41 



76. Other components. — Additional small components disclosed by 

 the mathematical analysis later outlined are here appended for 

 convenient reference. 



Table III 



Symbol 



2N 



vzCnu) 



Xs (lambda) 



Ai2(mu) 



00 



2Q 



Pi(rho) 



MSf 



Name 



Lunar elliptic, 2d order, semidiurnaL. 

 Larger lunar evectional, semidiurnaL, 

 Smaller lunar evectional, semidiurnal 



Variational 



Lunar diurnal, 2d order 



Lunar elliptic, 2d order, diurnal 



Larger lunar evectional, diurnal 



Lunisolar synodic, fortnightly 



Speed 



27.895,354,8 

 28. 512, 583, 1 

 29. 455, 625, 3 

 27.968,208,4 

 16.139,101,7 

 12. 854, 286, 2 

 13.471,514,5 

 1.015,895,8 



HARMONIC ANALYSIS OF TIDES 



77. The amplitude and initial phase of each component of the tide 

 at any tidal station may be computed from the observed hourly tidal 

 heights for a sufficient period of days, and the predetermined speed 

 of the component, by the process of harmonic analysis, which will now 

 be explained. The observed heights used for this computation are 

 taken at (mean solar) hourly intervals, beginning at midnight (0 hour) 

 each day, giving 24 observations per day. The observations ordi- 

 na;rily are on standard time; but early records may be on local time. 



78. Separation of S group of components. — The repeating form of 

 the sinusoidal curve representing any component (fig. 16) shows at 

 once that the value of the component at any instant is repeated at the 

 intervals of time given by the period of the comi3onent, and by any 

 multiple of that period. Thus since the period of the So component 

 is 360°/30°=12 hours, this component has exactly the same value at 

 say 3 p. m. on any day as at 3 a. m. ; and has the same value at 3 a. m. 

 on every succeeding day. The solar overtides S4 and Se, with periods 

 of 6 hours and 4 hours respectively, each have similarly the same value 

 at the same hour each succeeding day, as has the small Si component. 

 All other components have values which progressively vary at the 



