356 



PHYSICAL GEOGRAPHY. 



\<3> 



and Great Southern Oceans, is analogous to that of the upper to the lower belt ; and upon 

 the tide-waves of the Pacific reaching the mouth of the Atlantic, they move along its 

 basin, with some local exceptions, in the line of its direction, from south to north, across 

 from the African to the American coast. In the deep and open ocean, the undulation 

 travels with immense velocity, amounting to nearly 1000 miles an hour. 

 The tide-waves of the Atlantic thus advancing northwards cause the time of high 



water to be successively later at 

 the different ports on the west 

 coasts of Africa and Europe, 

 and the east coast of North and 

 South America, except from Rio 

 Janeiro to the Falkland Islands, 

 where the advance of the wave- 

 summits is from east to west. 

 The tide-wave, which is at 

 the Cape of Good Hope at a 

 certain hour, is at the British 

 Isles about fifteen hours after 

 wards, where, interrupted in its 

 progress, it divides into three 

 branches : one branch flows 

 eastward up the English Chan 

 nel, passing through the Straits 

 of Dover, and is off the mouth 

 of the Thames at the Nore in 

 about eight hours from the time 

 it entered the Channel ; a se 

 cond branch advances through 

 St. George's Channel into the 

 Irish Sea ; while the third and principal branch of the same wave proceeds along the 

 west coasts of Ireland and Scotland, rounds the northern extremity of the latter, flows 

 slowly down the North Sea, and meets the first branch at the mouth of the Thames, 

 having taken about twenty hours to compass the distance. The annexed sketch repre 

 sents the course of the latter around Great Britain. Supposing the moon to have passed 

 the meridian of Brest, at the north-western extremity of the French coast, at twelve 

 o'clock in the day, it is high water there soon after three o'clock in the afternoon, the 

 ridge of the tide-wave stretching out into the Atlantic in a north-west direction from 

 Ushant, falling a little to the south of Cape Clear, in Ireland. By six o'clock the wave 

 has gained the north coast of Ireland, the ridge maintaining the same direction ; and 

 three hours afterwards it has reached the Orkneys, the ridge bearing due north. By 

 twelve o'clock the wave has entered the German Ocean, the ridge-line extending eastward 

 from the Scottish coast to the south point of Norway : and in about eleven hours after 

 wards it has flowed down the eastern extent of England to the entrance of the Thames. 



It has been observed, that while in open seas, as around the islands of the Pacific, and 

 St. Helena in the South Atlantic, the tides have only an elevation of one or two feet, 

 in many narrow channels, like the English and St. George's, they rise to a far greater 

 height, owing to the confined space into which the water is crowded. The Bristol 

 Channel opens widely to the south-west, where it receives the tide-wave of the Atlantic, 

 but it is very contracted at its upper end, and the water is heaped up in consequence, 

 much above the level to which it otherwise would rise, attaining to an elevation of forty 



FRANCE 



