64 EFFECTS OF WINDS AND OF 



column is the W of formula (69), namely, the value in the sixth column of 

 the table multiplied by +0.088. 



The mean of the 24 values of W for August 5, 1910, at Buffalo gage, as 

 shown in the last column of table No. 11, is +0.258 foot, which is therefore 

 the daily wind effect for that day. The daily wind effects might be so 

 computed. 



Merely as devices to save time in the computation of daily wind effects, 

 it was found to be advisable to make two changes in the method of computa- 

 tion which is indicated above. One change was to construct a table for 

 each gage, giving the values of W in terms of the two arguments, wind 

 velocity and wind direction. Note that in formula (69) there are only two 

 variables in the second member, the wind velocity, h, and S*, which is 

 variable for a given gage as a function of the wind direction only. The 



W 

 other change was to make the actual values placed in this table instead of 



ATE 



W itself. With the table before one and with the observed wind velocity 

 and direction for each hour also before one, the tabular values, one for each 

 hour, could be taken out very rapidly to the nearest thousandth of a foot. 

 The sum of the 24 tabular values for any day was the daily wind effect. No 

 division by 24 was necessary, as would otherwise have been the case, be- 

 cause each tabular value was itself the result of such a division. 



ACCURACY OF COMPUTED BAROMETRIC EFFECTS. 



Having set forth the theory and the methods of computation by which 

 the formulae and constants for computing barometric effects and wind effects 

 have been determined, it is now proposed to set forth the main portions of the 

 available evidence as to the accuracy and reliability with which the baro- 

 metric effects and wind effects may be computed by the use of these formulae 

 and constants. 



It is the purpose to set forth the evidence, first, in connection with the 

 computed barometric effects; second, in connection with the computed 

 wind effects; and, third, as to the overall accuracy attained when corrections 

 are applied to each day's observations at each gage for both barometric and 

 wind effects. 



Let the evidence be considered here as to the accuracy of the computed 

 barometric effects. 



Table No. 6, page 32, shows each of the values of the various barometric 

 constants B wQ , B w i, etc., and its probable error as computed rigorously from 

 the normal equations and the residuals of the least-square solution. These 

 probable errors are a measure of the accuracy which is the best that can be 

 obtained, provided the errors in the derived constants are all accidental in 

 character. Assuming that the errors are all accidental, that is, that there 

 are no systematic or constant errors affecting the final results, it is an even 

 chance that the actual error in any constant is greater than or less than its 



