HYDRAULICS. 201 



quantity, viz. the quotient obtained by dividing the 

 area of the transverse section of the stream, express- 

 ed in square inches, by the boundary or perimeter of 

 that section, minus the superficial breadth of the 

 stream, expressed in linear inches. 



The mean velocity is that with which, if all the parti- 

 cles were to move, the discharge would be the same 

 with the actual discharge. 



The line R is called by Du BUAT the radius 9 and by Dr 

 ROBISON the hydraulic mean depth. As its affinity 

 to the radius of a circle seems greater than to the 

 depth of a river, we shall call it, with the former, 

 the radius of the section. 



Lastly, Let S be the denominator of a fraction which 

 expresses the slope, the numerator being unity, that 

 is, let it be the quotient obtained by dividing the 

 length of the stream, supposing it extended in a 

 straight line, by the difference of level of its two 

 extremities ; or, which is nearly the same, let it be 

 the co-tangent of the inclination or slope. 



292. The above denominations being understood, 

 and the section, as well as the velocity being sup- 

 posed uniform, 



307 R* ~ 



A R J 1 



1 " ; 



S _ og (s + 1.6) 



or 



