(劉歆; c. 50 BCE – 23 CE), courtesy name
(子駿), was a Chinese astronomer, mathematician, historian, librarian and politician during the
(9 – 23 CE). He later changed his name to
. He was the son of Confucian scholar
(77 – 6 BCE) and an associate of other prominent thinkers such as the philosopher
(c. 43 BCE – 28 CE). Liu founded the Old Text school of Confucianism.
Early life
Liu Xin was the son of Confucian scholar Liu Xiang (77 – 6 BCE). Liu was a distant relative of Liu Bang, the founder of the Han dynasty, and was thus a member of the ruling dynastic clan (the Liu family). Liu Xin's paternal grandfather ranked as a marquess.
Librarian
As a curator of the imperial library he was the first to establish a library classification system and the first book notation system. At this time the library catalog was written on scrolls of fine silk and stored in silk bags.
As the imperial librarian, Liu Xin both catalogued and annotated or edited ancient texts. These projects of his produced what became definitive texts of a number of orthodox canons of Chinese philosophy and history. However, since the 19th and early 20th centuries, antiquarians and historians have accused Liu of excessive editing, to the point of falsifying historical texts. These criticisms were systematically analysed by the Doubting Antiquity School of historians. According to the general theory of this school of history, Liu edited ancient texts for political purposes. He edited accounts of ancient historical events, and inserted into the legendary lineage of ancient rulers figures or relationships that were either invented, or borrowed from separate legends. In this way, he created a narrative of ancient rulers and successive dynasties which satisfied the "succession of five elements" theory. According to this theory, each ruler and/or dynasty represented one of the five traditional Chinese elements, and the mandate of Heaven rotated between the elements. The account edited by Liu would satisfactorily explain the rule of the Han Dynasty (and/or the brief Xin Dynasty that overthrew it) in terms of the elements they were said to represent. Further, according to this theory, the account edited by Liu also conveniently showed a series of successions between various claimed ancestors of the Han and Xin houses. As the imperial librarian, Liu was able to set the definitive text of these ancient texts, and expunge earlier versions. The Doubting Antiquity School drew evidence from discrepancies between the texts edited by Liu and earlier or contemporaneous texts. For example, figures or events appearing in Liu's edited versions did not appear in earlier or contemporaneous texts. In some cases, Liu's text referred to a supposed earlier source that was not mentioned in any other texts. Although Liu has been vindicated in respect of some of these issues by later archaeological discoveries of older manuscript that corroborated Liu's version, some other criticisms have become largely accepted by historians.
Calculation of pi
For centuries before the reign of Wang Mang (r. 9–23) the Chinese had used the value of 3 for their calculation of pi, the ratio of a circle's circumference to its diameter (now known to be approximately equal to 3.14159). Between the years 1 and 5, while working for the de facto head of state Wang Mang, Liu Xin was the first to give a geometrical figure which implies the improved approximation π ≈ 3.1547, although the exact method he used to reach this figure is unknown. However, the ancient record of Liu Xin's 'Jia Liang Hu' standard is still preserved in Beijing, which Joseph Needham quotes below with modern references for archaic units (Wade-Giles spelling):
The standardised chia liang hu (has) a square with each side 1 chhih (foot) long, and outside it a circle. The distance from each corner of the square to the circle (thiao phang) is 9 li 5 hao. The area of the circle (mu) is 162 (square) tshun (inches), the depth 1 chhih (foot), and the volume (of the whole) 1620 (cubic) tshun (inches).
Later mathematicians such as Zhang Heng (78–139) and Liu Hui (fl. 3rd century) would improve Liu's calculation for pi.
Death
Although Liu Xin was originally a loyal partisan of Wang Mang, after Wang's troops suffered defeat on July 7, 23 at the Battle of Kunyang, Liu Xin plotted with others to overthrow Wang Mang. The plot was discovered, and all the conspirators committed suicide or were executed.
Astronomy
A crater on Mars was named in his honor.
劉歆（前50年？ - 23年），字子駿，改名劉秀，漢朝宗室，西漢末年及新朝官員及重要學者，協助王莽篡位，出任新朝高職「羲和官」，號稱國師，晚年卻因兒子被殺與誤信預言，謀叛事敗自殺。劉歆博覽圖書，精通經學，提倡古文經學，推動把《左傳》及《古文尚書》等古文經列於學官，引發漢代今古文經學之爭；他曾與父親劉向一同校閱宮庭藏書，編成目錄學的重要著作《七略》及《別錄》，反映當時的學術思想流派。