magnet can attract iron, but not copper." This clearly describes the understanding of magnets at that time. During the reign of Emperor Wu of the Han Dynasty, Luan Da, a "Jiaodong palace man" who boasted in front of the emperor that he could reach the gods, used chess pieces made of magnets to "test the small squares" for the emperor, and was named "Five-profit General" by the emperor. During the Eastern Han Dynasty, Wang Chong's "Lunheng Shi Ying Pian" said: "Sinan's spoon, thrown to the ground, is a guide." This shows that before the Eastern Han Dynasty, our country had already used magnets to indicate directions - polishing the magnets Shaped into a spoon and placed on a square plate marked with directions, this is Sinan. Later, magnets were made into long strips, needle shapes, fish shapes, etc., and fulcrums, wire suspensions, and water floats could be used to ensure the free rotation of the magnets. In the Tang Dynasty, the magnets were widely used in the "Kanyu technique" of Feng Shui, and they were made into shapes marked with The compass marked by Bagua directions and Feng Shui determined the directions for the mansions, palaces and tombs of the nobles and royal families at that time. Shen Kuo's "Mengxi Bi Tan" of the Song Dynasty recorded the practice of the compass in detail: "The Fang family uses magnets to sharpen the tip of the needle, so that it can guide, but it is often slightly to the east and not completely south. The water floats a lot, and the fingers and claws touch the bowl. It can be done on the lips, and it works very quickly, but it is slippery and easy to fall, so it is best not to hang it like a thread. The method is to take a single cocoon thread in Xindu, embroider it with mustard seed wax on the waist of the needle, and hang it in a windless place. The Needle Guide." This is believed to be the earliest record of a compass. In fact, the compass has gone through a long period of evolution, and its practical application history should be earlier than the records in "Mengxi Bi Tan".

In 1119, "Pingzhou Ke Tan" by Zhu Yu of the Northern Song Dynasty recorded the method of identifying the direction when sailing at that time: "The boat master knows the geography, observes the stars at night, observes the sun during the day, and observes the compass when it is obscure. "Look at the stars at night, the sun during the day, and rely on the compass to determine the direction on cloudy days. The compass was introduced to the West and was also used for navigation. In the second half of the 12th century, there was a monk named Alexander Neekan in the British town of St. Albans. He recorded in his writings that a magnetic needle could point to the north. By using a fulcrum to support the magnetic needle, it could be used to point to the north. The time of day indicates the direction. Official records from the 14th century indicate that compasses were widely used by Europeans to navigate ships at sea.

"Mengxi Bi Tan" also describes that the magnetic needle (South Pole) "usually tilts slightly eastward, not completely southward", which is consistent with the magnetic declination (North Pole) tilting westward in most parts of my country. . Europe's understanding of magnetic declination was more than 300 years late. In 1544, Georg Hartmann, a priest in the small town of St. Zebald in Nuremberg, Germany, wrote in a letter that the magnetic declinations of Rome and Nuremberg measured in 1510 were 6 degrees and 10 degrees eastward respectively.

The geomagnetic field not only has a magnetic declination in the horizontal plane, but also a magnetic inclination in the vertical plane, which is the angle between the direction of the geomagnetic field and the horizontal plane. Europe is leading the way on this point. In 1576, British scientist Robert Norman first measured magnetic inclination. This more or less provided inspiration and clues for William Gilbert. Gilbert was originally a doctor of medicine at the University of Cambridge (later appointed chief personal physician to Queen Elizabeth), but he had long been interested in magnetic phenomena. In his book "On Magnetism" in 1600, he proposed that the earth is a large magnet, called a dipole magnetic field, and gave the direction of the magnetic field at different latitudes.

Gilbert believed that the Earth's magnetic field was constant and relied on it to orient the Earth in space. In fact, the Earth's magnetic field changes with time and has nothing to do with the orientation of the Earth.

British watchmaker George Graham left his hometown at the age of 15 and went to work as an apprentice in a watch shop in London. Later, he not only became a master watchmaker, but also designed and manufactured many watches for famous astronomers such as Halley. Astronomical instruments. In 1722, Graham accidentally discovered that the compass always moved according to a certain pattern. The small magnetic needle pointed differently in the morning and afternoon, and during the day and night. Swedish scientist Anders Celsius also noticed this change. Celsius was the scientist who proposed degrees Celsius. In order to further clarify the laws and causes of changes in the Earth's magnetic field, his assistant Olof Hiorter discovered the diurnal changes in the Earth's magnetic field based on continuous observations over the past three years. This is caused by the ionospheric current vortex in the high-altitude atmosphere that is ionized by the sun above the Earth. As the Earth rotates, observers can sweep through the magnetic field generated by such a current vortex throughout the day, forming the daily pattern of the Earth's magnetic field. change. Sweden is located in Northern Europe, close to the Arctic Circle, so Hiot has natural conditions for observing auroras, and Graham is good at observing subtle changes in the magnetic field. On April 5, 1741, he and Graham of London simultaneously observed changes in the aurora and the geomagnetic field during an aurora outbreak, and found that changes in the geomagnetic field were closely related to aurora activity. This makes the two major phenomena of space physics connected for the first time, and is also the reason why we traced the ancient magnet phenomenon earlier.

At this point, humans have begun to shift from phenomenon cognition and simple application to scientific exploration of magnetic phenomena on the earth. Later, the scientific spirit will be demonstrated in the questioning, thinking and exploration between you and me. Let’s listen to the breakdown next time.

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