36 EFFECTS OF WINDS AND OF 



barometric effects have been computed as a rule without the insertion of 

 maximum and minimum points, in the belief that the possible gain in ac- 

 curacy thereby sacrificed is negligible. 



The separate values of N-S effect and of E-W effect, and their sum E it 

 the total barometric effect, were computed from formula (43). Note that 

 the computed maximum barometric effect occurred at noon on September 24 

 corresponding to the value +40 in the column headed (3-6). 



To obtain hourly elevations of the mean surface of Lake Michigan- 

 Huron from observed hourly elevations of the water surface at Milwaukee, 

 one must subtract the barometric effect for each hour computed as shown in 

 the example. 



COMPUTATION OF DAILY BAROMETRIC EFFECTS. 



The mean of the 24 hourly barometric effects for any day is the best 

 value obtainable for the daily barometric effect. 



To obtain daily elevations of the mean surface of Lake Michigan-Huron, 

 one must subtract the daily barometric effect for each day from the mean of 

 the 24 hourly elevations of the water surface at Milwaukee for that day. 



To compute the barometric effect for each day by first computing the 24 

 hourly barometric effects for that day and then taking the mean is an un- 

 necessarily slow and laborious procedure. The method of computation 

 indicated below is much more rapid and is believed to be but slightly less 

 accurate. 



In the formula for the observation equations as shown in (40), page 24, 

 the first eight terms b u , B u , , b wi B w \ . . . 6 2 B n2 , b n s B n s express the 

 change in barometric effect from one day to the next. The quantities 

 B w o, B w i, . . . B nZ , B nS have been determined by the least-square solu- 

 tions, and their values are shown, for each of five stations, in table No. 6, 

 page 32. Therefore, the following formulae express the change in the baro- 

 metric effect from one day to the next at the stations named : 

 At Buffalo 



- 2 . 226^0 + 3 . 85&ua + 5 . 966 w2 + 1 . 85& w3 - 3 . 966 n0 



- 10. 786 n i-l 1.696ns- 4. 82& n3 (46) 

 At Cleveland 



+0.696 WO +1 . 226 w i+l 046^+1 . 306*3+ 1 . 736 n0 



+4 . 236 nl +6 . 046 n2 + 1 . 606 n3 (47) 

 At Milwaukee 



- 1 . 786u, - 4 . 346 wl - 2 . 92b wZ - . 906*3 + 1 . 996 n0 



+6 . 53& n i +6 . 346 n2 +2 . 036 nS (48) 

 At Harbor Beach 



+2. 816,o+5. 296 ir i+5.106 ttS +. 686^,3 -1.006 B o 



-.84& nl +.496 n2 +.476 n3 (49) 

 At Mackinaw 



-0.736*0-. 916 u ,i-2.05& u , 2 -1.386 u ,3+.38&no 



-2.896Bi-4.706n2-l.556,,, (50) 



