266 Ground Water, Wells and Farm Drainage. 



Table showing observed and computed flow of water through 

 simple sands of different diameters under a pressure of 

 I c. m. of water. 



The agreement between the observed and computed flows 

 is not as close as could be wished but when it is observed 

 that the flow of air, from which the diameters were com- 

 puted, was not measured through the same sample as the 

 one through which the flow of water was measured, that 

 the pieces of apparatus were not the same and that the flow 

 varies, theoretically, as the squares of the diameters of the 

 soil grains, it must be conceded that there is much more 

 dian a chance agreement. 



The samples of sand used in these trials are represented 

 full size in Fig. 98. 



331. Relation of Observed Flow to Diameter of Soil 

 Grains. If the squares of the diameters of the sand grains 

 represented in Fig. 96 are plotted as abscissas and the ob- 

 served and computed flows as ordinates their relations will 

 be as shown in Fig. 95, where it is clear that the rates are 

 such as to agree reasonably well with the squares of the 

 diameters of the grains. 



332. Relation of Pressure to Flow Through Sands. Most 

 experimenters along this line have found that while there 

 is a general tendency for the flow to increase directly as the 

 pressure there are nevertheless conditions which prevent 



