HYDRAULICS. 97 



To find the velocity of currents in drains, ditches. t 

 sluices, brooks, or rivers. 



RULE. Find the velocity of the surface of the current 

 in the middle of the stream by taking the number of inches 

 a floating body passes over it in one second. 



This, for all ordinary practical purposes, will be suffi- 

 cient. But to find the mean or average velocity, take the 

 square root of the velocity so found J double it, and deduct 

 it from the velocity at the top, and add one to the remainder, 

 and the result will be the velocity at the bottom. Add the 

 top and bottom velocities, and divide them by two for the 

 mean velocity. 



EXAMPLE. What is the mean velocity of a current, the 

 velocity of which at the surface, in the middle of the 

 stream, is 36 inches per second ? 



SOLUTION.- 4/86=6 x 2 = ] 236 = 24 + 1=25, velocity 



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