A Guide To The Scientific Knowledge Of Things Familiar Part 91

Q. _Why does a FIDDLE-STRING give a musical sound?_

A. The bow drawn across the string _causes it to vibrate_, and this vibration of the string _sets in motion the sound-waves of the air_, and produces musical notes.

Q. _Why does a DRUM sound?_

A. The parchment head of the drum _vibrates_ from the blow of the drum-stick, and sets in motion the sound-waves of the air.

Q. _Why do MUSICAL GLa.s.sES give sounds?_

A. Because the gla.s.ses _vibrate_ as soon as they are struck, and set in motion the sound-waves of the air.

Q. _Why do FLUTES, &c. produce musical sounds?_

A. The breath of the performer causes the _air in the flute to vibrate_, and sets in motion the sound-waves of the air.

Q. _Why do PIANO-FORTES produce musical sounds?_

A. The _keys of the piano_ (being struck with the finger) lift up a little hammer which _knocks against a string_; and the vibration thus produced, sets in motion the sound-waves of the air.

Q. _Why are SOME notes Ba.s.s and some TREBLE?_

A. _Slow_ vibrations produce _ba.s.s or deep sounds_; whereas, _quick_ vibrations produce _shrill or treble sounds_.

Q. _Why is an instrument FLAT when the STRINGS are UNSTRUNG?_

A. Because the vibrations are _too slow_; in consequence of which, the sounds produced are not _shrill_ or _sharp_ enough.

Q. _Why can persons living a mile or two from_

_a town HEAR the BELLS of the town-church SOME TIMES, and not at OTHERS?_

A. Fogs, rain, and snow, obstruct the pa.s.sage of sound; but when the air is _cold and clear_, sound is propagated more easily.

Q. _Why can we NOT hear sounds (as distant church bells) in RAINY weather, so well as in FINE weather?_

A. Because the falling rain _interferes with the undulations of the sound-waves_, and breaks them up.

Q. _Why can we not hear sounds (as distant church bells) in SNOWY weather, so well as in FINE weather?_

A. Because the falling snow _interferes with the undulations of the sound-waves_, and stops their progress.

Q. _Why can we HEAR distant clocks MOST distinctly in CLEAR COLD weather?_

A. Because the air is most _uniform_ then: there are not _two currents of air_ (one up and one down) to interrupt the sound-waves.

Q. _Why can persons hear the VOICES of men in conversation for a MILE distant, near the POLES, in winter time?_

A. Because the air is very _cold and very clear_; in consequence of which, there are not _two currents of air_ (one up and one down) to interrupt the sound-waves.

Captain Ross heard the voices of his men in conversation, a mile and a half from the spot where they stood.

Q. _Why are not SOUNDS (such as distant church bells) heard so distinctly on a HOT DAY as in FROSTY weather?_

A. Because there are _two currents of air_; the current of _hot_ air _ascending from the earth_, and the current of _colder_ air _falling towards_ the earth; and these two currents _break up the sound-waves_.

Q. _Why can we not hear SOUNDS (such as distant clocks) so distinctly in a thick MIST or HAZE, as in a CLEAR night?_

A. Because the mist _diminishes the velocity_ of the sound-waves, and (by overburdening them with vapour) _limits their length_.

Q. _Why do we hear SOUNDS better by NIGHT than by DAY?_

A. 1st--Night air is _more uniform_, because the ascending currents of air (raised by the action of the sun's rays) _cease_ as the evening advances; and

2ndly--Night is more _still_ from the suspension of business, and the cessation of the hum of men.

Q. _How should PARt.i.tION WALLS be made to PREVENT the voices in adjoining rooms from being HEARD?_

A. The s.p.a.ce between the laths (or canva.s.s) should be filled with _shavings or saw-dust_; and then no sound would ever pa.s.s from one room to another.

Q. _Why would SHAVINGS or saw-dust PREVENT the transmission of sound from room to room?_

A. Because there would be _several different media_ for the sound to pa.s.s through: 1st--the air;

2ndly--the laths and paper;

3rdly--the saw-dust or shavings;

4thly--the air again: and every _variety_ diminishes the _strength of the sound-waves_.