1912] GLEASON & GATES—RATES OF EVAPORATION 481 
reading of 15 feet above the zero of the Havana gauge, located 
about 2.5 km. south. The lake has a continuous connection with 
the Illinois River, forming an expanse of water about 400 m. wide. 
During the course of the experiment the river fell from 12 to 7.8 
feet on the Havana gauge. The location of the atmometer was 
selected to show the evaporation from an open surface near the 
Fic. 1.—Atmometers in process of standardization, June 22, 1910; photograph 
by F. C. Gates. 
water. The ground is sandy and for the most part without vegeta- 
tion because of its regular inundation during high water in the 
river. The plants that occur along the beach are mostly sand 
plants, such as Sporobolus cryptandrus, Cenchrus carolinianus, and 
Opuntia Rafinesquii. There are some relics from the mixed forest 
above, as Clematis Pitcheri, and numerous xerophytic weeds, as 
Melilotus alba. A few trees still grow at the water’s edge, but most 
of the original shore vegetation has succumbed to the effect of the 
higher average level of the water since the opening of the Chicago 
