158 



SEWER DESIGN 



now it is used only as an index of the transporting power. 

 As Mr. Hooker intimates, the whole subject is far from being 

 on a satisfactory basis, and observation and experiments are 

 much needed to put the matter in its true light. 



The available experiments on the velocity required to take 

 up into suspension or to drag along material in running water 

 are not many. Table XX, taken from Mr. Hooker's article, 

 gives what there are. 



It is seen that a velocity varying from 16 to 60 inches per 

 second is required to take up material, and Baldwin Latham 

 gives the following table showing how the specific gravity of 

 the material affects that velocity. The experiments on which 

 this is based were made by Mr. T. E. Blackwell, C.E., for the 

 government referees, in the plan of the Main Drainage of the 

 City of London. 



TABLE XXI 



Evidently other conditions than the specific gravity are 

 concerned, and as no dimensions are given, it is probable that 

 there was a variation in the size of the pieces tested and, what 

 is probably of more active importance, in the shape of the 

 pieces. In a thesis on Flushing- waves, in 1894, Messrs. Fort 



