Feiyin yuzhi lu 費隱與知錄

Feiyin yuzhi lu 費隱與知錄 is a book on natural sciences written during the late Qing period by Zheng Fuguang 鄭復光 (1780–1853), courtesy name Yuanfu 元甫, style Huanxiang 浣香 (also written 澣香 or 香薌). It was published in 1842. The title is derived from a sentence in the Classic Zhongyong 中庸 which says that “the way of the superior man reaches far and is secret, but common, ignorant men and women may intermeddle with the knowledge of it” (Junren zhi dao fei er yin. Fufu zhi yu, ke yi yu zhi yan 君之道費而隱。夫婦之愚，可以與知焉。 Trans. Legge xxx). Zheng never obtained a state office, but travelled a lot and discussed with knowledgeable scholars of the time like Wang Lai 汪萊 (1768–1813), Li Rui 李銳 (1769–1817) or Bao Shichen 包世臣 (1775–1855). Zheng also wrote a book on optics, Jingjing lingchi 鏡鏡詅癡, as well as the books Zhoubi suanjing qianzhu 周髀算經淺注 , Bisuan shuolüe 筆算說略, Chousuan shuolüe 籌算說略, Zheng Yuanfu zhaji 鄭元甫札記, and Zheng Huanxiang yigao 鄭浣香遺稿. The book of 2 juan length adopts a question-and-answer format, bringing together general knowledge from China and the West to address some of the queries in nature and daily life. There are 225 brief chapters on geography, physics, meteorology, astronomy, biology, chemistry and medicine. About one tenth of the book deals with optics, and can be seen as a supplement to the Jingjing lingchi. Zheng describes the pinhole imagining, explaining that when the screen is very close to the pinhole, an upright image is formed on the screen; as the distance increases, the image becomes blurry and disappears; when it is farther away, an inverted image appears. The author believes that 'light transmission is like heat transmission' (tou guang ji ru tou huo 透光即如透火). He explains heat transfer through 'ventilation' (touqi 透气 ; convection) and 'conductance' (ge wu zi sheng 隔物自生, conduction), such as 'boiling water in a pot; if the pot is hot, the water will boil.' It also notes that black substances have the strongest ability to absorb heat radiation: 'when fire receives light, not only does paper and coal dry out and catch fire, but light in dark places is even more intense.' Conversely, white substances have the weakest ability to absorb heat radiation: 'only white paper receives light but cannot get the heat from it.' (du bai zhi cheng guang, jing bu de guang 独白纸承光，竟不得光). In the field of fluid mechanics, the book also elaborates on the law of buoyancy introduced by Western missionaries and explores the relationship between buoyancy and specific gravity. It explains the principle of water absorption in siphons and provides a detailed explanation of the working principles of the ancient 'guoshanlong' 过山龙 machine used for drawing water with fire tickets 火票 and the 'cupping therapy' (拔火罐) used in traditional Chinese medicine. A part of the book is also dedicated to agriculture and metereological phaenomena. Rain is explained as the evaporation of water due to heat and its condensation when it encounters cold air. Zheng thus criticized the superstitious belief in 'dragons bringing rain.' He asserted that 'lightning strikes' 雷击 are the result of 'interaction of air currents, 气类相感' criticizing the traditional concept of Thunder God and Lightning Mother. 雷公电母" Zheng’s theory of the compass needle is influenced by the teachings of the Jesuit Father Ferdinand Verbiest (Nan Huairen 南怀仁), found in his book Lingtai yixiang zhi 灵台仪象志. Zheng also mentions the Western concept of the four elements (sixing shuo 四行说)