TIDAL DATUM PLANES 49 
Portland 
ae 
New York 
Atlantic City 
Charleston 
Mayport 
Fic. 23.—Daily sea level. at six Atlantic coast stations, October 1947. 
There appears to be an impression that sea-level changes are a function of the 
range of tide. That is, it is assumed that at stations where the range of tide is large, 
greater variations in sea level are to be expected than at stations having a small range 
of tide. That there is no basis for this impression, Figure 23 brings out as regards 
daily sea level. The average ranges of the tide at the six stations are as follows: Port- 
land, 8.9 feet; Boston, 9.5 feet; New York, 4.4 feet; Atlantic City, 4.1 feet; Charleston, 
5.1 feet; Mayport, 4.5 feet. At Boston, therefore, the range of tide is more than twice 
that at Atlantic City; nevertheless, the magnitude of the changes in daily sea level 
for the month shown is much the same. Indeed, for the last four days the changes at 
Atlantic City are somewhat larger. 
