“When rain falls from the upper region of the air, we observe at a considerable altitude a thin light veil, or a hazy turbidness; as this increases, the lower clouds become diffused in it, and form a uniform sheet. Such is the stratus cloud described by Dante ( V 115) as covering the valley from Pratomagno to the ridge on the opposite side above Camaldoli. This cloud is a widely extended horizontal sheet of vapor, increasing from below, and lying on or near the earth’s surface. It is properly the cloud of night, and first appears about sunset, usually in autumn; it comprehends creeping mists and fogs which ascend from the bottom of valleys, and from the surface of lakes and rivers, in consequence of air colder than that of the surface descending and mingling with it, and from the air over the adjacent land cooling down more rapidly than that over the water, from which increased evaporation is taking place,”

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