A NEW EVAPORATION FORMULA 
13 
In the computation of the outflow from Lake Michigan-Huron, the diversion at 
Chicago was added to the quantity obtained from equation (G). On Lake Michi- 
gan-Huron, 0.001 foot of depth per day is equivalent to 14,050 cubic feet per second, 
therefore the diversion at Chicago was taken as 0.0005 foot per day and constant, 
with sufficient accuracy for this purpose. 
RAINFALL ON THE LAKE (/ 2 ) 
The rainfall on the lake area was assumed to be the same as that observed at 
the shore stations nearest the lake. 1 All of the rainfall stations existing at the time 
covered by the data used in this investigation, 1909 to 1913 inclusive, were used, 
including both the regular U. S. and Canadian Weather Bureau stations and the 
stations maintained by cooperative observers. The rainfall of each station was 
weighted according to the proportion of lake area adjacent to it. The complete 
list of rainfall stations used for Lake Michigan-Huron is shown in Table 3 and on 
Plate 1. The corresponding complete list of rainfall stations for Lake Superior is 
shown in Table 4 and on Plate 4. 
Table 4. 
-Rainfall stations, adjacent areas, and factors for converting rainfall in inches of depth to units of 
0.0001 foot rise of surface of Lake Superior 
Station 
Lake area 
adjacent 
to station 
Factor 
Station 
Lake area 
adjacent 
to station 
Factor 
Two Harbors, Minn 
(sq. mi.) 
721 
73 
139 
3,829 
127 
1,844 
569 
3,974 
236 
1 885 
18.81 
1.96 
3.67 
99.61 
3.36 
48.00 
14.85 
103.38 
6.20 
Chatham, Mich 
(sq. mi.) 
82 
637 
3,449 
3,096 
153 
1,221 
5,180 
1,025 
3,768 
2.19 
16.62 
89.73 
80.55 
4.04 
31.81 
134.74 
26.71 
98.03 
Duluth, Minn 
Munissing, Mich 
Superior, Wis 
Grand Marias, Mich 
Bayfield, Wis 
Whitefish Pt., Mich 
Deer Park, Mich. . . 
Ashland, Wis 
Houghton, Mich 
Calumet, Mich 
Schreiber, Canada 
Port Arthur, Canada 
Eagle Harbor, Mich 
Baraga, Mich. . . 
Isle Royal, Canada 
Total 19 St 
itions 
32,008 
833.33 
Note — Factor = a/Ax , in which a is the lake area adjacent to a rainfall station, A is the area of Lake 
12 
Superior, viz, 32,000 square miles, and the factor converts observed rainfall at a station in inches of depth to units 
of 0.0001 foot rise of surface of Lake Superior. The best available value of the area of Lake Superior at the 
time these factors were computed was 32,060 square miles, as given on page 9 of "Report of the International 
Waterways Commission on Regulation of Lake Erie" (1910). In "Diversion of Water from the Great Lakes and 
Niagara River" (1921), page 367, the area is given as 31,810 square miles. 
RAINFALL ON LAND DRAINAGE AREA ADJACENT TO LAKE (RELATED TO h) 
The estimate of the constant part of the run-off into each lake from its adjacent 
land drainage area, the I c of equation (1), involved a knowledge of the rainfall on 
that land drainage area. Each rainfall station for estimating the rainfall on land 
was weighted in proportion to the land area adjacent to it. The complete list of 
rainfall stations used in this investigation for estimating the rainfall on the land 
part of the drainage area of Lake Michigan-Huron is given in Table 5 and the 
locations of these stations are shown on Plate 1. Note that the stations near the 
'The accuracy of this assumption was tested by a series of least-square solutions. The method used, and 
results obtained, are not presented for want of space. Briefly, it may be said that, the departure — if any — of the 
assumption from the truth could not be detected from the observations by the method employed. 
