DUTY AND MEASUREMENT OF WATER. 1 65 



sixty. Divide the gallons per hour by 38 to obtain the 

 acre inches per month, or by 13 for the acre inches in 

 three months. These results are not mathematically 

 accurate, but will be found close enough for ordinary 

 computations. They make no allowance for seepage 

 and evaporation. 



A safe rule for finding the capacity of a cylindrical 

 cistern is to take the dimensions in inches, square the 

 diameter, multiply by the depth, and then by .0034, 

 which will give the contents in United States standard 

 gallons. Thus to find the capacity of a cistern twenty- 

 five feet in diameter and one foot deep, multiply: 300 

 X 12 X .0034 = 3672 United States standard gallons. 



To measure flowing water in ditches, canals, and 

 rivers multiply the area by the mean velocity of its flow 

 in feet per second, and the producft is the volume in 

 cubic feet ; divide the number of cubic feet by 1.57, 

 and the result will be the number of the miner's inches. 



