GENERAL CHARACTERISTICS 15 



it is broken up, one wave-crest travelling up the English Channel, 

 while another flows round Scotland and then southwards into the 

 North Sea. 



The former branch, taking the shorter course, determines the 

 time of high tide along the Channel coast. Passing the Land's 

 End, it reaches Plymouth in about an hour, Torquay in about an 

 hour and a half, the Isle of Portland in two hours and a half, 

 Brighton in about seven hours, and London in about nine hours 

 and a half. The other branch, taking a much longer course, makes 

 its arrival in the southern part of the North Sea about twelve 

 hours later, thus mingling at that point with the Channel wave 

 of the next tide. It takes about twenty hours to travel from the 

 south-west coast of Ireland, round Scotland, and then to the mouth 

 of the Thames. Where the two waves meet, the height of the 

 tides is considerably increased ; and it will be understood that, at 

 certain points, where the rising of one tide coincides with the falling 

 of another, the two may partially or entirely neutralise each other. 

 Further, the flow and the ebb of the tide are subject to numerous 

 variations and complications in places where two distinct tidal 

 wave-crests arrive at different times. Thus, the ebbing of the tide 

 may be retarded by the approach of a second crest a few hours 

 after the first, so that the ebb and the flow do not occupy equal times. 

 At Eastbourne, for example, the water flows for about five hours, 

 and ebbs for about seven and a half. Or, the approach of the 

 second wave may even arrest the ebbing waters, and produce 

 a second high tide during the course of six hours, as is the case 

 at some places along the Hampshire and Dorset coasts. 



Those who visit various places on our own coasts will probably 

 be interested in tracing the course of the tidal crests by the aid of 

 the accompanying map of the British Isles, on which the time of 

 high tide at several ports for the same time of day is marked. It 

 will be' seen from this that the main tidal wave from the Atlantic 

 approaches our islands from the south-west, and divides into lesser 

 waves, one of which passes up the Channel, and another round 

 Scotland and into the North Sea, as previously mentioned, while 

 minor wave-crests flow northward into the Irish Sea and the 

 Bristol Channel. The chart thus supplies the data by means of 

 which we can calculate the approximate time of high tide for any 

 one port from that of another. 



Although the time of high water varies so greatly on the same 

 day over such a small area of country, yet that time for any one 



