82 U. S. COAST AND GEODETIC SURVEY 
sponse to the changes in phase and parallax of the moon are very small, the primary 
variation depending on the moon’s declination. 
The daily height of high water is thus subject to relatively large variations both 
periodic and nonperiodic in character. The periodic variations depend primarily on 
the phase, distance, and declination of the moon, the periods of these being approxi- 
mately 29%, 27%, and 27% days, respectively. Such variations are therefore largely 
eliminated within a month. And within a month, too, the large variations in sea 
level due to wind and weather tend to balance out. It follows therefore that monthly 
high waters will show smaller variations than daily high waters. 
Monthly High Water 
In Figure 40 are shown the monthly heights of high water at the same three 
stations as in Figure 38 for the 2-year period 1946-1947. From one month to the 
next, high water is seen to vary from a few hundredths of a foot to as much as 0.8 foot. 
1946 1947 
Jan. Apr. July Oct. Jan. Apr. July Oct. Dec. 
Atlantic City 
Los Angeles 
Pensacola 
Fic. 40.—Monthly heights of high water, Atlantic City, Los Angeles, and Pensacola, 1946-47. 
