BAROMETRIC PRESSURES ON THE GREAT LAKES 



35 



columns. The values in these columns which are inclosed in square brackets 

 were obtained by interpolation from the unbracketed values in the same 

 columns, on the assumption that the rate of change of the barometric 

 gradient was constant during each interval between unbracketed values. 



Example of computation of hourly barometric effects Milwaukee. 



The insertion of the six maximum and minimum points, and of the 

 corresponding unbracketed values in the (3-6) and (4-5) columns, probably 

 gave a slightly increased accuracy to the computation for this particular day. 

 These maximum and minimum points can be determined with difficulty 

 and with but a small degree of accuracy from the forecast maps by studying 

 the rate and direction of progress of the isobars in each 12-hour interval. 

 Usually, the maxima and minima are poorly defined and differ but little 

 from the values which would be obtained by direct interpolation between the 

 preceding and following 8 o'clock values. For these reasons the hourly 



