582 Wisconsin Academy of Sciences, Arts, and Letters. 
carried out, the direct illumination or the light from the disc 
entirely overpowers the feeble rays reflected from suspended 
particles. Any scheme of determining the color of lakes which 
depends on color comparators or on the use of white discs low¬ 
ered into the water, practically eliminates from consideration 
that part of the color which is due to reflection from suspended 
particles. 
4500 4750 5000 5500 6000 6500 
Fig. 7. Typical absorption curves from table 5. The wave lengths are 
platted on the horizontal axis and the coefficients of absorption on the 
vertical axis. The curves are as follows: 1. Distilled water; 2. Marl 
lake; 3. Mouse lake; 4, Okauchee lake; 5. North lake, 1915; 6. Swamp 
near Trout lake; 7. Pond No. 1; 8. North lake, 1914; 9. Tutrle lake, 
1914; 10. TurtleUake, 1915. 
It must also be said that most of von Aufsess’ work was done 
on lakes which are not rich in plankton. His most transparent 
lakes show a coefficient of absorption quite as low as PietenpoPs 
most transparent filtered water. 
The general form of the absorption curves from the Wisconsin 
lakes is similar to that of those examined by von Aufsess. 
