34 EFFECTS OF WINDS AND OF 



For Cleveland, EI, for any hour = (6-8) (+2. 12) + (5-7) (+6.80), in (42) 

 which (6-8) must be taken for 4 hours earlier and (5-7) 

 for 2 hours earlier than the hour for which the effect is 

 being computed. 



For Milwaukee, EI, for any hour = (4-5) ( -4 . 97) + (3-6) (+8 . 44) , (43) 

 in which (4-5) must be taken for 7 hours earlier and (3-6) 

 for 4 hours earlier than the hour for which the effect is 

 being computed. 



For Harbor Beach, EI, for any hour = (4-5) (+6. 94) + (3-6) (44) 

 (0.44), in which (4-5) must be taken for 6 hours earlier 

 and (3-6) for 6 hours earlier than the hour for which the 

 effect is being computed. 



For Mackinaw, E 1} for any hour = (4-5) ( - 2 . 54) + (3-6) ( - 4 . 38) , (45) 

 in which (4-5) must be taken for 2 hours later and (3-6) 

 for 1 hour later than the hour for which the effect is being 

 computed. 



The example on page 35 shows the details of the computation of hourly 

 barometric effects at Milwaukee on September 24, 1910. The barometric 

 effects at Milwaukee on this day were unusually large and were changing 

 with unusual rapidity. 



It was especially desirable to secure the hourly barometric effects on 

 September 24 with as great accuracy as possible, because this was one of the 

 dates used in a computation of wind effects at Milwaukee. Hence, a 

 special study of the forecast maps of this and adjacent days was made with a 

 view to determining the time of maximum and minimum pressure at each 

 reading point and the value of each such maximum or minimum. Within 

 the limits shown in the example there are six points found by this special 

 study, namely: 



A maximum of 30.34 at 9 p.m. on Sept. 23 at point 3, 

 A maximum of 30. 10 at 9 p.m. on Sept. 23 at point 6, 

 A maximum of 30.26 at 3 a.m. on Sept. 24 at point 5, 

 A minimum of 29.80 at 11 a.m. on Sept. 24 at point 6, 

 A minimum of 29.80 at 5 p.m. on Sept. 24 at point 4, 

 A minimum of 29.79 at 11 p.m. on Sept. 24 at point 3. 



Each of these maxima and minima is inclosed in a parenthesis in the 

 example of computation given. 



Consult plate 2 for the location of the points 3, 4, 5, and 6 for which the 

 barometric pressures were read from the forecast maps. 



Opposite each maximum or minimum the pressure as given in square 

 brackets for the companion point was obtained by interpolation between the 

 next preceding and next following value at that point, on the assumption 

 that during the interval the pressure changed at a uniform rate. 



The values in the columns (3-6) and (4-5) which are not included in 

 square brackets were obtained directly by subtraction from the preceding 



