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Zu Chongzhi  |
| CCTV.COM 2002-03-28 11:03:16 |
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 The greatest undertaking in the 20th century is for men to leave their globe and land on the distant mysterious moon. People named a lunar crater at the back of the round moon Zu Chongzhi in commemoration of this Chinese scientist who made a lasting contribution to the world by his study of circle.
As a boy Zu Chongzhi loved science and assiduously studied works on astronomy and mathematics. He did not believe everything ancients said with a blind faith and dared to correct their mistakes. His diligence resulted in many inventions. He made reforms to the south－pointing carriage. Whichever way it moved the wooden human figure on it pointed always to the south. His inventions like double－shafted single－wheeled cart, hydraulic mill, and thousand－li boat played a great role in the production life of that time.
 His most outstanding achievement is the calculation of the ratio of the circumference of a circle to its diameter （pi）. "Zhou Bi", a mathematical classic of Eastern Jin Dynasty （317－420）, believes that the ratio of the circumference to the diameter was 3 to 1. Between the year 1 to 5 when Liu Xin made a standard measure called "jialianghu" he improved the ratio to 3.145. Liu Hui, a mathematician of the Three Kingdoms period, claimed that "3 to 1" was rather a ratio of the circumference of the inscribed hexagon with the diameter of the circle than a ratio of the circumference of the circle with the diameter. He discovered that the more sides a polygon had the closer its circumference was to that of a circle. Thus he initiated the method of cyclotumy and obtained the approximate value of pi to be 3.14. It was believed that Zu Chongzhi adopted his cyclotumy. He carved up the circumference again and again and made long and meticulous calculations and obtained the result that the value of pi was between 3.1415926 to 3.1415927. The fractional value 355/113 Zu Chongzhi calculated for pi is quite unique in the history of mathematics. Ancient Greek didn't accomplish it. The Indians had no knowledge in this field. The very mathematical Arabians weren't able to obtain this result. In Europe it was obtained 1,000 years later. Regretfully, Zu Chongzhi's method of calculation was lost. We only find some records about Zu Chongzhi in "History of the Sui Dynasty". It was according to the methods he used in calculating the pi value and the sphere volume that posterity was able to know and use the circle more accurately.
 Zu Chongzhi was also a distinguished astrologer. He spent 10 years in observing the gnomon of 8 "chi" and obtained a precession of the equinoxes of only one degree every 45 years and 11 months. It was an important reformation of the Chinese calendar. His other contribution was to define the cycle of Jupiter and Mercury. He also fixed the tropical years at 365.2428 days. This was the most accurate before the Song Dynasty （960－1279） and the most advanced for over 600 years.
History recorded Zu Chongzhi's scientific achievements. Scholars in the world today still hold him in great respect for his contributions in science.
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