A Guide To The Scientific Knowledge Of Things Familiar - LightNovelsOnl.com
You're reading novel online at LightNovelsOnl.com. Please use the follow button to get notifications about your favorite novels and its latest chapters so you can come back anytime and won't miss anything.
Q. _How does RETAINING their COLD account for their being so WET?_
A. As the vapour of the warm air _touches the cold wall_, it is _chilled_ and _condensed into water_, which _sticks to the wall_, and sometimes trickles down in little streams.
Q. _Why does a thick WELL-BUILT HOUSE contract more DAMP of this kind, than an ORDINARY one?_
A. Because the walls are much _thicker_; and (if the frost has penetrated _far into the bricks_) it takes a long time to reduce them to the _same temperature as the air_.
Q. _Why are BANISTERS, &c. DAMP after a THAW?_
A. The wooden banister (being made of some very close-grained, varnished wood) cannot _change its temperature so fast_ as the air; and, therefore, _remains cold_ some time after the thaw has set in.
Q. _How does THIS account for the BANISTERS being DAMP?_
A. The vapour of the warm air (_coming in contact with the cold banister_) is _chilled_, and condensed into _water upon it_.
Q. _Why is our BREATH VISIBLE in WINTER and NOT in SUMMER?_
A. In _winter_ the coldness of the air condenses our breath into _visible vapour_; but in _summer_ the air is _not cold enough_ to condense it into visible vapour.
Q. _Why are our HAIR and the BRIM of our HAT often covered with little drops of pearly DEW in winter-time?_
A. The breath (issuing from our mouth and nose) _is condensed into drops_, as it comes in contact with our cold hair or hat; and (being condensed) hangs there in little dew-drops.
Q. _Why does the STEAM of a RAILWAY BOILER often pour down, like fine rain, when the steam is "let off?"_
A. The steam from the steam-pipe (when the air is cold) _is condensed by contact with the chill air_, and falls like fine rain.
Q. _Why is there LESS DEW when the WIND is EASTERLY, than when the wind is WESTERLY?_
A. _Easterly_ winds cross the _continent of Europe_, and, (as they pa.s.s over _land_) are _dry_ and _arid_; but _westerly_ winds cross the _Atlantic Ocean_; and (as they pa.s.s over _water_) are _moist_ and _full of vapour_.
Q. _How does the DRYNESS of an eastern wind PREVENT DEW-FALLS?_
A. As the easterly winds are _dry_, they _imbibe_ the moisture of the air; and, therefore, there _is very little_ left to be condensed into _dew_.
Q. _How does the MOISTNESS of a western wind PROMOTE dew-falls?_
A. As the westerly winds are _saturated with vapour_, they require a _very little reduction of heat_ to cause a _copious deposition of dew_.
Q. _When is DEW most COPIOUSLY distilled?_
A. After a hot day in summer or autumn, with the _wind in the west_.
Q. _Why is DEW distilled most COPIOUSLY after a HOT day?_
A. Because the surface of the earth _radiates_ heat very freely at sunset; and (becoming thus _much colder than the air_) _chills its vapour_, and condenses it into dew.
Q. _Does not AIR radiate heat, as well as the EARTH and its various plants?_
A. No. The air _never radiates heat_, nor is the air itself _made hot_ by the _rays of the sun_.
Q. _How is the AIR made HOT or COLD?_
A. By _convection of hot or cold currents_.
Q. _What is meant by "CONVECTION of hot and cold currents?"_
A. The air (which is heated by the surface of the earth) _ascends, warming the air_ through which it pa.s.ses. _Other_ air (being warmed in a similar way) _also ascends, carrying heat_; till _all the air_ is made hot.
Q. _Is the AIR made COLD in a similar way?_
A. Yes. The air resting on the earth is _made cold by contact_: this cold air makes the _air above it cold_; and cold currents or winds _shake the whole together_, till all becomes of one temperature.
Q. _Why is MEAT very subject to TAINT on a MOON-LIGHT night?_
A. In a bright moon-light night, _meat radiates heat very freely_; and is, therefore, soon _covered with dew_, which produces _rapid decomposition_.
Q. _Why do PLANTS GROW RAPIDLY in MOON-LIGHT nights?_
A. In bright moon-light nights _rapid radiation is carried on_, and _dew is plentifully deposited_ on young plants, which conduces much to their growth and vigour.
Q. _Why is evening DEW INJURIOUS to HEALTH?_
A. Because the condensed vapours are always laden with _noxious exhalations from the earth_: this is especially the case in _marshy_ countries.
Q. _Is HONEY-DEW a similar thing to DEW?_
A. No. Honey-dew is a sweet liquid _shed by a very small insect_ (called the aphis), and deposited in autumn _on the under surface_ of favourite leaves.
