98 HYDRAULICS. 



at bottom; then, 36 + 25 61-^2=30.5 inches per second, 

 mean velocity. Ans. 



To fond the volume of water discharged by drains, sluices, 

 brooks, <&c., of given dimensions, in a given time. 



RULE. Multiply the velocity of the current per second 

 in feet, by the area of the transverse section of the drain 

 or sluice, in feet, and the product will be the quantity dis- 

 charged per second, in cubic feet. 



EXAMPLE. What volume of water will a drain 2 feet 

 wide and 3 feet deep discharge in one hour, the mean velo- 

 city of the current being 30 inches per second ? 



SOLUTION. 2x3=6 sq. ft., area of section x 2 J- ft., velo- 

 city, =15 cubic feet discharged per second; then, 15 x 

 3600 seconds (one hour) =54,000 cubic feet per hour. 

 Ans. 



NOTE. The standard gallon contains 231 cubic inches, 

 and a cubic foot contains 1728 cubic inches. Accordingly, 

 a cubic foot of water contains 7.476 standard gallons. 

 Hence, if we multiply the number of cubic feet *by 7.476, 

 it will give the number of gallons. For instance, the drain 

 in the above example discharges 54,000 cubic feet per 

 hour, which, multiplied by 7.476, gives 403,704 gallons 

 discharged per hour. 



To find the velocity of water running through pipes. 

 RULE. Multiply the height of the head in feet by 2500 ; 

 divide this product by a divisor obtained as follows : Di- 



