342 REFLECTION OF SOUND. 



waves at a ; the reflected waves spread as if they wer< 

 produced at b. 



Waves transmitted by solid bodies are also capable o 



being reflected if they reach the surface of another body 



If a piece of cord, 5 m or 10 m long, is tied at one end t< 



a fixed point (a hook or a door-handle), and the othe 



end is held by the hand, the cord being moderatel 1 



stretched so as just to be horizontal, and that end i 



slightly jerked either downwards or to the side, an un 



dulation will be transmitted along the cord which i 



seen to return after having reached the opposite fixe 



point. If both ends of the cord are fixed and the latte 



plucked somewhat aside by two fingers placed near on 



end, the wave is seen to travel backwards and fbrwarci 



several times, being repeatedly reflected at each enr 



If, in the experiments on the propagation of sound, a 



iron wire a few hundred metres long be used, and 



single vigorous knock be given to the sounding-be 



with a small stick, the sound will be heard at each er! 



six or eight times, its intensity gradually diminishin;: 



the wave which travels along the wire is repeatedly r 



fleeted at each end. The reflection cannot be perceivd 



distinctly with short wires, because the velocity ! 



propagation in iron is extremely great, and hence t 



wave returns so rapidly to the starting-point tl) 



the ear is unable to distinguish the rapidly succeedin 



sounds. 



When sound-waves, which are propagated throm 

 the air, meet with any obstacle, as for instance a lair 

 solid surface, the waves are reflected. This refl'j- 

 tion produces the echo. Solid bodies with a smjl 

 extent of surface also reflect sound-waves, but 1? 



