THE IRRIGATION AGE. 149 



away from each other so that one will not rob the other, and then be 

 connected to suction pipe below pump cylinder. 



Screen points should never be less than two-thirds (if) the diame- 

 ter of the cylinder. Screen points as large in diameter as the cylinder 

 give still better results. The length of screen points to use will de- 

 pend on the thickness of the water bearing sand strata. As a rule 

 the coarsest sand and gravel is found at the very bottom of the water 

 bearing strata, therefore the screen point should be put down to bot- 

 tom of the water bearing strata. 



Everything else being equal, screen points of large diameter will 

 supply water faster than smaller ones, and when lodged at bottom of 

 water bearing strata, in the coarser sand and gravel, will supply much 

 more water than when lodged higher up in the strata, where there is 

 less gravel and the sand is fine. In river bottoms, where the water 

 bearing sand stratas are sometimes found to toe 100 feet or more in 

 thickness, it will not be necessary to put the screen point down to the 

 bottom of the strata, but close attention must be given to coarseness 

 of the sand or gravel in which the screen point is lodged. 



Under no circumstances should the point be lodged in anything 

 but the coarsest sand or gravel. Screen points not less than ten feet 

 long should be used where there is enough coarse sand or gravel in 

 the water bearing sand to permit doing so. 



In every instance where a 10 foot screen point is used, and there 

 is enough water bearing sand to permit it, the top screen point should 

 be at least fifteen feet below water level. In water bearing sand 

 stratas which are two shallow, that is, too thin to admit of points ten 

 feet long being used, shorter ones should be used. In wells where the 

 water bearing sand stratas are only a few feet thick, sand points must 

 be only of such length as will insure the top of the screen to be en- 

 tirely under water, so as to prevent air from finding its way into the 

 pipe below cylinder. Large screen points are sold by the foot and 

 can be bought in any length from two to ten feet long. It must be 

 obvious that no more water can be pumped than the well affords. 

 Therefore the necessity of limiting the size of the pump to the capacity 

 of the well. 



Open well making, where open wells can be successfully used, is 

 so generally understood that only wells where screen points are to 

 be used will be considered in this connection. 



To put down screen points, make an open well large enough to 

 afford room for two men to work in and sink it down to water bearing 

 sand and curb it to prevent caving in. After this is done, it is more 

 satisfactory to bore down through the water bearing strata so as to 

 learn its thickness. A piece of gas pipe, of sufficient inside diameter 

 to admit the use of a common auger, may be used for casing, and if 



