Q. Why is there never much dew at the foot of walls and hedges?
A. 1st—Because the wall or hedge acts as a screen, to arrest the radiation of heat from the earth: and
2ndly—The wall or hedge also radiates some portion of heat towards the earth.
Q. How do these things prevent the deposition of dew?
A. As the ground (beneath a wall, tree, or hedge) is not cooled by the radiation of heat, it remains of the same temperature as the air above it; in consequence of which, the vapours of the air are not chilled by it into dew.
Q. Why is there little or no dew beneath a flower-awning, although that awning be open on all four sides?
A. 1st—Because the awning arrests the radiation of heat from the ground beneath: and
2ndly—It radiates some of its own heat downwards; in consequence of which, the ground beneath an awning is not sufficiently cooled down to chill the vapour of air into dew.
Q. How can a thin covering of bass or even muslin protect trees from frost?