FLOW OF WATER IN CHANNELS AND PIPES. 53 



truly accurate and satisfactory manner, it remains to 

 calculate the flow by means of a satisfactory formula. 

 We want to find the depth of water flowing over it 

 = H and the breadth of the weir L. 



There are various formulae in general use. Those 

 which are simplest, provided they give accurate 

 results, are necessarily the most satisfactory. 



Q = quantity in cub. ft. per second. 



Then first we have Mr. James B. Francis' equation, 



or if we can only measure the depth on the sill in 

 inches conveniently = //, 



These equations assume a double end contraction. 

 If there is none Q = 3-33 LH VH . . . (4) 

 Q='o8oi Lhjh . . . (5) 

 Again, there is Mr. Thomas Hawkesly's formula, 



Q* = *L^ . . (6) 



In this case Q^ = gallons per second. 



But we have only been dealing with rectangular 

 notches. It is often convenient _ t . . , 



iw/ >' Wjf ~}~ I *J*J*t ' 



not to make them that shape, 

 but to make them in the form 



of the Cippoletti weir, as fig. 44. 



The formula to use is FlG - 44 ' 



Q - 3-367 LH>/H . . (7) 



Q=-o8iL/i x /S . . . (8) 



For very small flows the V notch is a very useful, 



