90 



MB. W. B. BALDWIN- WISEMAN ON 



[Feb. 1907. 



and the critical pressure was manifested at the low pressures of 

 5 and 10 lbs. per square inch for the Mottisfont and Micheldever 

 Chalk. In the coarser interstices of the Millstone Grit the flow was 

 comparatively slow, and the critical pressure was not attained until 

 the relatively-high pressures of 60 and 35 lbs. per square inch were 

 reached, for the 6-inch and 3-inch thicknesses of stone respectively ; 

 while, in the coarse interstices of the Daresbury Sandstone, the flow 

 was very rapid compared with that in the other rocks under similar 

 pressures, and the critical pressure was in evidence at the com- 

 paratively low pressures of 20 and 15 lbs. per square inch for 

 the 6-inch and 3-inch thicknesses respectively. With these ex- 

 periments in mind, it is therefore not surprising that different 

 investigators have formulated somewhat conflicting statements — 

 based upon experimental data, derived generally from pumping 

 experiments which they have conducted — to the effect that the 

 flow varied directly with, or faster than, or more slowly than, the 

 pressure : the deductions being entirely dependent on the relation of 

 the range of pressure considered, to the critical pressure for flow in 

 that particular rock. 



It is, of course, highly probable that differences of pressure as 

 great as those in my series of experiments are far in excess of the 

 differences pertaining to normal natural sub-surface flow, but they 

 serve to afford data in pumping investigations, as I have proved 

 in the paper (24) to which I have previously referred. Thus, in a 

 well, the inflow at the apex of the cone of depletion is accelerated 

 by the removal of the column of water between the rest-level and 

 the reduced working-level of the water when pumping, the pressure 

 being reduced by an amount proportional to this height ; and this is 

 not inconsiderable, as the following Table ( V) shows : — 



Table Y. 



District. 



Pumping, 

 station. 



Geological 

 formation. 



Difference 

 between 

 rest-level 



and work- 

 ing-level, 

 in feet. 



When 

 pumping, 

 gallons 

 per hour. 



Equivalent pres- 

 sure in lbs. per 

 square inch. 

 2-31 feet of water 



= presstcre of 

 lib. per sq. inch. 



Barnoldswick... 

 Birmingham . . . 



Hinckley 



St. Helen's 



Eyde 



Whitemoor. 



Perry Sink- 

 ing. 

 Snarestone. 



Kirkby. 



Knighton. 



Ashey. 



Itchell 

 Crondall. 



Millstone Grit. 



Triassic sand- 

 stone. 

 Do. do. 



Do. (Bunter). 



Lower Green- 

 sand. 

 Upper Chalk. 



Do. do. 



78 

 180 

 80 

 90 

 40 

 50 

 48 

 . 



15,000 



25,000 



7,500 



62,500 



16,700 



8,300 



8,300 



33-8 

 77*9 

 34-6 

 39-0 

 173 

 21-7 

 20-8 



Do 



Farnborough... 



