158 HYDRAULICS AND ITS APPLICATIONS 



As a very" close approximation we have 



if 

 1 o 



h) 



The value of C varies with the ratio ^ -r, and can only be deduced 



HI + h 



by experiment. 



The following mean values are obtained from the results of experiments 

 by Francis, and by Messrs. Fteley and Stearns : 



Francis. Depth of water at sill '85 to 2'3 feet. 1 



Messrs. Fteley and Stearns* 



Redtenbacher makes Ci = '57 and (? 2 = "62 in the above formula, 

 while Pestalozzi also makes C% equal to '62 and makes C\ vary from *534 

 to *566, diminishing as the ratio of J/ 2 to HI increases. It is indeed to 

 be expected that C* will be greater than Ci, since owing to eddy forma- 

 tion behind the weir the pressure on the discharge side of the crest will 

 be less than that corresponding to the assumed statical head HI Hz, 

 thus giving rise to an increased discharge over the lower portion of the 

 stream. 



The difficulty of obtaining accurate values of HI and H^, combined with 



1 Suppressed weir 22'2 feet long. " Trans. Am. Soc. C.E.,' : vol. 12. 



2 Suppressed weir 5 feet long. Values of HI from -3 to -8 foot. Crest 3'2 feet from 

 bottom of channel. " Trans. Am. Soc. C.E.," vol. 12. 



The results of experiments on submerged weirs 1 foot and 2 feet long, with two end 

 contractions, are given in Engineering News, New York, August 18, 1910, p. 174. 



