ECHO. 417 



A. 1st Because the sound-waves 

 cannot pass beyond the cavern or grotto, 

 and must flow back : 



2ndly The return waves (being en- 

 tangled by the cavern) are detained for a 

 short time, and come deliberately to the 

 ear. 



Q. Why are antique halls, winding passages, 

 and cathedral aisles FAMOUS for ECHOES? 



A. Because the sound-waves cannot 

 flow freely forward, but strike against 

 the winding walls perpetually, and are 

 beaten back. 



Q. Why are MOUNTAINS and ice-bergs FAMOUS 

 for ECHOES ? 



A. Because they present a barrier to 

 the sound-waves which they cannot pass ; 

 and are sufficiently elastic to throw them 

 back. 



Q. WJiy do not the WALLS of a ROOM or 

 church produce ECHO ? 



A. Because sound travels with such 

 velocity, that the echo is blended with the 

 original sound, and produce but one 

 impression on the ear. 



Sound travels 13 miles in a minute. 



