52 THE OCEAN. 



traced these lines, the wind was low and the motion of the water very- 

 moderate. 



Prow. 



Fig. 18.— Rollings of a ship upon the waves. 



The height of the waves is not the same in all seas ; it is greater 

 when the basin is deeper in proportion to the exposure of its surface 

 to the wind, and also in proportion as the water, being less salt and 

 so lighter, yields more readily to the atmospheric currents. Thus 

 assuming equality of surface, the water of Lake Superior would be 

 raised in higher waves than that of a gulf of the sea barred on the 

 open side by islands and sand-banks. When of equal saltness, the. 

 narrowest basins ought to present the shortest and least elevated 

 waves. The waves of the Caspian Sea are not to be compared with 

 those of the Mediterranean, which again are greatly exceeded in 

 height by those of the North Atlantic ; and these latter in their turn 

 are surpassed by those of the Antarctic Sea, which spreads over an 

 entire hemisphere. 



According to Admiral Smyth, who was well acquainted with the 

 Mediterranean, the tempest waves rise from 13 to 18 feet in vertical 

 height above the trough of the sea. He has even seen quite ex- 

 ceptional waves rise to the height of above 30 feet, but the average 

 waves raised by high winds were only from about 10 to 13 feet.* 

 In one passage from Liverpool to Boston, which the celebrated 



* Cialdi, Sul moto ondoso del mare, p. 142. 



