32 THE TIDES. 



is called tlie Establishment of the Port. The 

 knowledge of this time is very important to the 

 sailor, because from this he can reckon at what hour 

 on that or on any other day he can run into a 

 harbour, where the rise and fall is great, without 

 danger, and with the advantage of the tide. 

 Whewell has remarked, in regard to this, that 

 in open channels, such as the British, the flood- 

 stream continues to run for some time (even as 

 much as three hours) after high-water, and that 

 in the same manner the ebb-stream does not cease 

 at the time of low water, but continues for a certain 

 time longer, which varies according to circum- 

 stances, lasting in the Channel till the half tide. 

 This arises from the fact, that the water-level in 

 the English Channel has become much raised, 

 during the flow of the tide, above that of the 

 North Sea, and, on the other hand, during the ebb 

 has fallen considerably below it. 



