It will be noticed that the respective photographs and 

 the figures constructed by 



sin r V2 ^^'^^ 



where i and r are the angles of incidence and refraction, respect- 

 ively, and V, and V2 are the wave velocities in the two media, do 

 not agree. This is due to the fact that it was not possible to 

 get the water over the disc shallow enough for proper results. 

 When the water was made shallow enough, the waves would dissi- 

 pate as they passed over the disc. However, the picture taken 

 (fig. 7) does show refraction by a submerged circular shoal. 



Figure 8 shows the appropriate ray-wave crest diagram for 

 the two relative wave speeds involved, and it compares quite well 

 with the actual photograph (fig. 7). If the depth were shallower, 

 the rays would come to a focus inside the circle (Pierson, 1950). 

 8. Atmospheric refraction of sound waves caused by a uniform 

 temperature variation 



A practical application of refraction in the atmosphere is 

 the deviation of sound waves from a straight path due to the variation 

 of temperature with height. 



The velocity of sound in gases is given by the expression 



v=/^ (8.1) 



where p is the pressure of the gas, p is the density of the medium, 

 and Y is the ratio of the specific heat of the gas at constant 

 pressure to the specific heat at constant volume (y = 1.4-0 for air). 



22 



