The Qinlüshuo 琴律說 "Explanations to the Modulation of the Zither"
is a book on musical temperation written by the grand Neo-Confucian master Zhu Xi 朱熹 during the Southern Song period. The book is included in Zhu Xi's collected writings Zhu Wengong wenji 朱文公文集, in the books Shenglü tongkao 聲律通考 and Qinshu daquan 琴書大全, and in the reprint series Sibu congkan 四部叢刊. A modern edition is to be found in the collection Qinqu jicheng 琴曲集成.
Zhu Xi's text is important for the history of the qin zither as well as for acoustics theory. The musicological part is based on Shen Kuo's 沈括 texts Shisan fan yun 十三泛韻 and Ziran zhi jie 自然之節, and for its own part influenced writings on the qin zither, like Xu Li's 徐理 Qintong 琴統 from the late Southern Song period, particularly the chapter on the "ten rules" (shi ze 十則), in which the technique to tune the strings of a zither is explained. Zhu Xi's explanation of tuning follows the old method of alternatively adding and subtracting a third of the length of a pitchpipe or a string, to create the next higher tone of a gamut. Yet some of his statements have been copied from older, erratic texts, and are barely practicable. He mixed up, for instance, the chunlü method 純律 ("pure intonation") with the sanfen method 三分律 ("three-tone temperament"). His book is nevertheless of great help to understand the theory of the qin zither in ancient China.
Source: Yu Hui 喻輝 (1996). "Qinlüshuo 琴律說", in: Zhongguo xueshu mingzhu tiyao 中國學術名著提要, Yishu 藝術卷, Shanghai: Fudan daxue chubanshe, p. 84.