268 Ground Water, Wells, and Farm Drainage. 



50 c. m. long the flow increased faster than the pressure; 

 but when the column was 75 c. in. long the flow increased 

 directly as the pressure, while when it was made 100 c. m. 

 long then the flow did not increase as rapidly as the pres- 

 sure. 



-I20O 



Fio. 98. Showing the observed relation of pressure to flow of watei 

 through sandstone, as measured in the apparatus of Fig. 99. 



333. Relation of Pressure to Flow Through Sandstone. 

 When the flow of water is measured through sandstones 

 such as constitute most water-bearing beds it is often found 

 that here, as in the sands, the flow may increase in a much 

 higher ratio than the pressure. Three series of such obser- 

 vations are plotted in Fig. 98, and the apparatus used is 

 shown in Fig. 99. 



Where the flow does not increase as rapidly as the pres- 

 sure the departure from the theoretical flow has been ex- 

 plained by assuming that the currents become turbulent 

 and thus reduce the discharge; but no satisfactory reason 

 has yet been assigned to the cases where the flow increases 

 faster than the pressure. 



334. Observed Rates of Flow of Water Through Sands and 

 Sandstones. The observed rates of flow of water through 

 the series of sands represented in Fig. 96, when expressed 



