Figure 2. Tide with moon at extreme declination. 



Although the initial assumptions of equilibrium theory- 

 are invalid, i.e. there are large land masses, complex ocean 

 bathymetry and friction, nevertheless we do learn the im- 

 portant astronomical periods and the theoretical phases of 

 the tidal constituents. Hence we can imperically analyze 

 sets of tide observations for amplitude and phase lags 

 (called tidal harmonic constants). We can then synthesize 

 these same constituents (sum of a set of cosine curves) to 

 obtain tide predictions for another period. 



Traditionally this has been done on mechanical tide 

 prediction machines. Figure 3 shows the machine used by 

 the Coast and Geodetic Survey from about 1910 to I965. The 



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