WATER SUPPLY. 125 



over six or eight feet in diameter should have an eight- 

 inch wall to resist the outside pressure, especially if the 

 soil IS of grayel or sand. To lay 1,000 bricks two bar- 

 rels of cement will be required, if used clear ; but there 

 may be one, or two, or even three barrels of sand used to 

 one of cement, without danger of weakening the wall. 

 Where expense is no object as compared with durability, 

 we would use clear cement. Rosendale (American) ce- 

 ment is good enough for all purposes. 



To ascertain the contents of a cistern the diameter is 

 multiplied by itself, or squared, and this product is mul- 

 tiplied by . 7854. It will be near enough to take three- 

 quarters of the product in feet and multiply this by the 

 depth in feet. This gives the number of cubic feet of 

 water in the cistern, A cubic foot of water is equal to 

 seven and a half gallons. Thus in figuring for a cistern 

 the desired size may soon be ascertained. By doub- 

 ling tlie diameter, the contents are increased fourfold. 

 Thus a round cistern four feet in diameter will hold a 

 little over three barrels for every foot in depth; if eight 

 feet in diameter, it will hold twelve and one-half barrels 

 for every foot ; but if twelve feet in diameter, it will hold 

 nine times as much; for if the diameter is enlarged three 

 times, the contents are increased three times three, or 

 nine times, and if enlarged four times, or to sixteen feet, 

 the cistern will hold four times four, or sixteen times as 

 much water for every foot in depth. Thus a great ad- 

 vantage is gained by making the cistern as wide as pos- 

 sible. The following table will be found useful for 

 reference: 



Contents of a round cistern for every foot in depth of 



