62 



EFFECTS OF WINDS AND OF 



TABLE No. 12. Principal facts for four final wind solutions. 



The probable errors of C p and C a as shown were computed rigorously from 

 the normal equations and the residuals of the observation equations. 



The probable error of a single observation as shown above is the probable 

 error, computed rigorously from the normal equations and the residuals, of 

 the observed change in elevation of the water surface at the gage in any one 

 hour. 



As indicated on page 57, in connection with an exposition of the meaning 

 of the quantities C p and C a , if C p and C a are equal there is no lag in the change 

 of elevation of the water surface at the gage behind the change in the wind 

 at the Weather Bureau station. If C p is finite and C a zero, the lag is 30 

 minutes, and if C p is zero and C a finite there is an anticipation of 30 minutes. 

 An examination of the values of C p and C a in table No. 12 shows that solution 

 W26 indicates a lag of 30 minutes, C a being practically zero; that solutions 

 W25 and W29 each indicate a lag of less than 30 minutes; and that solution 

 W20 indicates an anticipation or negative lag of much less than 30 minutes. 

 If one takes into account the degree of uncertainty indicated by the probable 

 errors, as well as the smallness of the indicated lag in each of the four cases 

 and the discrepancy between the four indications, the conclusion reached 

 is that the actual lag is probably less than 30 minutes and is too small to be 

 determined with reliability from the observations used. This conclusion 

 that the lag is less than 30 minutes, and certainly too small to be determined 

 from these observations, is confirmed by an examination of many details of 

 the evidence. 



In later portions of the investigation the lag in the wind effects was there- 

 fore assumed to be zero. All corrections for wind effect were computed on 

 that basis. On that basis the C x of the fundamental formula for wind effects 

 is C p +Ca. 



