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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



Fig. 26 — Examples of refraction and focusing effects for sound waves. 



and these have shown relaxations in such plastics as polyethylene and 

 nylon 6-6. The simplest method for measuring one of the properties for 

 longitudinal waves, i.e., the attenuation, is to measure the change in 

 loss between two transducers in a liquid such as water, caused by insert- 

 ing a sheet of the material. This process, used during the last war, 

 results in the losses in db per centimeter for several rubbers and plastics, 

 shown by Fig. 24. Indications of relaxation mechanisms are given by 

 the rubbers and the plastic tenite II which is a cellulose acetate butyrate. 

 The first fairly accurate method for measuring longitudinal sound 



