MOVEMENTS OF UNDERGROUND WATER - 179 
sand at the outcrop allowed to absorb as much of the water as 
possible. Ten minutes after the water was turned on the water in 
the wells stood 1 foot below the escape pipe, indicating a rise of the 
water inthe wells of two inches. Occasionally air bubbles would 
escape at the intake, causing a slight fluctuation of the water in the 
wells. On opening well A and allowing the air to escape, the pressure 
of which was strong enough to force paper away from the mouth of 
the well, the water in the wells B, C, D, and E dropped back to its 
original level, 1 foot 2 inches below the escape pipe, thereby showing ~ 
that none of the water recently added to confine the air had reached 
the water table. 
The water in the pipe was now lowered to 2 feet 11 inches below 
the overflow pipe, the other conditions being the same as in the first 
test. Ten minutes after water was turned on, the head at wells B, C, 
D, and E was 2 feet 9 inches below the overflow pipe. The pressure 
on the confined air increases as the sand absorbs more water, and 
when the pressure becomes great enough some of the air rises through 
the sand and water and escapes at the outcrop. The instant a large 
bubble of air escapes there is a very slight drop in the water level in 
the wells. 
Thirty minutes after the water was turned on the water in the 
wells B, C, D,and E, stood 2 feet 8.5 inches below the escape pipe, 
indicating a rise of 2.5 inches. On opening well A and allowing 
the confined air to escape the water in wells B, C, D, and E dropped 
back to 2 feet 11 inches, thereby indicating that none of the recently 
added water had been added to the water table. The rise of the 
water in the wells in both of these cases was therefore due to the con- 
fined air between the water table and the newly added water layer 
near the intake; a condition which to a greater or less degree pre- 
vails during every rain storm, when the water absorbed by the surface 
shuts in more or less air between the surface layer of water and the 
water table. The effect of this additional pressure upon the yield 
at springs or wells is evident. 
In a region of flowing wells like that of southern Wisconsin and 
northern Illinois where the porous beds are saturated with water and 
the water more or less ponded, the yield at any given well depends 
largely upon the conditions of the beds in the immediate vicinity of 
