The Tides. 215 



situate 400 miles west of Ceylon, and occupj- 500 miles in a north 

 and south direction by about 40 miles wide. They are divided into 

 numerous groups by navigable channels of various depths. It is 

 estimated that the whole number of islands or Atols is no less 

 than 50,000, of which the largest is not more than eight miles in 

 circumference. These islands present an immense barrier to the 

 tide, so that one portion is retarded, while another portion moves 

 on rapidly, making a large detour returns upon the retarded 

 portion like an eddy. The wave moving westward with a great 

 convex front reaches Madagascar, and, passing around both ends, 

 fills Mozambique Channel with high water in half an hour. One 

 portion then passes southwest and meets the south Atlantic tide, 

 the other advances north to Cape Grardaf ui, then moves eastward 

 with great velocity to the west coast of Hindoostan, filling the 

 Arabian sea, and moving south reaches the Maldives eight hours 

 after the main wave has passed the same point and entered the 

 Bay of Bengal. It will also be observed that the easterly side of 

 this tide moves both north and south of Australia ; that on the 

 north meets the Pacific tide coming through Torres straits with a 

 difference of four hours ; that on the south travels beyond Tas- 

 mania and joins a portion of the Pacific tide, a portion of both, 

 however, returning from South Victoria along the Antarctic conti- 

 nent to maintain the equilibrium. 



The tide in the north Atlantic, which had its origin partly in 

 the Arctic Ocean and partly in the south Atlantic, moves eastward 

 with an extensive convex front and divides on the south end of 

 the British Isles ; one portion enters the British Channel and 

 reaches Dover Straits in the time that the other portion makes the 

 entrance to the Korth Sea. The tide in Dover Straits meets 

 another which entered the North Sea twelve hours before but 

 passes to the east of it and along the coast of France and the 

 Netherlands, and combining with a later tide from the north 

 reaches the Skaw 17 hours after passing Callais, while another 

 portion of this identical tfde travels south along the English coast. 

 It will be observed that there is always a whole wave in the North 

 Sea which is necessary to preserve the sequence. 



The tide passing north to Martha's Vineyard is met at Nan- 



