HYDRAULICS. 205 



and for rivers or open canals, 



V = . 1541131 + \J 023751 -f 32806 . 6 X HI . 



These formulas give the velocity in English feet ; those 

 of PROXY give it in metres ; see the work just quot- 

 ed, 209, 210.; also Note prefixed to Table ii. 

 p. 110. It must be observed, that when the water 

 from the lower end of the pipe is discharged into the 

 air, A'-O. 



From the comparison that has been made of these for- 

 mulas with actual experiments, they appear to be 

 very accurate. The numbers or constant quantities 

 may perhaps require some correction, but there is no 

 doubt that the form of the expression is exact. They 

 must therefore supersede the use of Du BUAT*S more 

 complicated theorems. 



296. When the sections of a river vary, the 

 quantity of water remaining the same, the mean 

 velocities are inversely as the areas of the sec- 

 tions. 



a. This must happen, in order to preserve the same 

 quantity of discharge. 



1). When the water in a river receives a permanent 

 addition, the velocity is immediately increased. The 

 increase of the velocity augments the action on the 

 sides and bottom, in consequence of which the width 

 is augmented, and sometimes also, but more rarely, 

 the depth. The velocity is thus diminished, till the 



tenacity 



