Liu Xin (Chinese: 劉歆; Wade–Giles: Liu Hsin) (ca. 50 BC – AD 23), later changed name to Liu Xiu (Chinese: 劉秀; pinyin: Liú Xiù), courtesy name Zijun (Chinese: 子駿; pinyin: Zǐjùn), was a Chinese astronomer, historian, and editor during the Western Han Dynasty (206 BC-AD 9) and Xin Dynasty (AD 9–23). He was the son of Confucian scholar Liu Xiang (77–6 BC) and an associate of other prominent thinkers such as the philosopher Huan Tan (d. 28 AD). Liu founded the Old Text school of Confucianism.
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.
Calculation of pi (π)
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 a more accurate value of pi at 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' 嘉量斛 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).
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.
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