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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 34 



most places in the world, the tide here comes about the same time 

 day after day. That this is not a general feature of the tides in 

 the South Pacific Ocean is evident from a comparison with the tide 

 curves for Apia, Samoa, for the same week, which are shown in 

 figure 6. It will be noted that here there is a distinct shift to the 

 right in regard to the times of high and low water in following down 

 the curves. 



Feet 



Figure 6.^ — Tide curves, Apia, Sept. 10-16, 1925. 



The mathematical process of harmonic analysis permits the tide 

 at any place to be resolved into its simple constituent tides. At 

 Apia the principal lunar constituent has a range of 2.5 feet, while 

 the principal solar constituent has a range of 0.6 foot. Hence the 

 tide here follows the moon. At Tuesday Island, the principal lunar 

 and solar constituents both have the same range of 3.1 feet. Hence 

 here the tide is no longer predominantly lunar but as much solar as 

 lunar. 



The answer to the question as to why the tide at some places is 

 governed by the sun rather than the moon is again found in the physi- 

 cal characteristics of the various oceanic basins and seas. Where the 



