18 THE TIDES; 



and slower, till, after three hours more, the flood- 

 tide has reached its greatest height, at which it 

 remains a short time without perceptible change. 

 The fall of the tide begins as slowly as the flow, 

 then the water retreats more quickly, and then 

 again more slowly ; and once more, after six hours, 

 the ebb has reached its lowest ; and there, again, 

 for a short time its level is kept unchanged. 



The sea rises and falls in this manner twice in 

 the day, or, more rightly, twice in the time that 

 passes between one epoch of the moon's crossing 

 the meridian and the next, which makes a period 

 of 1*035 day, or twenty-five hours nearly. Thus 

 the time of high water is later and later every day. 

 For instance, if it is high water to-day exactly at 

 noon, the flood will not be full to-morrow till one 

 o'clock in the afternoon, and so on; so that after 

 fourteen days we shall have high water again at 

 noon, and, when the moon has fulfilled one entire 

 journey round the earth, the third noon-day flood 

 comes up ; and thus the tides go on. 



The higher the sea rises during the flow of the 

 tide, the lower it falls during the following ebb. 

 The difference between the highest and lowest tide- 

 levels is very unequal on different coasts. In the 

 open ocean the rise of the tide is generally but 

 little. Thus at Otaheite the highest tides do 

 not rise more than eleven inches, and at the 

 Sandwich Islands, only two feet and a half; 



