30 



situations, the observer can follow a particular wave crest only a 

 finite distance before it disappears. Close observation reveals that 

 the wave group mairitaLns its identity but that individual waves pass 



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through the group, rising up out of comparatively calm water at the 

 rear, reaching a maximum at the center, and then disappearing at 

 the front of the group. The phenomenon is similar to interference 

 in optics or beat frequency in acoustics. 



A small number of waves generated by a wave plunger in a straight 

 tank presents a most interesting phenomenon. If attention is fixed on 



