In order to gain a better understanding of the soft wall 

 cavity an attempt has been made in section IV to develop a 

 foundation for the theory describing some of the basic 

 characteristics of the system. An approach to this prob- 

 lem had been made by Toulis. S6 The theory developed in 

 section IV follows the procedure for room acoustic theory 

 discussed by Hunt, 27,2S , Morse, 29 and Morse and Bolt. 30 

 However, it was necessary to employ the wave equation 

 for a viscous medium. In this connection the phenomeno- 

 logical approach suggested by Markham, et. _al.''" and 

 Skudrzyk' 1 "'' served as a guide. 



The wave equation utilized in section IV considers the 

 first and second coefficients of viscosity as independent. 

 The question of the relationship between the first and 

 second coefficient of viscosity has been much debated 

 since Stokes' original paper on this problem 31 and it can- 

 not be claimed to be fully resolved. 12 ' 32 This question, 

 although pertinent to the quantitative evaluation of the 

 theory, does not have any particular bearing on the qual- 

 itative nature of the results. 



INFLUENCE OF AIR BUBBLES 



The presence of air in water has a significant effect 



only when in the form of bubbles. Dissolved air changes 



the sound velocity by less than 10 parts per million 33 and 



the attenuation coefficient at ultra-high frequencies is 



virtually unchanged within the tolerance of measurement 

 „„„„„ 20 



The anomalous attenuation and change in propagation 

 speed for frothy liquids was noted in 1911 by Mallock. 34 

 A recent survey of the subject is given by Devin. 3E He 

 considers the damping caused by a single bubble in water. 



""Ref. 15, p. 37 3 



**Ref. 4, p. 762-766, 775-783 



