between $ and Y . On the same figure a family of theoretical curves was 

 drawn as it has been explained in section 5 of the text. These curves 

 are the graphical representation of equation (4-27) in which the values 

 A* and B* were equal to unity. Each curve corresponds to a particular 



value of ■=;- . One may observe that the theoretical curve with — = 1.5 



M o T| 



is very similar to the experimental one but offset both in the vertical 

 and the horizontal. A parallel translation of the latter by a factor 30 

 along the horizontal and by a factor 4 along the vertical makes it prac- 

 tically to coincide with the former. This means that the values of $ 



and Y, satisfying equation (4-27) with A* - 30, B* - 4 and _- = 1.5 



Ho 

 under any set of experimental conditions will be very close to the values 

 of the same parameters calculated directly from measured quantities. In 

 conclusion we set forth the claim that a theoretical curve constructed 

 from equation (4-27) with the constants as determined here could be used 

 to describe the relationship between the two functions $ and Y. 



Several reviewers in the past and more recently P. Lhermitte (1961) 

 are rather critical of Li's and Manohar's experiments. More specifically 

 they express some reservations about the applicability of the results in 

 an actual case on the ground that in the experimental flume an inertia 

 force is induced on the particle which in the prototype is absent. Their 

 contention is that this force is significant and consequently cannot be 

 ignored. Since the same flume was used in the present study one may 

 anticipate similar criticism especially in connection with the determina- 

 tion of qg from direct measurement. 



We believe, however, that the criticism is not fully justified be- 

 cause this inertia force under the average experimental conditions is 

 indeed small compared to other forces acting simultaneously on the 

 particle. The maximum value of the angular velocity in the set of runs 

 with a = 1.25 feet was uj = 1.86 rad/sec. corresponding to a maximum tan- 

 gential acceleration of 



au> 2 = 1.25 x 1.86 2 = 4.32 ft/sec 2 



which is much smaller than g. The tangential force could have some 

 effect in setting the particle into motion if it were in phase with the 

 lift in which case the combined effect could not be ignored. Since the 

 two forces are 90 degrees out of phase the instant one reaches its maxi- 

 mum value the other is practically equal to zero. Therefore it is 

 justifiable to base the condition of equilibrium on the balance of the 

 vertical forces whose absolute value is relatively large and ignore the 

 effect of a much smaller horizontal component which is fully out of 

 phase. 



C-3 



