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
Yin and yang word "yang" "sunny side" and a few contain "yin" "shady side". In China, as elsewhere in the Northern Hemisphere, sunlight comes predominantly from the south, and thus the south face of a mountain or the north bank of a river will receive more direct sunlight than the opposite side. "Yang" refers to the "south side of a hill" in Hengyang 衡陽, which is south of Mount Heng 衡山 in Hunan province, and to the "north bank of a river" in Luoyang 洛陽, which is located north of the Luo River 洛河 in Henan. Similarly, "yin" refers to "north side of