Part 46 (1/2)
Q. _How can a thin covering of Ba.s.s 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 Ba.s.s or CANVa.s.s itself (which covers the tree) always DRENCHED with DEW?_
A. The ba.s.s or canva.s.s covering _radiates heat_ both _upwards and downwards_; and is, therefore, _so cooled down_, that it readily _chills all the vapour of the air_ (which pa.s.ses 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. Gra.s.s, 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.
Q. _Shew the WISDOM of G.o.d in making gra.s.s, the leaves of trees, and ALL VEGETABLES, EXCELLENT RADIATORS of heat._
A. As vegetables _require much moisture_, and would often perish without a plentiful deposit of dew, G.o.d wisely made them to _radiate heat freely_, so as to _chill the vapour_ (which touches them) _into dew_.