A NEW EVAPORATION FORMULA 21 
(10), (11) and (12) are the same as equations (43), (44) and (45), respectively, in 
Publication No. 317, page 34. 
CHANGES IN DAILY BAROMETRIC CORRECTIONS 
The following formulas express the change in the barometric correction from 
one day to the next at the stations named : 
-1.78 &«,o-4.34 6*1-2.92 6^-0.90 6«8+1.99 6« +6.53 6^+6.34 6« 2 +2.03 6« 3 . . . .(14) 
At Harbor Beach: 
+2.81 6*0+5.29 6*1+5.10 6*2+0.68 bm- 1.00 6» -0.84 6 ni +0.49 6» 2 +0.47 6» 3 . . . .(15) 
At Mackinaw: 
-0.73 6*o-0.91 6*i-2.05 6*2-1.38 6* 3 +0.38 6» -2.89 6 ni -4.70 6 B2 -1.55 6» 3 . . . . (16) 
At Marquette: 
+ 1.03 6*o+1.50 6*i+2.20 6*2+0.61 6* 3 +0.56 6« +1.16 6m+1.67 6-2+1.37 6„ 3 . . . .(17) 
Equations (14), (15) and (16) are the same as equations (48), (49) and (50), 
respectively, in Publication No. 317, page 36. 
The definitions of bw , 6*i, 6*2, bus, &»o, &»i, bn 2 , bn 3 , for Lake Michigan-Huron 
are as follows, the current day being defined as the day to which the equation is 
assigned: 
6vo = (4 — 5) at 8 p. m. on the day before the day preceding the current day 
minus (4 — 5) at 8 a. m. on that preceding day. 
6*1= (4 — 5) at 8 a. m. of the preceding day minus (4 — 5) at 8 p. m. of that day. 
6*2 = (4 — 5) at 8 p. m. of the preceding day minus (4—5) at 8 a. m. of the 
current day. 
6*3= (4 — 5) at 8 a. m. of the current day minus (4 — 5) at 8 p. m. of the current 
day. 
6n =(3 — 6) at 8 p. m. on the day before the day preceding the current day 
minus (3 — 6) at 8 a. m. on that preceding day. 
6»i= (3 — 6) at 8 a. m. on the preceding day minus (3 — 6) at 8 p. m. of that day. 
6« 2 =(3 — 6) at 8 p. m. of the preceding day minus (3—6) at 8 a. m. of the 
current day. 
bn 3 = (3 — 6) at 8 a. m. of the current day minus (3 — 6) at 8 p. m. of the current 
day. 
The quantity (4 — 5), as in the equations for hourly effects, is the barometric 
pressure at the point marked 4 on Plate 2, minus the barometric pressure at the 
point marked 5 on that plate, in 0.01 inch of mercury. 
Similarly, (3 — 6) is the barometric pressure at the point marked 3 minus the 
barometric pressure at the point marked 6. 
For Lake Superior, (Marquette), the definitions of bw , bw ly . . . bw 3 , bn , 6»i, 
. . . 6«3, are the same as stated above except that (1—3) and (2—4) should be 
substituted for (4 — 5) and (3 — 6), respectively. 
The expressions, (14) to (17) inclusive, give the change in barometric correc- 
tion at the gages stated from one day to the next in units of 0.001 foot. The 
barometric correction is of opposite sign to the barometric effect. 
