《汉书·志·天文志》
若雾非雾，沾衣不湿的云气，如出现则那个城市有披甲上阵而疾行军的情况。
若雾非雾，衣冠不濡，见则其城被甲而趋。
As if mist but not mist, clouds that cling to clothes without wetting them, when they appear, it is a sign of a sudden military advance on that city.