WATER SUPPLY FOR THE FARM. 533 



be turned off for a few moments after it commences raining, to prevent the dirty water enter 

 ing it, after which, the roofs becoming sufficiently washed, the pipes can be re-adjusted to 

 supply the cistern. 



Table of Contents for Circular Cisterns. The following table of contents may 

 be of assistance to those designing to build cisterns. For each foot in dspth, the contents of 

 circular cisterns is as follows: 



A cistern 5 feet in diameter will hold for every foot in depth, . . . 4.66 barrels. 



6 &quot; &quot; ... 6.71 



7 &quot; ... 9.13 &quot; 



8 &quot; &quot; ... 11.93 &quot; 



&quot;9 &quot; &quot; ... 15.10 



&amp;lt; 10 &quot; ... 18.65 &quot; 



A cistern 3 feet diameter will hold for every 10 inches hi depth, . . 59 gallons. 



4 &quot; . 78 



4^ &quot; &quot; . 99 &quot; 



5 &quot; . 122 

 5i &quot; &quot; . 148 



6 &quot; . 176 

 8 &quot; 310 



By the above table, it will be seen that a cistern five feet in diameter and six feet deep 

 will hold nearly twenty-eight barrels; eight feet in diameter, and ten feet deep, 119.3 barrels, 

 and so on. 



Rule for finding the contents of any circular cistern in wine gallons, the diameter and 

 depth being known 



1. Find the square of one-half of the diameter, and multiply the product by 3^, which 

 will give the area of the bottom of the cistern nearly. 



2. Multiply the product thus obtained by the number of feet in depth, which will give 

 the cubic contents in feet. 



3. Multiply this last product by 1,728 (the number of cubic inches in a foot) which will 

 give the number of cubic inches. 



4. Divide the result thus obtained by 231 (the number of cubic inches in a wine gallon), 

 which will give the number of gallons in a cistern. 



By dividing the number of gallons in capacity by the number of gallons in a barrel, we 

 have the capacity of the cistern given in barrels. 



Filters for Cisterns. In making cisterns, it is very essential that arrangements be 

 furnished for filtering the water as it is received from the pipes of the roof. By the filter 

 ing process, all the suspended impurities, such as mud, animal and vegetable substances, etc., 

 are removed from the water. 



The usual method is to divide the cistern into two equal compartments by a wall of brick, 

 which is open at the bottom to the height of six or eight inches. One of these compartments 

 is for receiving the water from the roof, and the other for containing it when it is filtered, 

 ready for use. 



In the bottom of the one for receiving the water, alternate layers of pounded charcoal, 

 sand, and gravel are placed to a little more than the depth of the bottom opening between 

 the partitions. In the filtered department it is filled to the same height as the former, with 

 clean sand and gravel. Since the water passes through all these layers in reaching the 

 filtered department, it will be comparatively pure by this process. Of course, the pipe from 

 the roof enters the former compartment, and that of the pump the latter. In making such a 

 cistern, it would be well to build the wall forming the partition between the two compart 

 ments with a curve, so as to act as an arch towards the unfiltered portion,or side that is always 

 fullest, setting the ends firmly into the sides of the cistern. This form will counteract the 



