114 



U. S. COAST AND GEODETIC SURVEY. 



directly obtained, in order to refer the f to the hour of the 1st 

 day of January, for the component Ssa the corrections will be twice 

 as great. 



If the year commences on the first day of any month other than 

 January, the corrections will differ a little from the above. Calculated 

 in a manner similar to that above, the following table gives the 

 correction to be applied to the f to refer to the first day of any 

 month at which the series commences. The correction to the f 

 of Ssa will be twice the tabular value for Sa. 



Observations commence — 



Jan. 1 

 Feb. 1 

 Mar. 1 

 Apr. 1 

 May 1 

 June 1 



observations commence — 



July 1 

 Aug. 1 

 Sept. 1 

 Oct. 1 

 Nov. 1 

 Dec. 1 



Correction to f of Sa 

 to refer to begin- 

 ning of month. 



Common 

 year. 



14.86 

 14.28 

 13.71 

 14.12 

 13.54 

 13.95 



Leap 

 year. 



15.19 

 14.69 

 14.20 

 14.69 

 14.20 

 14.69 



As the group summed covers approximately one-twelfth of the 

 period of the component Sa, or one-sixth of the period of Ssa, the 

 augmenting factors will be as follows: 



Sa 1.0115, logarithm 0.00497. 

 Ssa 1.0472, logarithm 0.02005. 



If the monthly means extend over many calendar years, it may be 

 convenient to combine them for a single analysis. In this case the 

 ( y^ _|_ ii) for January 1 may be taken as the average of the values for 

 the beginning of each year included in the observations, and the 

 correction to the T to refer to the beginning of the year will be a 

 mean of the values given above for common and leap years, weighted 

 in accordance with the number of each kind of year included. If 

 only a few years of observations are available, it is better to analyze 

 each year separately in order that the results may serve as a check 

 on each other. 



32. ANALYSIS OF HIGH AND LOW W^ATERS. 



The automatic tide gauge, which furnishes a continuous record of 

 the rise and fall of the tide, now being in general use, it is seldom 

 necessary to rely only upon the high and low waters for an analysis . 

 It may happen, however, that a record of high and low water observa- 

 tions is available for a more or less isolated locality where it has been 

 impractical to secure continuous records. Such records, if they 

 include all the high and low waters for a month or more may be 

 utihzed in determining approximate values of the principal harmonic 

 constants, but the results are not as satisfactory as those obtained 

 from an analvsis of the hourly heights. 



An elaborate mode of analvsis of the high and low waters is con- 

 tained in volume 1 of Scientific Papers, by Sir George H. Darwm. 

 Other methods are given by Dr. R. 4. Harris m his Manuai of Tides. 



