SOUND 



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with the sound waves on the outside to transmit a sensation to 

 the auditory nerve, and thence to the brain. 



If the number of vibrations of the sound waves is less than 

 16 per second, these little filaments are not affected and no sound 

 is heard. If the sound vibrations are more than 40,000 per second, 

 the auditory nerve is unaffected. 



It is believed by some that many insects produce sound waves with too 

 high a number of vibrations or too low a number of vibrations to be transmitted 

 into sound and heard by human beings. 



FIG. 3076. Here we see a sound-wave striking the drum of the ear. The 

 vibration moves the handle of the hammer which pulls the anvil and 

 pushes the stirrup, as shown by dotted lines, against the drum of the inner 

 ear. Tiny waves of the fluid inside this inner ear pass through a mem- 

 brane which lines the shell, and, traveling round the coils in the direc- 

 tion of the arrows, communicate the sensation to the nerve, and then 

 return by another canal. Courtesy of CMld Book of Knowledge , 



Echo. When sound waves are stopped by any object and sent 

 back again without being altered in shape, an echo is produced. 

 If the sound waves are broken and come back very irregular they 

 do not produce an echo. 



; The ancients believed that the echo was produced by a nymph, 

 Echo, a daughter of Air and Earth, The story goes that Echo -at 



