CHAPTER XII 



THE RELATION OF SOUND AND MUSIC TO US 



SOUND 



Sound Waves. We have learned that light comes to us through 

 a series of waves which affect the optic nerve. Waves which are pro- 

 duced in the atmosphere we call sound waves. They affect the audi- 

 tory nerve of the ear. As sound is the result produced by the waves 

 striking the ear drum and sending a sensation over the auditory nerve 

 to the brain, sound is really in the head. The waves themselves do 

 not produce any sound. There are as many sounds in a place as 

 there are ears to receive the sound. If one should strike a blow and 

 extend his finger in front of him, there would be no sound at the end 

 of his finger. Sound waves, however, might beat against the finger 

 and also pass on until they reach some body which is capable of 

 receiving the sound waves on some tissue which will produce a sen- 

 sation of sound. 



Sound waves move out in a straight line from their source, not 

 like the waves of the ocean but in a backward and forward motion, 

 on the same principle as when one billiard ball strikes another, 

 forcing ahead the one that is hit. If the second ball hits a third, 

 the third is pushed forward, and so on. 



Sources of Sound Waves. Sound waves are produced from 

 vibrating bodies. Something must move in order to set the air in 

 motion. There are many sound waves which do not produce sounds 

 to the human ear. Some bodies vibrate so rapidly that they send 

 off a series of sound waves which hit the ear drum with a greater 

 rapidity than the auditory nerve can receive and form into sen- 

 sations of sound. A body vibrating sixteen times per second pro- 

 duces the lowest sound we are able to hear. 



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