40 
A NEW METHOD OF ESTIMATING STREAM-FLOW 
values as taken from the charts. The other values in these columns, the figures en- 
closed in square brackets, are the hourly differences in pressure obtained by linear 
interpolation between the observed 8 a. m. and 8 p. m. differences, on the assump- 
tion of uniform change in pressure between those two times. Columns 8 and 9 are 
computed from equation (11), the "N-S Effect" and "E-W Effect" being, re- 
spectively, the products (3-6) ( — 0.44) and (4-5) (+6.94), proper attention being 
paid to the lag of 6 hours in each case. The total effect, E x , for any hour, is the sum 
of the two separate effects for that hour. The mean effect for the day, —0.095 
Table 16— Example of computation of hourly barometric effects, Harbor Beach 
Date and hour 
Barometric pressure at point — 
N-S 
effect 
E-W 
effect 
total 
effect 
3 
6 
4 
5 
(3-6) 
(4-5) 
1910 
Sept. 4 
in. 
29.90 
in. 
29.85 
in. 
29.85 
in. 
29.95 
in. 
+0.05 
[+ -09] 
+ .09 
[+ -10] 
[+ -10] 
[+ -10] 
[+ -11] 
[+ -12] 
[+ -12] 
[+ -12] 
[+ -13] 
[+ -14] 
[+ -14] 
[+ -14] 
+ .15 
[+ -14] 
[+ -14] 
[+ -14] 
[+ .13] 
[+ -12] 
[+ -12] 
[+ -12] 
[+ -HI 
[+ -10] 
[+ -10] 
[+ -10] 
+ .09 
in. 
-0.10 
[- -12] 
- .12 
[- -12] 
[- -12] 
[- -12] 
(- -13] 
[- -13] 
[- -13] 
[- -13] 
[- -13] 
[- .14] 
[- -14] 
[- .14] 
- .14 
[- -14] 
[- -14] 
[- -13] 
[- -13] 
[- -13] 
[- -12] 
[- -12] 
[- -12] 
[- .12] 
[- -12] 
[- -11] 
- .11 
ft. 
ft. 
ft. 
8 
9 
29.93 
29.84 
29.83 
29.95 
10 
11 
Sept. 5: 
0.00 
.00 
.00 
.00 
.00 
.00 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
- .01 
.00 
.00 
.00 
-0.08 
- .OS 
- .08 
- .08 
- .08 
- .09 
- .09 
- .09 
- .09 
- .09 
- .10 
- .10 
- .10 
- .10 
- .10 
- .10 
- .09 
- .09 
- .09 
- .08 
- .08 
- .08 
- .08 
- .08 
Mean 
-0.08 
- .08 
- .08 
- .08 
- .08 
- .09 
- .10 
- .10 
- .10 
- .10 
- .11 
- .11 
- .11 
- .11 
- .11 
- .11 
- .10 
- .10 
- .10 
- .09 
- .09 
- .08 
- .08 
- .08 
- .095 
2 
3 
4 
6 
6 
7 
8 
9 
29.92 
29.77 
29.77 
29.91 
10 
11 
2 
3 
4 
5 
6 
7 
8 
9 
29.89 
29.80 
29.78 
29.89 
10 
11 
foot, is the amount by which the water at the gage at Harbor Beach was forced 
down by the existing barometric pressures for that day below the mean elevation of 
the whole lake surface for that day as determined from the Harbor Beach gage 
reading. Hence, to obtain the mean elevation of the whole lake surface for that 
day, in so far as it can be determined from the reading on this gage alone, corrected 
for only barometric effects, the observed elevation at the gage is corrected by 
4-0.095 foot. 
Thus far, in the two preceding paragraphs, there has been illustrated step (1), 
page 22. The value +0.095 is shown in parentheses in the third column of Table 
