252 BELL SYSTEM TECHNICAL JOURNAL 



enhanced the necessary color effects. The relation between sound beam 

 width (in the optical direction) and light transmission was studied. In 

 general, the values of velocity obtained were found to be independent of 

 frequency, and the absorption to be proportional to frequency squared and 

 unrelated to calculated viscous and thermxal losses. A simple calculation 

 is proposed for estimating absorption errors caused by sound beam diffrac- 

 tion and spreading. These apply as well to absorption m.easured in other 

 methods than here used. 



