In addition to the ground motion instrument, Zhang Heng also had these inventions

Source: Science and Technology Daily

Zhang Heng was a famous writer and scientist in the Eastern Han Dynasty of China, and his deeds of inventing the ground motion instrument are not only recorded in the history books, but also included in the textbooks, and almost everyone in China is familiar with it. In addition to inventing the ground motion instrument, Zhang Heng has many ingenious ideas and productions, and has made important contributions to the development of astronomy, meteorology, mathematics, and mechanical production in China.

Zhang Heng (張衡), also spelled Pingzi, was a native of Nanyang Xi'e during the Eastern Han Dynasty, which is today's Nanyang, Henan. He was born in a family of eunuchs, and his grandfather Zhang Kan had served as the Taishou of Shu County and the Taishou of Yuyang, and was very famous in the local area, but with the death of his grandfather, the family was in decline, so he lived a poor life from an early age. Although he lived in poverty, Zhang Heng was talented, diligent and studious, and was very good at writing articles at a very young age. As the saying goes, "It is better to read ten thousand books than to travel thousands of miles", at the age of 17, Zhang Heng decided to travel abroad, he first came to the Sanfu region, that is, the Western Han Dynasty with the capital Chang'an as the center of Jingzhao, Zuo Fengyi, and Right Fufeng, equivalent to today's central Shaanxi region, and then from Sanfu to Luoyang, the capital of the capital, where he read the Five Classics, penetrated the Six Arts, and became close friends with young scholars such as Ma Rong and Cui Zhen.

Although his learning was outstanding, Zhang Heng was not keen on fame, and it was not until the age of 23 that he agreed to the invitation of Taishou Baode of Nanyang County and served as the lord of Nanyang County. After returning to Nanyang, he carefully studied astronomy, yin and yang, and calendar arithmetic, which attracted the attention of Emperor An of Han, and specially recruited him as Langzhong, and soon promoted him to Taishi Ling, who was in charge of the celestial time and the ephemeris. During his tenure as Taishi Ling, Zhang Heng wrote works such as "Lingxian" and "TheOry of Calculation and Recklessness", and also produced armillary celestial spheres.

In the book, Zhang Heng comprehensively expounded the generation and structure of the heavens, the origin and evolution of the universe, the nature of the sun, moon and stars, and for the first time correctly explained the causes of lunar eclipses, greatly improving the level of ancient astronomy in China and making it a leading position in the world. "Arithmetic Theory" is An important work of Zhang Heng in mathematics, although it has been lost, but Liu Hui quoted some of Zhang Heng's views in the "Nine Chapters of Arithmetic Notes", from which we can know that Zhang Heng proposed π = √10, which played a role in promoting Zu Chongzhi's calculation of pi.

The armillary sphere is an ancient instrument for observing celestial phenomena. During the Eastern Han Dynasty, there were two main theories about the universe, the Gaitian theory and the Huntian theory, the Gaitian theory believed that the earth was flat, and the heavens were like a bowl clasped on the ground; the Huntian theory believed that the heavens were like eggshells, and the earth was like egg yolks. In contrast, hun tian theory has more supporters, they have made a lot of instruments for observing celestial phenomena, known as armillary celestial instruments, such as the Han WuDi period of the fall of the Hong Kong once made armillary celestial spheres. On the basis of inheriting and developing the achievements of his predecessors, Zhang Heng transformed the armillary celestial sphere. He first made a small model of bamboo, called Xiaohun, and spent a whole year, after many experiments and improvements, before casting it in copper.

The Book of Jin and Astronomical Records has a detailed record of the armillary sphere that Zhang Heng transformed, and from the records, it can be known that the main body of the armillary sphere created by Zhang Heng is a large copper ball, similar to the current celestial sphere. There are stars such as the North and South Poles, the Ecliptic, the Equator, the Twenty-Four Solar Terms, the Twenty-Eight Stars, and the Sun and Moon. In the place where the copper ball is equivalent to the north and south poles, there is a shaft that can be rotated. There are also two rings outside the sphere, of which the ring that passes through the north and south poles is called the meridian circle, and the other is the horizon circle that represents the horizon. After the copper ball rotates from west to east, you can see the stars carved on it rise above the horizon and fall below the horizon as they rotate, just as the stars in the sky rise in the east and set in the west. The great thing about Zhang Heng's armillary sphere is that he turns the copper ball with water power through design, and makes the copper ball rotate at the same speed as the earth rotates for a week. Therefore, when the copper ball is turned, people look at the armillary sphere indoors and can know which star has just risen in the outdoor night sky, which star has reached mid-air, and which star is about to fall.

Even more ingeniously, Zhang Heng also designed a mechanical device called "Ruilun Pod". The so-called wheel refers to the moon, and the pod is a legendary sacred grass. According to the records of the Bamboo Book Chronicle, this sacred grass grew in the ancient era of Saint Wang Yao, and on the day of the lunar calendar, that is, at the beginning of the lunar calendar of each month, a leaf grew every day, and after sixteen days, another day fell a pod, and on the day of the obscure moon, that is, the last day of the lunar calendar of each month, the leaves fell out. If the month is a small month with one less day, the last leaf will wither but not fall. Because this grass can indicate the date and phase of the moon, it is also called "calendar pod". Zhang Heng created a mechanical device based on this legend, which can "rise and fall according to the moon", and it is not an exaggeration to say that it is the calendar of events at that time.

In the early years of the Han Shun Emperor, after two transfers, Zhang Heng became the Taishi Ling again and invented the ground motion instrument. Sometimes, people also call the ground motion instrument The Hou Feng Ground Motion Instrument, but in fact, the Hou Feng Instrument is an invention of Zhang Heng in meteorology, which can be used to measure the direction of the wind, similar to the Hou Feng chicken on the roof of the West, but more than a thousand years earlier than the West.

In terms of mechanical production, according to the Taiping Imperial Records, Zhang Heng once made wooden birds. This wooden bird not only has wings, but also has mechanisms in the bird's belly, and with the help of mechanisms and wings, the wooden bird can fly for miles. In addition, Zhang Heng has also made a machine with three wheels that can rotate, some people think it is a kind of drum car, but some people think that this is a guide car. These ingenious machines have been lost, but the relevant records left in the books are enough to prove Zhang Heng's superb skills in mechanical production. Ge Hong of the Jin Dynasty referred to Zhang Heng and Ma Jun, a mechanical master of the Three Kingdoms period, as "Mu Sheng".

Zhang Heng's creations and inventions are impressive, and his contemporaries, scholar and friend Cui Yan, once said that he was "a great artist with great skills and a brilliant performance." Guo Moruo, a former president of the Chinese Academy of Sciences, once said that he was a rare well-rounded figure in world history. Today, Zhang Heng's name is not only recorded in various scientific and technological history texts, but also forever engraved on celestial bodies. In 1970, the International Astronomical Union named a crater on the moon "Zhang Heng Mountain", and seven years later, the asteroid in the solar system numbered 1802 was named "Zhang Heng Star".

The author is a lecturer at Jinan Institute of Chinese Culture (Jinan Socialist College).