3 
This indicates that the ascending currents carried some of the oxygenless 
water from the bottom toward the surface, while beyond the influence of 
this vertical current the water descended carrying with it oxygen which it 
had received at the surface from the air. Both of these currents were more 
or less mixed with the water that normally lay at the different levels. 
The accompanying curves indicate the conditions in 1919 and also the con- 
ditions on the same date in 1912. 
The usual method of aerating stored waters is to spray the water into 
the air or allow it to flow over rubble or an interrupted spillway. The ad- 
vantage in the method just described is that it takes very much less energy 
to carry the air into the water than it does to force the water into the air. 
Figure 2. Broken lines are the curves for oxygen and temperature for 
September 25, 1912; the solid lines for September 20, 1919. T—=temperature 
Centigrade. O=cc. of oxygen per liter. Station I is at the air outlet. Sta- 
tion II is 150 ft. up the pond from Station T. 
