《礼记·月令》
命令主管官吏说： 天气上升 地气下降，天地不通，闭塞而成冬天。 
命有司曰：天气上腾，地气下降，天地不通，闭塞而成冬。
He ordered the chief officials and said, "The weather is ascending, and the subterranean vapors are descending. Heaven and earth are not connected and become shut off, so it becomes winter."