They are probably kept near to the surface of the earth by a superstratum of cold air. A cold air lying above, or a cold air lying below, might equally contribute to keep a fog near the surface of a particular part of the earth, until a flow of wind, or a fall of rain, altered the atmospheric condition.
"He bindeth up the waters in his thick clouds; and the cloud is not rent under them."—Job xxvi.
There are many interesting facts connected with the history of dew. It has attracted the attention of natural philosophers in all ages. But its true theory was never understood until recently. The ancients imagined that dews were shed from the stars; and the alchemists and physicians of the middle ages believed that the dew distilled by night possessed penetrating and wonder-working powers. The ladies of those times sought to preserve their beauty by washing in dew, which they regarded as a "celestial wash." They collected it by placing upon the grass heaps of wool, upon the threads of which the magic drops clustered.
CHAPTER XVIII.
Clouds are volumes of vapour, usually elevated to a considerable height.