A NEW EVAPORATION FORMULA 
43 
ber 5, there is a discrepancy of 0.026 foot between the barometric correction as 
computed by steps (1), +0.095, and (3), +0.121, respectively. This discrepancy is 
distributed proportionally to time (as shown in column 4) between the first and 
second selected day in such a manner as to make the discrepancy disappear on the 
second selected day, and all intermediate values are corrected as shown in column 
(5). This constitutes step (4), page 22. 
The values in column 5 are the final daily barometric corrections. They are 
applied to the observed elevation of the water surface, shown in column (6), to get 
the elevation corrected for barometric effects shown in column (7). 
Beginning at the second selected day, September 5, the computation is carried 
forward in the manner illustrated to the second selected day, September 15, and 
so on. 
The illustration just presented is for the Harbor Beach gage. In the same 
manner the mean daily observed elevations of the water surface at the other two 
gages on Lake Michigan-Huron, viz, Milwaukee and Mackinaw, and at the Mar- 
quette gage on Lake Superior, were corrected for barometric effects for each day of 
the 28 months of observation used in this investigation. 
There has thus far been illustrated in the Computation of Ii, step (a), page 33. 
EXAMPLE OF COMPUTATION OF WIND CORRECTION 
In addition to the barometric correction for each day for each gage, the observed 
elevation of the water surface was corrected for wind effects. The necessary formula 
and method are stated on pages 22 to 24. In order to expedite the computation 
of the daily wind effect a table, like Table 19 for Harbor Beach, was constructed 
for each gage. In this table Sh.b. is the value of S x for Harbor Beach shown in 
Table 9. The constant 0.0367 is the constant 0.088 of equation (18) multiplied 
by 10 to express the wind effects in units of 0.001 foot; and divided by 24, to convert 
the effect for each hour to the mean effect for the day. From this table it is seen 
that a wind from any direction of less than 22 miles per hour produces an effect on 
the daily mean water level of less than 0.001 foot, and it requires a wind of over 70 
Table 19 — Table for computation of wind effects, Harbor Beach 
Wind direction 
N. E. 
E. 
S. E. 
S. 
S. W. 
W. 
N. W. 
N. 
Sh.b. 
Sh.b.X0.0367 
-0.86 
- .0310 
-0.77 
- .0283 
-0.05 
- .00184 
+0.35 
+ .0128 
+0.86 
+ .0316 
+0.77 
+ .0283 
+0.05 
+ .00184 
-0.35 
- .0128 
Wind effect in 
units of 0.001 
ft. 
Wind velocity in miles per hour 

1 
2 
3 
4 
5 
to 21 
21 to 34 
35 to 42 
43 to 48 
49 to 53 
54 to 59 
to 22 
23 to 35 
30 to 44 
45 to 50 
51 to 50 
57 to 61 
0to70 
to 31 
32 to 50 
51 to 61 
to 21 
22 to 34 
35 to 42 
43 to 48 
49 to 53 
54 to 59 
to 22 
23 to 35 
30 to 44 
45 to 50 
51 to 56 
57 to 01 
to 70 
to 31 
32 to 50 
51 to 61 
Note: The wind effect is to raise the level of the water if the sign of Sh.b. is +. 
