A Guide To The Scientific Knowledge Of Things Familiar Part 47

A. Yes; and was, therefore, a plain _demonstration of the power of G.o.d_, who could change the very _nature of things_ at his will.

Q. _Why do our CLOTHES FEEL DAMP, after walking in a fine evening in SPRING or AUTUMN?_

A. Because the vapour (_condensed by the cold earth_) lights upon them, like dew.

Q. _Why are WINDOWS often covered with thick MIST, and the frames wet with standing WATER?_

A. The temperature of the _external air_ always _falls at sun-set_, and _chills the window-gla.s.s_, with which it comes in contact.

Q. _How does this account for the MIST and WATER on a WINDOW?_

A. As the warm vapour of the room _touches the cold gla.s.s_, it is _chilled_ and _condensed into mist_; and the mist (collecting into drops) _rolls down the window-frame_ in little streams of water.

Q. _Does the GLa.s.s of a window COOL down more RAPIDLY than the AIR of the room itself?_

A. Yes; because the air is _kept warm by fires_, and the _animal heat_ of the people in the room; in consequence of which, the _air of a room suffers very little diminution of heat_ from the setting of the sun.

Q. _Whence arises the VAPOUR of a ROOM?_

A. 1st--The very _air_ of the room _contains vapour_:

2ndly--The _breath_ and _insensible perspiration_ of the inmates _increase_ this vapour: and

3rdly--_Hot dinners_, the _steam of tea_, &c. contribute to _increase it still more_.

Q. _What is meant by "the INSENSIBLE PERSPIRATION?"_

A. From every part of the human body an _insensible and invisible perspiration issues_ all night and day; not only in the hot weather of _summer_, but also in the coldest day of _winter_.

Q. _If the perspiration be both INSENSIBLE and INVISIBLE, how is it KNOWN that there IS any such perspiration?_

A. If you put your naked arm _into a clean dry gla.s.s cylinder_, the _perspiration_ of your arm will soon _condense_ on the gla.s.s, like mist.

Q. _Why are CARRIAGE WINDOWS very SOON covered with thick MIST?_

A. The warm vapour of the carriage _is condensed the moment it touches the cold gla.s.s_, and covers it over with a thick mist.

Q. _Why is the gla.s.s window COLD enough to condense the vapour of the carriage?_

A. Because the _inside_ of the carriage is much _warmer_ than the _outside_, and the gla.s.s window is made cold by contact with the _external air_.

Q. _Where does the WARM vapour of the carriage come from?_

A. The warm _breath_ and _insensible perspiration_ of the persons riding in the carriage, load the air of it with warm vapour.

Q. _What is the cause of the pretty FROST-WORK seen on bed-room WINDOWS in winter-time?_

A. The _breath_ and _insensible perspiration_ of the sleeper (coming in contact with the ice-cold window) is _frozen_ by the cold gla.s.s, and forms those beautiful appearances seen in our bed-rooms in a winter morning.

Q. _Why is the GLa.s.s of a window colder than the WALLS of a room?_

A. Gla.s.s is a very _excellent radiator_; and, therefore, most _rapidly parts with its heat_.

Q. _Why is a TUMBLER of cold WATER made quite DULL with mist, when brought into a room FULL of PEOPLE?_

A. Because the _hot vapour of the room_ (coming in contact with the cold tumbler) _is condensed upon it_; and changes its invisible and gaseous form for that of a _thick mist_.

Q. _Why is a GLa.s.s made quite DULL, by laying a HOT HAND upon it?_

A. The _insensible perspiration_ of the hot hand is _condensed_ upon the cold gla.s.s, and thus made perceptible.

Q. _Why are WINE-GLa.s.sES made quite DULL when they are brought into a room FULL of COMPANY?_

A. The _hot vapour of the room_ (coming in contact with the cold wine-gla.s.ses) _is condensed_ upon them, and covers them with vapour like dew.

Q. _Why does this misty appearance GO OFF after a little time?_

A. Because the gla.s.s becomes of the _same temperature_ as the _air of the room_, and will no longer _chill the vapour_ which touches it, and _condense it into mist_.

Q. _Why is a WINE-GLa.s.s (brought out of a CELLAR into the AIR) covered with a thick MIST in summer-time?_

A. The vapour of the hot air is _condensed_ by the cold gla.s.s, and covers it as a thick mist.

Q. _Why does BREATHING on a GLa.s.s make it quite DULL?_

A. Because the hot breath is _condensed_ by the cold gla.s.s; and, therefore, covers it with a thick mist.

Q. _Why do WALLS stand thick with WET in a sudden THAW?_

A. The walls (being thick) cannot _change their temperature so fast_ as the thin air can; and, therefore, they _retain their cold_ after the thaw has set in.