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
Yang Yin Emperor Xiaozhuang. However, after Yuan Hao was subsequently defeated by Erzhu, permitting Emperor Xiaozhuang to return to Luoyang, Yang Yin believed that the empire was not yet at peace and decided to leave governmental service, taking up a hermit's existence with his friend Xing Shao at Mount Song. Thereafter, however, Yang Yin's cousin Yang Youqing, while advising Emperor Xiaowu, whom Gao Huan had made emperor, used strong language that offended Emperor Xiaowu and was put to death. Another member of Gao's staff, Guo Xiu, was jealous of Yang's abilities, and he therefore gave Yang false news that Gao was intending