i6o The Drainage of Fens and Low Lands, 



I cubic metre of water = <^*9^S ^^'^' 



I hectolitre of coal . . = about 2| bushels, and weighs 



about 1 4 cwt. 

 I kilogramme per square 



centimetre . . . . = 14." 22128, &c. lb. per squaie inch. 



TABLE III. 



For ascertaining the pressure and velocity of water. 



The pressure in lbs. per 



square foot . . . . = height in feet multiplied by 



62*5 lb. 

 The pressure in lbs. per 



square inch . . . . = height in feet multiplied by 



0-4335 lb. 

 Height in feet . . . . = pressure per square inch 



multiplied by 2 • 307. 



The velocity of water theoretically is found by the formula 

 Y=^^2g/i, where V == velocity in feet per second; ^, the 

 velocity of a body falling freely for one second, or 32*182 feet. 

 /i = the height or vertical distance in feet through which the body 

 passes. This is generally taken for practical purposes as eight times 

 the square root of the head. 



The theoretical velocity has to be reduced for loss by friction, &c., 

 varying according to the character of the opening of channel through 

 which the water passes. The result, as found above, therefore, has 

 to be multiplied by one of the following constants which have been 

 determined by experiment : — 



Formulae V = 8 V/2 X ^, and 



^^= (^y* 



Bxc 



h = height in feet. In the case of sluices or bridges, this is the 

 vertical difference in the surface of the water above and 

 below the opening. 

 V = velocity in feet per second. 

 c = constant. 

 = opening of a bridge or sluice with pointed piers and smooth 

 masonry . . •96 



