Chinese sun and moon mirrors being hung round the neck, or because necks are concave things. Liu An's (c. 139 BCE) "Huainanzi" "Masters of Huainan", which is a compendium of writings from various schools of Chinese philosophy, was the first text to record "fangzhu" dew-collectors. Two "Huainanzi" chapters metaphorically use "sun and moon mirrors" to exemplify "yang" and "yin" categories and elucidate the Chinese notion of "ganying" "cosmic resonance" through which categorically identical things mutually resonate and influence each other. The "yángsuì" 陽燧 "burning-mirror" is "yang", round, and sun-like; the "fāngzhū" 方諸 "square receptacle" is "yin", square, and moon-like. The first context describes "yangsui" and
Taijitu the "yin and yang symbol", itself popularly called "taijitu", represents the second of these five parts of the diagram. The term "taijitu" in modern Chinese is commonly used to mean the simple "divided circle" form (), but it may refer to any of several schematic diagrams that contain at least one circle with an inner pattern of symmetry representing yin and yang. While the concept of yin and yang dates to Chinese antiquity, the interest in "diagrams" (圖 "tú") is an intellectual fashion of Neo-Confucianism during the Song period (11th century), and it declined again in the Ming period, by