34 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
lake affected the minimum thermometer the thermometer was 
later placed in a water gauge and subjected to various pressures 
of air up to fifty pounds per square inch. Under the conditions 
of the experiment the effect on the thermometer varied from the 
tenth of a degree for fifty pounds to a degree for fifty pounds, 
with an average rise of thirty-five hundredths of a degree for the 
five best determinations. This would give a correction of forty- 
three hundredths of a degree to be subtracted from the reading 
of fifty-six degrees Fahrenheit obtained for the deepest place 
in the lake, 135 • feet, as recorded a year ago. In the present 
records of lake temperature this correction is not included. (It 
applies only to those of the twenty-sixth of July.) 
The maximum and minimum temperatures on the porch were 
obtained by the use of the ordinary maximum and minimum ther- 
mometers such as are used by the Weather Bureau. The mini- 
mum thermometer is subject to an additive correction of half 
a degree, which is here included in the data used. The maximum 
thermometer requires no correction. 
To record fluctuations in the level of the lake the same ap- 
paratus was used as last year, consisting of a cylindrical float in 
a larger cylinder pierced with a few nail holes. On the upper 
end of the float was a pen that traced a line on a revolving 
cylinder. 
GENERAL CONDITIONS. 
For study of the effect of wind pressure upon the general 
movement of water in the lake the opportunity for observation 
in July, 1916, was not as good as in July, 1915, when the wind 
was more variable and at times stronger than in 1916. The 
data on temperature are in some respects better than those ob- 
tained in 1915. Records were obtained in three different places 
with a view to comparing temperatures obtained north and south 
of the center of oscillation. 
The inflow from Spirit Lake seemed by inspection to be about 
equal to the outflow from Lower Gar Lake, as last year ; but 
the lake was four inches higher this year than last. 
FLUCTUATIONS UN LAKE LEVEL AT THE LABORATORY. 
The graph, not here reproduced, reveals a uniform fall in the 
surface due to evaporation, interrupted by occasional precipita- 
tion, the two about compensating each other the first and third 
