28 PHYSICAL GEOGRAPHY OF THE SEA. 



Thus Captain Wilkes, commander of the IT. S. Exploring: 

 Expedition, found the height of the waves near Orange Har- 

 bour, where they rose higher and more regular than at any 

 other time during the cruise, to be thirty-two feet (depression 

 and altitude), and their apparent progressive motion about 

 twenty-six and a half miles in an hour. 



Sir James Eoss calculated the height of the waves on a strongly 

 agitated sea at twenty-two feet, and, according to the French 

 naturalists who sailed in the frigate " La Venus," on her voyage 

 round the world, the highest waves they met with never exceedeil- 

 that measure. 



Thus, according to the joint testimony of the most eminent 

 nautical authorities, the waves in the open sea never attain the 

 mountain-height ascribed to them by the exuberant fancy of 

 poets or exaggerating travellers. But when the tempest surge 

 beats against steep crags or rocky coasts it rises to a much 

 more considerable height. The lighthouse of Bell Eock, though 

 112 feet high, is literally buried in foam and spray to the very 

 top during ground-swells, even when there is no wind. On the 

 20th November, 1827, the spray rose to the height of 117 feet 

 above the foundation or low-water mark, which, deducting 

 eleven feet for the tide that day, leaves 106 feet for the height 

 of the wave. The strength of that remarkable edifice may be 

 estimated from the fact, that the power of such a giant billow 

 ia equivalent to a pressure of three tons per square foot. 



In the Shetland Islands, which are continually exposed to the 

 full fury of the Atlantic surge (for no land intervenes between 

 their western shores and America), every year witnesses the 

 removal of huge blocks of stone from their native beds by the 

 terrific action of the waves. "In the winter of 1802," says 

 Dr. Hibbert, in his description of that northern archipelago, " ti 

 tabular-shaped mass, eight feet two inches by seven feet, watj 

 dislodged from its bed and removed to a distance of from 

 eighty to ninety feet. I measured the recent bed from which a 

 block had been carried away the preceding winter (a.d. 1818), 

 and found it to be seventeen feet and a half by seven feet, aDd 

 the depth two feet eight inches. The removed mass had been 

 borne to a distance of thirty feet, when it was shivered into 

 thirteen or more lesser fragments, some of which were carried 



