Pietenpol—Visible Spectrum of Wisconsin Lake Waters 575 
4500 5000 5500 6000 6500 
Fig. 5. Absorption curves for water from lake Waubesa, Aug. 11, 1915. 
1 and 2, filtered waters; 3, effluent. 
TABLE 2 
EFFECT OF TURBIDITY ON COEFFICIENT OF ABSORPTION 
Wave length 
Mendota 
Waubesa 
Filtered 
Effluent 
Unfiltered 
Filtered 
Effluent 
4700... 
.321 
.718 
1.761 
.5.30 
1.475 
4940. 
.259 
..590 
1..560 
.408 
1.290 
.5220. 
.222 
.485 
1.310 
.290 
1.0.30 
5890...... 
.209 
.444 
1.206 
.242 
.891 
5580.. 
.210 
.425 
1.156 
.2.55 
.828 
5790. 
.2.30 
.481 
1.160 
.276 
.815 
5895. 
.249 
.531 
1.182 
.281 
.838 
6005. 
.292 
.563 
1.220 
.309 
.858 
6180... 
.331 
.596 
1.2.50 
.320 
.878 
6360.... 
.381 
.614 
1.270 
.311 
.878 
6480... 
.410 
.614 
1.290 
.306 
.873 
6630... 
.418 
.614 
1.334 1 
.287 
.863 
6. Effect of Time on Color of Water 
During the course of this investigation observations were 
made to ascertain the effect of time upon a highly colored 
water. On Sept. 3, 1915, three samples of water from 
Turtle lake were brought to the laboratory and left standing 
in a dark place for different periods of time. The water was 
filtered in each case just before the selective absorption was 
