171 
was 32°-96°. The highest temperature recorded in the river 
was 89°, on the afternoon of August 3, 1897, and again, at the 
same time of day. July 26, 1598. 
The diurnal range in temperature is considerable at times, 
depending naturally upon that of the air. On August 3-5,1598, 
in connection with a test of the diurnal movements of the 
plankton and accompanying analysis of the gases dissolved in 
the water, the temperatures recorded indicate in the surface 
waters a range of 5.5°, with a maximum of 79.5° at 5:00 p.m, 
and a minimum of 74° at 2:00 a. m. The bottom water (depth 
2.44 meters) showed a range of but 2°, from 74° at 8:00 a. m. 
to 76° at 11:00 a.m. The air temperatures on the days in ques- 
tion ranged from 83° at 5:00 p.m. to 58° at 5:00 a.m. A diur- 
nal variation of 5.5° in surface waters and 2° in bottom waters 
is thus indicated at this time. Other conditions will probably 
show a slightly greater range. 
MONTHLY AND YEARLY AVERAGES OF SURFACE TEMPERATURES, 1[894-1899, 
ILLINOIS RIVER. 
| Ray 
Year | Jan. | Feb. Mar.|April] May |, June} July | Aug.|Sept.| Oct. | Nov.| Dec. sz 
> 
Pea ee al ee a eae aoe 80. 25/82.25|83.5 \77.5 |58 al Se see 
TOQ5 accis||e2-3' Qi a Wieossis 58 -. (80 79 — |80.51)78.87)54.26.42.5 |37-5 |..---- 
1896... .|32-75]33.7 |39-52/64.54|72.7 |74-7 |80.7 |82 [65.75/56 |44 133-6 |56.66 
133 ¥/eoba) bacor 32.25/43.8 |60  |66.3 |75 _ |81.02'80.9 |77.07/65.1 |45.7 |33-02)...... 
1898. ...|32-7 |32-12/43.3 |53-32/65.8 |78.8 [82.87 80. 56/71.87/54.37 41-42 32.98/55 -84 
1899...-132-9 {32-6 135.2 |...-.|----- eae el (eae [otk jiitee [ee eee eet eek 
Monthly if 
average|32.78)32-73 40-45|60. 46/68. 27/77 .75|81 -03/81 . 49174 -21/57-55143-00 35 -22'57 .08* 
*Average of monthly averages. 
The temperature records are too isolated to plot complete 
thermographs of the river and its backwaters, though they do 
give a very fair idea of the seasonal fluctuations, especially in 
the later years, when they were more evenly distributed, and 
in the midsummer, when they were more numerous. They were 
usually taken between 7:00 a.m. and 5:00 p. m., and may be 
regarded as day temperatures. A comparison of the records in 
Table III., the plottings (Pl. VIII.—XIII.), and the above table, 
giving the monthly.averages of surface temperatures of our 
records, shows the following seasonal routine in the river: 
