Chapter 26 Section 6: Zhang Heng, a scientist who is "unrefined but not drillable"

As mentioned earlier, Zhang Heng is the master of the theory of Huntian, and this is only one aspect of his scientific work.He was an outstanding scientist in the Eastern Han Dynasty and made many scientific and technological contributions. At the same time, he was also a famous writer. Zhang Heng, styled Pingzi, was born in Nanyang (now Nanyang, Henan). He was born in 78 AD and died in 139 AD.Since his youth, Zhang Heng has been very diligent in learning all kinds of knowledge.In order to increase his knowledge, he traveled to the old capital Chang'an (now Xi'an, Shaanxi) and the capital Luoyang when he was young.From then on, he developed the habit of being studious and tireless. "Book · Zhang Heng Biography") as his motto for learning, he not only absorbs the existing knowledge eagerly, but also strives to explore unknown academic fields, so as to make himself a erudite and talented scholar, and is famous for his outstanding scientific and technological contributions history.

Zhang Heng served twice as Taishiling, the official in charge of astronomy, for a total of 14 years, so he made the most outstanding contribution to astronomy.In addition to advocating the armillary theory mentioned above, he improved the armillary sphere, an ancient instrument for observing astrology, and added horizon rings and meridian rings, making the armillary sphere gradually perfect.On the basis of the work of his predecessors, he created an instrument that demonstrates Huntian's thought of water transporting Hunxiang.He represented the celestial sphere with a hollow copper sphere about five feet in diameter, on which he painted the twenty-eight mansions, Chinese and foreign planets, and the ecliptic and equator at a mutual angle of 24 degrees. There are horizon circles and meridian circles outside the sphere. Half hidden under the horizon circle, the celestial axis is supported on the meridian circle, and the celestial sphere can rotate around the celestial axis.He ingeniously connected the clepsydra used to calculate time with the muddy image, taking water leakage as the driving force, utilizing the isochronism of the clepsydra, and through the transmission of the gear train, the muddy image rotates around the axis evenly once a day, so that the muddy image It also automatically and approximately correctly demonstrates the astronomical phenomena.This invention opened the harbinger of the development of water transportation in later generations.

In another book about astronomy, "Ling Xian", Zhang Heng summarized the astronomical knowledge at that time and discussed the thoughts of the creation and evolution of the universe.The book also discusses a series of astronomical phenomena and puts forward many unique insights.He believed that the lunar eclipse was caused by the shadow of the earth covering the moon; he measured the apparent diameter of the sun and the moon to be about 365.25/730 degrees, which is equivalent to 29'.6 in the current 360° system, which is the same as the modern measured sun The apparent diameter of the moon is 32'.0, and the apparent diameter of the moon is 29'.6, which is similar or consistent; There are also fast and slow; he has measured 2,500 stars;...these were quite remarkable achievements at the time.

Zhang Heng also conducted in-depth research on the earthquake problem.He created the world's first seismograph in the first year of Yangjia, Emperor Shun of Han Dynasty (AD 132), called "Houfeng Seismograph".The seismograph is "made of fine copper, with a diameter of eight feet, and the cover is raised, resembling a wine bottle" ("Book of the Later Han Dynasty Zhang Heng Biography"), with an exquisite mechanical structure inside, and a mouth containing small copper balls in each of the eight directions. The dragon, each with a toad with its mouth open under the dragon's head.Once a strong earthquake occurs, the dragon's mouth in the corresponding direction will open, and the copper ball will fall into the toad's mouth, so as to know the time and direction of the earthquake.According to records, on the third day of February in the third year of Han Yonghe (AD 138), the dragon on the west side of the seismograph suddenly spit out copper balls, but the people in Luoyang did not feel the earthquake at all.A few days later, someone from Longxi (now southeastern Gansu) flew a horse to report an earthquake, and the time and direction were consistent with the seismograph, which showed the reliability and practicability of the seismograph.

In addition, Zhang Heng is proficient in mathematics.He conducted research on pi and gave two values ​​of pi, one is 730/232, which is approximately equal to 3.1466; Cui Yuan, who was a contemporary of Zhang Heng, once commented that he was "poor in math skills, but good at making good fortune" ("Book of the Later Han Dynasty Zhang Heng Biography"), which aptly summed up Zhang Heng's talent in science and technology.In order to commemorate Zhang Heng's outstanding contribution in science and technology, the international astronomy community named a crater on the back of the moon "Zhang Heng Crater".