Pietenpol—Visible Spectrum of Wisconsin Lake Waters 585 
rapidly in the shorter wave lengths, while G-reen and Marl 
lakes belong together, with an absorption which does not in¬ 
crease at all, or only very little for wave lengths shorter than 
55001. 
The same fact is shown in the lakes whose water was rated at 
8, as shown in fig. 9. Three of these lakes, Delavan, Geneva 
and Mendota, belong together, and have a great increase of 
absorption in the shorter wave lengths. Devils lake shows a 
Fig. 9. Absorption curves of lakes rated 8 on the color scale: 
1. Devils lake; 2. Lake Geneva; 3. Delavan lake; 4. Lake Men¬ 
dota. 
coefficient of absorption in this region quite as low as any of 
those rated at 6. Round lake is not shown on the diagram, 
but is found on fig. 13. It belongs to the same type as 
Devils lake in the relative absorption of shorter waves, but 
has a far greater coefficient of absorption at all wave lengths. It 
constitutes a peculiar case which is later discussed. 
The lakes rated at 14 also fall into two classes. Nagawicka 
and Otter lakes agree in having a rapidly rising absorption 
toward the blue end of the spectrum, while in Monona, Pine, 
