WAVE OF HIGH WATER. 325 



England and Ireland. Attention has already been di- 

 rected to the fact that the wave of open Atlantic coasts 

 moves with great velocity, as compared with those of the 

 inner coast-lines of Europe. 



The wave which proceeds from Ushant at 3^ 52"^ along 

 the west of Ireland reaches Hammerfest, near the North 

 Cape, at 1 1^ 35"^, whilst the derivative wave, which passes 

 from Ushant up the Channel, only reaches Calais at 1 1^ 42"^, 

 7 minutes later than the arrival of the kindred wave at the 

 extreme north-west of Europe. This retardation in velocity 

 is accompanied by a great increase in the magnitude of the 

 wave ; for whereas on the west coast of France the average 

 height of spring tides is under 16 feet, at Granville and Can- 

 cale, on the coast of Normandy, the tides rise to 37 feet. 

 A wave of this magnitude will obviously dominate the wave 

 of the south coast of England ; and hence it results that 

 from the Land's End to near Christchurch the normal 

 wave altogether disappears, and is replaced by an abnormal 

 wave, 16 feet in height, at the Land's End, which merges 

 into the normal wave near Christchurch (opposite Granville 

 and Cancale), at which place it has already dwindled down 

 to 5 feet in height. 



In like manner the normal wave of the south of Ireland 

 altogether disappears, partly from the action of the wave of 

 the adjacent coast of England, which passes up the Irish 

 Channel with like retarded velocity and increasing magni- 

 tude, and partly also from the combined action of the 

 adjacent continents of Europe, Asia, and Africa. Hence 

 an abnormal wave moves aloi^g the south coast of Ireland 

 with a maximum height of about 13 feet, but gradually 

 dwindling down until at Courtown Bay it is absolutely ex- 

 tinguished, whence northward, as from Christchurch east- 

 ward, high water is nearly simultaneous over a consider- 

 able extent of coast. 



The small condensed group of the Eaeroe Isles, situate in 



