Yisizhan 乙巳占

Yisizhan 乙巳占 is a book on astronomy and divination written during the Tang period 唐 (618-907) by Li Chunfeng 李淳風 (602-670) from Yongxian 雍縣 in the prefecture of Qizhou 岐州 (today's Fengxiang 鳳翔, Shaanxi). He was gentleman for court discussion (chaoyilang 朝議郎), Director of the Imperial Archive (mMige langzhong 秘閣郎中), erudite in the Office of Imperial Sacrifices (taichang boshi 太常博士) and Grand Astrologer (taishi ling 太史令). For his merits in the compilation of the dynastic history, he was awarded with the title of Baron of Changle District 昌樂縣男爵. Li is known for his astronomical disputes with Fu Renjun 傅仁均 and his creation of an armillary sphere (huntianyi 渾天儀) with rings for the celestial equator (chidao 赤道), the ecliptic of the moon (baidao 白道), and that of the sun (huangdao 黃道). He wrote the books Faxiangzhi 法象志, Tuibeitu 推背圖, Dianzhang wenwu zhi 典章文物志, Ganyingjing 感應經 and Migelu 秘閣錄, the two treatises on astronomy (Tianwen zhi 天文志) in the official dynastic histories Jinshu 晉書 and Suishu 隋書, and developed the Linde Calendar (Linde li 麟德曆).

The book Yisizhan, with a length of 10 juan and finished around 656 CE, assembles statements and theories from astrological (xinzhan 星占) texts from before the Tang period and is thus a very rare collection of early astrology. Apart from astrology, Li's book also discusses astronomy and meteorological issues. Among the latter, the introduction of grades of wind speed or storm force is of particular interest. The eight grades range from the movement of tree leaves and the noise of cracking twigs to the uprooting of whole trees with their roots. Li also relates the wind direction with the Celestial Stems and Terrestrial Branches and the trigrams of the Yijing 易經 "Book of Changes", and thus goes over from scientific modes to the divinatory one, namely "prognostication by wind" (fengzhan 占風). To determine the direction of winds, Li constructed weather vanes of chicken feathers and of wood.

The text is found in the series Shiwanjuanlou congshu 十萬卷樓叢書, Congshu jicheng chubian 叢書集成初編 and Xuxiu siku quanshu 續修四庫全書.