in units that can be easily interpreted, instead of db/sec. 

 Some Final Remarks Regarding the Theory 



The most general boundary conditions considered 

 required the determination of p and v n at the boundary. 

 The pressure p was determined from equation la, with 

 the simplification that \a and \ l were zero. These terms, 

 however, can still be disregarded as long as the viscous 

 part of the pressure tensor is insignificant compared with 

 the elastic part. This same approximation has been used 

 in the preceding analyses. 



In the more general case, the velocity at the boundary 

 must now satisfy one further condition, beyond the condi- 

 tion imposed by the acoustical impedance of the boundary. 

 This condition is that the component of the velocity tangential 

 to the boundary must vanish. To satisfy this boundary condi- 

 tion, there must exist a transverse frictional wave in the 

 immediate neighborhood of the boundary, since such waves 

 experience an extremely high attenuation with distance. 

 This will add to the boundary losses, but these are deter- 

 mined experimentally in any event. It must be borne in 

 mind, however, that the reference liquid should have approx- 

 imately the same shear coefficient \jl as the liquid under 

 investigation, and approximately the same sound velocity c. 



59 



