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
Zhou Dunyi that "the many are ultimately one and the one is ultimate." This was the first 11th-century Chinese text to argue for the inseparability of metaphysics or cosmology and ethics, as well as the first major Chinese text to explore the concept of the taijitu or "yin-yang symbol". It contained his theory of creation, which can be summarized in the following paraphrase of its first section: "In the beginning, there was t'ai chi (taiji) (the great ultimate of being), which was fundamentally identical with wu chi (wuji) (the ultimate of non-being). Because of the abundance of energy within t'ai chi, it