2/0 SOUND 



at A is transmitted to B without any perceptible motion of 

 the balls lying between these points. Similarly the particles 



o oooo- 



I / 



FlG. 169. Elastic balls transmit motion. 



of air set into motion by a sounding body impart their motion 

 to each other, the motion being transmitted onward without 

 any perceptible motion of the air itself. When this motion 

 reaches the ear, it sets the drum of the ear into vibration, and 

 these vibrations are in turn transmitted to the auditory nerves, 

 which interpret the motion as sound. 



253. Why Sound dies away with Distance. Since the last ball 

 B is driven outward with a force nearly equal to that possessed 

 by A, it would seem that the effect on the ear drum should 

 be independent of distance and that a sound should be heard 

 as distinctly when remote as when near. But we know from 



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\ 



71 ' 



FlG. 170. When a ball meets more than one ball, it divides its motion. 



experience that this is not true, because the more distant the 

 source of sound, the fainter the impression ; and finally, if 



