142 U. S. COAST AK"D GEODETIC SURVEY. 



36. FORMS USED FOR ANALYSIS AND PREDICTIONS. 



The forms used by the U. S. Coast and Geodetic Survey to faciHtate 

 the work of the harmonic analysis and predictions of the tides, 

 together with an example of their use, are shown in Figures 22 to 34. 

 A series of tidal observations at Morro, Calif., for February 13 to 

 July 25, 1919, is taken as the example to illustrate the analysis and 

 the computation of the settings for the predicting machine. 



Form 362, hourly heights (fig. 22) . — The hourly heights of the tide 

 are first tabulated in Form 362. Although the zero of the tide staff 

 is usually taken as the height datum, any other fixed plane will serve 

 this purpose. For practical convenience it is desirable that the 

 datum be low enough to avoid negative tabulations, but not so low 

 as to cause the readings to be inconveniently large for summing. 



The hours refer to mean solar time, which may be either local or 

 standard, astronomical or civil, but standard civil time will generally 

 be the most convenient to use. The series must commence with the 

 zero (0) hour of the adopted time, and all vacancies in the record 

 should be filled by interpolated values in order that each hour of the 

 series may be represented by a tabulated height. It is the general 

 practice to use red ink for the interpolated values to distinguish 

 them from the observed heights. The record for successive days of 

 the series must be entered in successive columns of the form, and 

 these columns are to be numbered consecutively, beginning with one 

 (1) for the first day of the series. 



The series analvzed should be one of the following lengths: 1.5 (14 

 days for diurnal components), 29, 58, 87, 105, 134, 163, 192, 221, 250, 

 279, 297, 326, 355, or 369 days. Series of observations very nearly 

 equal to one of these standard lengths may be completed by the use 

 of extrapolated hourly heights. If the observations cover a period 

 of several years, the analysis for each year may be made separately, a 

 comparison of the results affording an excellent check on the work. 



The hourly heights on each page of Form 362 are first summed 

 horizontally and vertically. The total of the vertical sums must 

 equal the total of the horizontal sums, and this page sum is entered in 

 the lower right-hand corner of the page. 



Stencils (figs. 23 and 24). — The first figure is a copy of the com- 

 ponent M stencil for the even hours of the first seven days of the 

 series, and the latter illustrates the use of the same. This stencil 

 being laid over the page of hourly heights shown in Figure 22, the 

 heights applying to each of the even component hom^s for this page 

 show through the openings in the stencil, where they appear con- 

 nected by diagonal lines, thus indicating each group to be summed. 



For each component summation, excepting for S, there are pro- 

 vided two stencils for each page of tabulated hourly heights, one for 

 the even component hours and the other for the odd component hours. 

 The stencils are numbered with the days of series to which they 

 apply, and special care must be taken to see that the days of series 

 on each stencil correspond with the days of series on the page of 

 tabulations with which it is used. 



For component iS no stencils are necessary, as the component hours 

 correspond to the solar hours of the tabulations, and the horizontal 

 sums from Form 362 may be taken directly as the component hour 

 sums. 



