The period T, when not independently chosen, is denoted T^ or Tj., 

 for conditions of initiation of grain motion or of spontaneous ripple 

 formation. The maximum horizontal velocity is simply 



^ C16) 



and <j) is given by equation (1) . The tables in Appendix A include 

 observed values of ripple length and height which are discussed in 

 Sections IV, 4 and V,3. The chronological sequence of the experiments 

 in the tables is emphasized because the final bed form of one experiment 

 was often the initial bed form of the next, and because in a known 

 sequence of combinations of a and T the return to an earlier combina- 

 tion permits observation of any hysteresis. The duration of each experi- 

 ment is given to help assess the steadiness of final conditions. 

 Experiments with smaller (^ and less intense sand motion tend naturally 

 to be longer. In a few cases steady conditions were probably not 

 attained. 



Appendix A shows that the ranges of a, T, and U were: 



9.15 centimeters < a < 45.8 centimeters 



1.60 seconds < T < 16.0 seconds 



18.0 centimeters per second < U < 77.1 centimeters per second 



The upper limit on U was found necessary to forestall damage to the 

 screens by the flow forces which increased rapidly as the screens became 

 clogged by sand carried in suspension. 



Table 1 contains symbols for the experiments which show their values 

 of D and N, and, hence, a/D. Increasing a/D is shown by a clockwise 

 progression of a flag on each symbol. 



In Figures 9, 10, and 11 (one for each sand) N has been plotted 

 against T with the number of each experiment. An asterisk denotes an 

 experiment with the bed initially leveled. These plots serve to clarify 

 the range and sequence of the experiments. On these logarithmic plots, 

 lines of constant U have a slope of plus one, and two such lines, for 

 values of U encompassing all the points, are drawn on each plot. 

 Curves show the observed Tj, as function of a. It should be remembered 

 that, except when T is Tc or T^., Figures 9, 10, and 11 merely display a 

 pattern of independent variables. 



33 



