《汉书·传·贾谊传》
水受热上蒸为云，云受冷又从天而降为雨，事物的变化自然现象错综复杂无法分清。
云烝雨降，纠错相纷。
When water is heated, it rises up as clouds, and when it cools, it falls from the sky as rain. The changes in the natural phenomena of things are too complicated to distinguish.