338 SPEAKING -TUBES EAR-TRUMPETS. 



Sound transmitted by air will be propagated wit 

 nearly undiminished strength if the sonorous vibratio 

 are prevented from spreading in different directior 

 A tube of sheet metal, open at both ends and about 3 

 wide, may be used for showing this fact. The aerial vibr 

 tions produced by speaking into such a tube are pr 

 vented by its sides from spreading all round, and n 

 through the length of the tube losing only little of the 

 intensity by the friction of the air against the side 

 and by the vibrations which they communicate to t 

 tube itself. Such tubes, called ' speaking-tubes/ 

 in common use wherever sound has to be transmitt 

 over considerable distances or between separate roon 

 as on board ship, in hotels, manufactories, etc. T 

 transmission of sound through such tubes is not int( 

 fered with by their passing through walls, ceilings, et 

 nor is the intensity much diminished by angles a 

 bends in their course. Smaller flexible tubes are oft 

 used with advantage by deaf persons as c ear-trumpe 

 one end being inserted in the ear, while the pers 

 speaking holds the other end, which forms a funn 

 shaped enlargement, near the mouth. 



The effect of such a tube can easily be observed by inseri : 

 one end of an india-rubber tube a few meters long, and 6 or 

 wide, into the tube of the ear, so as to be in close contact with 

 auditory organ. If now a tuning-fork be gently struck by anoi 

 person, and held near the other end of the tube, the sound is h( 

 as distinctly as if the tuning-fork were close to the ear itself. 

 tuning-fork is not at hand, the slight sound produced by rubl 

 together the edges of two finger-nails may be substituted. 



The ' speaking-trumpet ' is much less effective tl 

 speaking-tubes and ear-trumpets. It is conical, mi 

 wider at one end, and provided with a mouthpiece 



