280 Ground Water, Wells and Farm Drainage. 



pected, and Slichter computes that three wells 2 inches, 6 

 inches and 12 inches in diameter respectively, if sunk 100 

 feet into a bed of sandstone having sand grains .25 mm. in 

 diameter and a pore space of 32 per cent, will have capaci- 

 ties in cubic feet per minute as follows, when the water is 

 lowered 20 feet: 



Diameter. Diameter. Diameter. 



2 inch. b inch. 12 inch. 



Cubic ft. per minute.... 31.90 36.94 44.45 



These amounts are on the assumption that the walls of 

 the w r ell or casing offer no resistance to the discharge, 

 which of course is not true, and the 2-inch well could not 

 discharge the amount indicated under the pressure of 20 

 feet although that amount could enter the well if it were 

 removed fast enough. 



FIG. f08. Shows a good form of sand strainer made by sawing slots in 



brass tubing. 



It is clear from these results that for most wells there is 

 little gained in making them larger in diameter than is 

 needed to provide accommodation for the pump. 



