EXAMPLE. 231 



should use 9 5 , where a n denotes the area of the low- 



n 2 

 est transverse section, and instead of 



f I P 



J a + 



the sum of all the similar values for the different portions 

 of the stream should be used. (See Weisbach's Mechs., 

 p. 969 ; also Tate's Mech. Phil., p. 305.) 



EXAMPLE. 



A stream falls 9.6 inches in 300 feet, the mean value of 

 its wetted perimeter is 40 feet, the area of its upper trans- 

 verse section is 70 square feet, and that of its lower is 60 

 square feet. Find the discharge of this stream. 



From (11), we have 



8.025\/OT8 

 v = 



60 2 



7.178 



J- 4. 0007565^-^^ l \ 



" 702 + 130 Uo 2 + m 



= 354 cubic feet. 



A/0.0000731 + 0.0003365 

 The mean velocity is 



2Q 709 



2 = - - = 5.45 feet : 

 + ! 130 



hence (Art. 122), a more accurate value of /is 0.00768, and 

 therefore we have 



= 352 5 



VO. 0000731 + 0.0003416 



If the same stream has at another place a fall of 11 inches 

 in 450 feet, and if the area of its upper transverse section is 



