73 



0.17 



146 

 0.34 



312 

 0.72 



Figure 18. Response o£ a bed form to an increase in a (the mid- third 

 of test section in experiment 49) . Here N = 52, following 

 experiment 48 where N = 26. Upper and lower numbers by 

 each photo give n and (D/a)n, where n is the number of 

 cycles since the beginning of the experiment. 



