terça-feira, 14 de junho de 2011

Shen Kuo 沈括

While Europe was in the core of the Middle Ages, the Song dynasty (960-1279 A.D.) ruled over an empire that extended from the Pacific Ocean to almost the eastern border of Tibet. This dynasty fell in 1279 attacked by the Mongols of Kublai Khan, who initiated the Yuan dynasty.

When Shen Kuo (1031-1095 A.D.) was born the Song dynasty was at his peak and commerce as well as culture was flourishing: Song’s poems are among the most beautiful in Chinese literature. Shen Kuo is known to have written some poems; this shall not surprise, as, at that time, and for many years later, the Chinese examination to become a government official required, among other things, the mastering of qualities such as poem writing or calligraphy drawing.

Shen Kuo was the son of a civil officer and, starting from childhood, had the chance to travel with his father around the country and to observe him working. He learned many skills he would need afterwards, when he would become an officer himself at the age of 23, after his father’s death. The tasks of a civil officer were very varied including the control of the agriculture’s efficiency, supervising the construction of public works and monitoring waterways: he distinguished himself for his ability, right from the beginning, improving agriculture in the region that had been assigned to him by building drains and embankments that made new lands fertile. After this first success he was assigned more important charges, but the real change was in 1068. That year Shen Song became the new emperor, and among his newly appointed counselors was Shen’s family friend Wang An Shi, who started a reform program and called Shen to work at the court in the capital Kai Feng.

When a new emperor settled, the costume was to enforce a new calendar and, in 1072, Shen was given this task, being appointed Director of the Imperial Department of Astronomy: he set a program of five years daily observation and record of the stars position in order to accomplish his job. However, not all the astronomers working with him were skillful enough and he caught some of them falsifying data: the calendar came into use but was not as good as it could have been.

Assigned to other tasks he always distinguished himself for his outstanding ability in military strategy, international diplomacy (solving a crisis with northern population willing to invade the country), economy understanding (he wrote essays on market intervention as well as on supply and demand). But after 1077 his career had a sudden halt: his patron Wang An Shi had reformed and he found himself attacked by Wang’s political opponents. He was still assigned some tasks but his enemies managed to have him banished. After that he lived for six years practically under house arrest, until he was granted pardon and moved to his beautiful property (which he named Dream Pool) in Jiang Su province, where he spent the rest of his life. During all the time after the end of his public career he devoted himself to science and wrote many essays. Among these there is the remarkable Dream Pool Essay (or more literally “Dream Pool Brush Talk”, title he gave referring to the solitude in which he spent his last years, as he says: “I have only my writing brush and ink slab to converse with”), an essay about his work on many different topics, such as mathematics, cartography, astronomy, geology, music and many others, containing accurate descriptions of new techniques he had the change to observe and study during his many years of service around the country. This is very important because it was not infrequent at the time for artisans and technicians to be illiterate or at least incapable of writing about their craft with a satisfactory description.

He extensively wrote about the movable type printing invented by Bi Sheng (990–1051 A.D.) and his work was a valuable source for Wang Zhen when he invented wooden movable type printing in 1298 and for Hua Sui who innovated movable type printing in 1490.

In this book (and in the following ones) we can find the theories he developed in many years of work; among these the most remarkable is his study on compasses. In the book we can find the first description (in the world) of the magnetic needle compass as well as the statement of magnetic declination (about a century earlier that in Europe), when Shen observes that a needle rubbed with a loadstone points south (*) “but it always inclines slightly to the East” .

Also, from the observation of fossils of sea creatures far from the sea he understood that what at his time was an inland mountain must have been in the past a sea shore; seeing petrified bamboos where the habitat would not support bamboo growth, he elaborated a theory about gradual climate changes.

When working in mathematics, he tended to have a more abstract approach than most Chinese mathematicians: he liked to look at problems just for their own sake, regardless of their applications. Among these, he faced the problem of writing large numbers (that he obtained as solutions of his problems) in the Chinese character-based numeric system, where the maximum number is 10.000 (wan). For example to express the number 10^172 he had no other chance than to write wan wan… wan 43 times (or at least we think he did, as there are discrepancies on the number of wan’s in different manuscripts, probably due to errors of the copyists).

Having been head of the Astronomy Imperial Department for some years, astronomy is one of the fields in which his contribution is greater: he collected data to support Zhang Heng theory that the Moon was reflecting rather than emitting light, he tried to explain the periods of retrograde motion of planets conjecturing a willow leaf motion composed with circular motion (epicycles), he improved astronomical instruments such as the gnomon and the armillary sphere, he measured the movement of the polestar over time, etc.

In the West, Shen Kuo’s work did not fully spread until the 1950s, when the British biochemist and sinologist historian Joseph Needham wrote “The Science and Civilization in China”. This book is even now one of the main references about Shen Kuo’s work in a western language.

Caterina Umiltà

(*) The Chinese name for compass is “nan zheng”, which literally means “south needle”.

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