THE HOMEMADE ORCHESTRA 



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The rate of propagation varies according as the substance 

 through which the sound is traveling is more or less elastic. 

 Sound travels through water about four times as fast as through 

 air. It travels farther, also, the more elastic the conductor 

 is. One can hear an approaching train or wagon when the 

 ear is held on the rail or on the ground long before the rattle of 

 its approach can be heard through the air. The taut string or 

 the wire of the simple tin-can telephone (directions for making 

 given on p. 95 of the Field and Laboratory Guide in Physical 

 Nature-Study) carries the sound of the voice much farther 

 than it could be heard through the air. 



FIG. 1 66. Sound waves radiating from a bell 



Since sound travels in straight lines, there are sound shadows 

 just as there are light shadows; or, in other words, an object 

 shuts off the sound as it does the light. A block away from a 

 noisy thoroughfare, with its clanging street cars, automobile 

 horns, and rattling vehicles, one hears little of the hubbub, 

 for the intervening buildings shut off the sound waves. It 

 is true, however, that sound waves swing around the edges of an 

 obstruction much more readily than light does, for light waves are 

 very much smaller than are sound waves. The larger waves of deep 

 tones can do this more readily than do the smaller waves of shrill 

 sounds. Therefore the roar of the distant street is a hoarse roar. 



Sound, too, like light, is reflected from a surface. One may 

 focus sound with a concave mirror quite as readily as light. 

 (See Field and Laboratory Guide in Physical Nature-Study, 



