574 Wisconsin Academy of Sciences^ Aris^ and Letters. 
put through a centrifugal machine and filter papers and the 
unfiltered lake water was just as brought into the laboratory. 
It had been strained through a silk net of No. 20 bolting cloth, 
which removed the Crustacea, larger algae, etc., but left the 
nannoplankton in the water. The corresponding slopes of 
the curves as shown in fig. 4 indicate most conclusively that 
the absorption by particles is nonselective in nature. Similar 
absorption curves for the filtered water and effluent of lake 
Waubesa are shown in fig. 5. 
4500 5000 5500 6000 6500 
Fig. 4. Absorption curves for water from Lake Mendota, Aug. 16, 1915. 
1. 'Water filtered through Berkefeld filter; 2. “Effluent,” i. e. water 
passed through a De Laval centrifuge and filter, which extracts most 
of the suspended matter by centrifugal force and by filter papers; 3. 
Lake water strained through silk bolting cloth and containing all of the 
nannoplankton. 
In this and following figures the wave lengths are platted on the hor¬ 
izontal scale, and the coefficient of absorption on the vertical 
scale. 
