《黄帝内经·素问·六微旨大论》
岐伯说：天气居于上位，地气居于下位，上下交互于气交之中，为人类所居之处。
岐伯曰：上下之位，气交之中，人之居也。
Qi Bo said: Weather qi resides in the upper position, earth qi resides in the lower position, the top and bottom meet and exchange in qi exchange, which is where humans reside.