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 PARTITION WALLS be made to PREVENT the voices in adjoining rooms from being HEARD?_ A. The space between the laths (or canvass) should be filled with _shavings or saw-dust_; and then no sound would ever pass 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 pass 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_. Q. _Why can DEAF people hear through an EAR TRUMPET?_ A. The ear trumpet restrains _the spread of the voice_, and limits the _diameter of the sound-waves_; in consequence of which, their _strength_ is increased. Q. _Why are MOUNTAINS so NOISELESS and quiet?_ A. Because the air of mountains is _very rarefied_; and as the air becomes _rarefied_, sound becomes less _intense_. Q. _How do you know that the RARETY of air DIMINISHES the intensity of SOUND?_ A. If a bell be rung in the receiver of an air-pump, the sound becomes _fainter and fainter_ as the air is exhausted, till at last it is quite _inaudible_. Q. _What is the cause of ECHO?_