Xin yixang fa yao 新儀象法要

Xin yixang fa yao 新儀象法要 "Essentials of the new armillary sphere" is a book on the design and function of a novel, water-powered armillary sphere written by the astronomer Su Song 蘇頌 (1020–1101) during the Northern Song period 南宋 (1127-1279). Su Song, courtesy name Zirong 子容, hailed from Jinjiang 晉江 (today part of Quanzhou 泉州, Fujian), and later moved to Danyang 丹陽, Jiangsu. He obtained the jinshi degree in 1042 and was Minister of Personnel (libu shangshu 吏部尚書) and Counsellor-in-chief (zaixiang 宰相).

The book of 3 juan length was completed between 1094 and 1096. It is also known with the titles Shaosheng xiangyi fayao 紹聖儀象法要 or Xiangyi fazuan 儀象法纂. The oldest surviving print, produced by Shi Yuan 施元, dates from 1172, and is a kind of critical edition based on at least two circulating versions of Su's text. The most important edition is found in the series Shoushange congshu 守山閣叢書 and the Congshu jicheng chubian 叢書集成初編.

This book is the earliest known monograph on a hydraulic-powered astronomical instrument in China. It reflects the level of Chinese astronomy and mechanical engineering in the 11th century. The astronomical observatory combines an armillary sphere, a celestial globe, and a timekeeping device, all driven by hydraulic power. The observatory was divided into three levels: the armillary sphere placed on the top, the celestial globe in the middle, and the timekeeper at the bottom. When the time was right, the timekeeper announced the positions of the stars, which corresponded to the actual celestial phenomena.

Images 1-4. Illustrations from the Xin yixang fa yao 新儀象法要

Armillary sphere (right) and celestial globe (left).

General view (right) and mechanism (left) of the astronomical tower.

The book starts with a dedication written by Su titled Jin yixiang zhuang 進儀象狀. It reports on the origin, process of construction, and the characteristics of the water-powered armillary sphere, especially in comparison to similar instruments from previous eras. The main body of the text is primarily composed of diagrams, introducing the overall structure and individual components of the armillary sphere. Each diagram is accompanied by a textual description. The first fascicle focuses on the armillary sphere (hunyi 渾儀), featuring seventeen different diagrams. The middle part introduces the celestial globe (hunxiang 渾象). In addition to five structural diagrams, there are also two star maps presented in five illustrations, as well as nine types of star maps showing the positions of stars during twilight at different seasons. The last chapter focuses on the overall structure of the new water-powered armillary sphere tower, including the primary and secondary mechanisms within the tower (yixiangtai 儀象臺), as well as the time-reporting apparatus. This section includes a total of twenty-three diagrams, along with four additional diagrams detailing alternative construction methods. There is one section for which no image is provided (Yixiang yunshui fa 儀象運水法 "Using water to power the armillary sphere").

The total number of diagrams and illustrations is 60. These structural diagrams are the oldest known mechanical drawings in China. They use perspective and schematic techniques, along with labelled names, to depict the various mechanical components. Through restoration studies, it has been proven that every line and detail in these drawings is based on precise calculations and accurately corresponds to the dimensions and measurements recorded in the book. Su Song's book reveals that the crucial component of modern mechanical clocks—the anchor escapement (modern Ch. miaozhuang qinzong qi 錨狀擒縱器)—was a Chinese invention.