Sochushi

A mathematician and calendar scholar from the Northern and Southern Dynasties of China. He was born in Fanyang (now Zhuo County, Hebei Province). His courtesy name was Wenyuan. He served Emperor Xiaowu of the Southern Song Dynasty as Grand Historian. His mathematical achievements include the work "Zhujutsu". This book has not been handed down to the present day, but it is recorded in the "Luyue Zhi" section of the "Suishu", which says that the content was so difficult that no one studied it, and it gradually fell out of use. Also, according to the "Suishu", this book contains a study of pi, in which Zu Chongzhi calculated 3.1415926 < pi < 3.1415927, giving pi = 22/7 as the approximate ratio and pi = 355/113 as the density. This density was not discovered in Europe until the 16th century. He is also known to have commented on "Nine Chapters of Mathematics" and "Haidao Sanjing."

One of his achievements in the field of calendar science was the creation of the "Da Ming Calendar." This took precession into account, and was submitted to the government in 462, but was not used after the death of Emperor Xiaowu. Later, during the Tianjian period of the Liang Dynasty (502-519), thanks to the efforts of Zu Chongzhi's son Zu Zhi (date of birth and death unknown), the superiority of this calendar was recognized, and it was adopted as the official calendar. He was also blessed with a talent for making machines, and improved on the existing south-pointing wheel, and built water-powered mortars and ships such as paddle steamers.

His son, Zuzhi, was also an excellent mathematician. His pen name was Jingshuo. He worked with his father to make machines and to promote the adoption of his father's Great Ming Calendar. In mathematics, he made a great contribution to the method of correctly calculating the volume of a sphere.

[Shinichi Oya]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

中国、南北朝時代の数学者、暦学者。范陽(はんよう)（現、河北(かほく)省涿(たく)県）の出身。字(あざな)は文遠。南朝宋(そう)の孝武帝に仕えて太史令となった。数学上の業績としては『綴術(てつじゅつ)』の著作がある。この書は、今日に伝わっていないが、『隋書(ずいしょ)』の「律暦志」に記録があり、それによれば内容が難解なために学習する者がなく、いつのまにか使われなくなったという。また『隋書』によれば、この書に円周率の研究があり、祖沖之は3.1415926＜π＜3.1415927を計算し、約率としてπ=22／7、密率としてπ＝355／113を与えている。この密率はヨーロッパでは16世紀になって発見されたものである。このほか彼は『九章算術』『海島算経』の注釈を行ったことが知られている。

　暦学の分野での業績としては『大明暦』をつくったことがあげられる。これは歳差も考慮されたもので、462年に上申されたが孝武帝の死去により用いられず、後年、梁(りょう)の天監年間（502～519）になって、祖沖之の子の祖之(けんし)（生没年不詳）の努力によってその優れた点が認められ、官暦に採用された。また彼は機械製作の才能にも恵まれており、従来からあった指南車を改良したり、水力で動かす臼(うす)や外輪船のような船なども製作した。

　なお、子の祖之も優れた数学者であった。字を景爍(けいしゃく)といい、父とともに機械をつくり、父の『大明暦』の採用に力を尽くした。数学では球の体積を正しく求める方法に業績を残している。

［大矢真一］

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