A. The surrounding hills prevent the repose of air (in the valleys) from being disturbed; but do not overhang and screen them, so as to arrest their radiation.
Q. Why does dew fall more abundantly on some things than upon others?
A. Because some things radiate heat more freely than others, and therefore become much cooler in the night.
Q. Why are things which radiate heat most freely, always the most thickly covered with dew?
A. Because the vapour of the air is chilled into dew, the moment it comes in contact with them.
Q. What kind of things radiate heat most freely?
A. Grass, wood, and the leaves of plants, radiate heat very freely: but polished metal, smooth stones, and woollen cloth, part with their heat very tardily.
Q. Do the leaves of all plants radiate heat equally well?
A. No. Rough woolly leaves (like those of a holly-hock) radiate heat much more freely, than the hard smooth polished leaves of a common laurel.