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?_ A. Because _any covering_ prevents the _radiation of heat from the tree_; and if the tree be _not cooled down by radiation_, the vapour of the air will _not be frozen_ as it comes in contact with it. Q. _Why is the BASS or CANVASS itself (which covers the tree) always DRENCHED with DEW?_ A. The bass or canvass covering _radiates heat_ both _upwards and downwards_; and is, therefore, _so cooled down_, that it readily _chills all the vapour of the air_ (which passes over it) _into dew_. Q. _Why does SNOW at the foot of a HEDGE or WALL melt sooner, than in an open field?_ A. Because the hedge or wall _radiates heat into the snow beneath_, which melts it. Q. _Why is there NO DEW after a WINDY NIGHT?_ A. 1st--Because the wind _evaporates the moisture_, as fast as it is deposited; and 2ndly--It _disturbs the radiation of heat_, and diminishes the deposition of dew thereby. Q. _Why are VALLEYS & HOLLOWS often thickly covered with DEW, although they are sheltered?_ 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.