

REFLECTION OF SOUND. 341 



wo threads to the arm of the retort stand is set into 

 visible motion by it. 



When a drop of water is allowed to fall upon the 

 niddle of the water contained in a circular basin or 

 : }late, the wave thus produced is seen gradually to en- 

 arge and to spread in the form of a ring until it reaches 

 lie side of the vessel; here the wave does not disappear 

 3ut it returns again, forming a ring which becomes 



FIG. 212. 



;radually narrower and contracts at the middle. We 

 jay in this case that the wave is reflected by the side of 

 he vessel. If the ' reflection ' takes place at a straight 

 , such as the side of a square trough, the reflected 

 does not return to the point from which it started 

 ;ut spreads out backwards, after reflection, in the same 

 lanner as if it had been produced at a point as far 

 Behind the wall as the point where it was really pro- 

 uced is iii front of the wall. Fig. 212 shows what is 

 sen as the result of producing successively several 



