214 



apparatus which promised to measure the evaporation accurately and at the same 

 time do several other things was devised, but it proved a failure because it could 

 not be well protected in rough weather and still maintain natural conditions. 

 The apparatus which we hope we shall be able to perfect is as follows: 



A glass jar 9 inches in diameter and 12 inches high with a small hole near the 

 bottom and open at the top is sunk into the lake to within two inches of its top. 

 When the water in the jar has reached the level of the lake water a tight rubber 

 stopper is inserted in the small opening from without. The column of water in 

 such a jar would be as near as possible under the same conditions as the surround- 

 ing water, and the fall of the water in the jar, plus the amount of rainfall for the 

 period, would very closely approximate the amount of evaporation. This appa- 

 ratus would also enable one to get at the amount of water received from springs 

 and other sources aside from rain falling directly into the lake. The amount of 

 reduction due to outflow from the lake can readily be calculated by observing the 

 outlet. Mr. Eidgley has estimated it at .0017 inches per day. If at the end of 

 thirty days there was a difference between the water in the jar and the water in 

 the lake, less the calculated reduction of the lake due to outflow, the difference 

 would represent the inflow from springs and other tributaries during thirty days. 



The lake is frozen over about four months in a year. During the remaining 

 eight months evaporation is going on at a maximum rate of one-fourth inch per 

 day and a minimun of 0. Taking one-eighth inch per day as the average, we 

 obtain about thirty inches as the amount of the annual evaporation. At this rate 

 the lake, if without income, would become dry in twenty-eight years. Four 

 years would reduce the lake to half its present size. 



Outflow and evaporation operating together would reduce the level at the fol- 

 lowing rate : 



Time in Years. 



Eeduction by 

 Outflow. 



Reduction by 

 Evaporation. 



Total Eeduction. 



3 

 3 



2 



2 

 2 

 1 

 1 about 



1 ft. 9 in. 

 4 



3 2 



4 8 

 6 8 



5 2 

 17 7 



7 ft. 6 in. 



7 6 



5 



5 



5 



2 6 



2 6 



9 ft. 3 in. 

 11 6 



8 2 



9 8 

 11 8 



7 6 

 10 1 



14 



33 2 



35 



68 



