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PACIFIC SCIENCE, Vol. XV, October 1961 
Fig. 42. Diagram showing number of times each month during 1953 various levels in the intertidal zone 
were exposed. 
38-41). Twice a month there are two tides a 
day which are about equal, and in the intervals 
between there is a much greater inequality in 
the height of any two successive low waters than 
between the two high waters of the same day. 
During the summer months (Fig. 40) the low- 
est low waters occur during daylight hours and 
during the winter months (Fig. 41) the lowest 
low waters occur late at night or early in the 
morning. 
The number of times during the year when 
each of the various levels recognized (Fig. 39) 
are exposed is indicated in Figure 42, and the 
number of days of continuous exposure of the 
