1900 



r- 



1910 



1920 



TIME(yr) 



1930 1940 



1950 



1960 



1970 



Yakutot , Alaska 



r20 



-15 



10 



•-0 



Canal Zone 



Figure 7. Change in sea level with respect to adjacent land for Yakutat, 

 Alaska, Honolulu, Hawaii, and Cristobal, Canal Zone (National 

 Oceanic and Atmospheric Administration, 1974). 



III. THE TIDE PREDICTION EQUATION 



The astronomical tide results primarily from the interaction of the gravitational fields of 

 the Eartli, Moon, and Sun. The gravitational tide-generating force can be expressed, with 

 any desired accuracy, as the sum of a number of periodic terms, determined from the 

 astronomical parameters pertaining to the orbit of the Moon around the Earth, and the 



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