218 



TEANSPORTATION OP DEBEIS BY RUNNING WATER. 



is given by Overstrain's data, above cited. 

 Such an inference is qualified as to Blue's data 

 by the possibility that the exponent is affected 

 in material degree by the form of the cross 

 section of the trough. 



Blue's data on velocity are of such character 

 as to warrant a fuller discussion than he gives. 

 His comparison with duty (q) is made without 

 regard to the accessory conditions of discharge, 

 depth, and slope, but we have seen that in 

 stream traction these conditions materially af- 

 fect the control of capacity and duty by mean 

 velocity. It is not practicable so to arrange 

 his data as to obtain results for the condition 

 that discharge, depth, or slope is constant, but 

 moderate approximations to such conditions 

 may be obtained by grouping. I have divided 

 his observations on the traction of beach sand 

 into three groups first, with reference to dis- 

 charge (+load); second, with reference to 

 depth; and, third, with reference to slope 

 and for each group have computed n on the 

 assumption that capacity varies with the nth 

 power of mean velocity. The resulting values 

 are given in Table 79, and with them are placed 

 the average of the corresponding exponents for 

 stream traction, derived under the several con- 



ditions of constant discharge, constant depth, 

 and constant slope (Table 53). 



It appears (1) that in flume traction capacity 

 is much more sensitive to variation of mean ve- 

 locity than in stream traction; and (2) that in 

 flume traction, as in stream traction, the order 

 of sensitiveness as related to conditions is 

 highest for constant discharge, intermediate for 

 constant depth, and lowest for constant slope. 

 In flume traction the sensitiveness appears to 

 vary directly with discharge and depth and 

 inversely with slope, while in stream traction 

 it was found to vary inversely with discharge 

 and slope, the variation with depth being in- 

 determinate. 



TABLE 7Q.^Value of n in C<x V m n , based on Blue's 

 experiments on flume traction of beach sand. 



