

REFLECTION OF SOUND. 343 



'fleeted sound is too feeble to be heard without special 

 mtrivances, and for the production of a distinctly 

 idible echo the wall of a large building is at least 

 squired. Beautiful echoes are produced by the straight 

 Dundaries of forests, the grandest of all by the steep 

 ,des of rocky mountains. Numerous feeble echoes are 

 mtinually produced in the streets of towns, but are 

 ,arcely ever noticed during day-time, being over- 

 owered by the general noise ; but in the night, when 

 ,ie streets are quiet, a short sound produced by 

 lamping the foot against the pavement or by clap- 

 ,ng the hands, is followed not only by one but 

 :equently by several echoes. If the street is nar- 

 :>w, the sound should be produced at one side, not 

 ; the middle of the street, so that it may have to 

 avel the whole available distance to the reflecting 

 urface. If we suppose the reflecting wall to be 17 m 

 l.bout 23 paces) distant from the point where the 

 fund is produced, the time required for the sound to 

 lach the wall is -3^ = -^th of a second ; an equal 

 Ingth of time is required for the reflected sound, or 

 U second will elapse between the production of the 

 sund and the perception of the reflection. This 

 ijterval is so short, that the primary and reflected 

 sund can only be distinguished if the original sound 

 >jis very sharp and quick, and sufficiently strong ; if 

 fese conditions are not fulfilled, as for instance in 

 cjiling out a person's name, the direct and the reflected 

 sand are confounded. When the distance of the re- 

 fjcting surface is greater, the reflected sound will 

 rourn after a longer interval of time, and according 

 t the length of this interval whole words, in some cases 



