30 PHYSICAL GEOGEAPHY OF THE SEA. 



formation of small waves. Numberless oscillations unite their 

 efforts, and create visible 'elevations and depressions. Mean- 

 while, the wind is constantly setting new particles in motion ; 

 long before the first oscillations have lost their effect, countless 

 •others are perpetually arising, and thus the sum of the pro- 

 pelling powers is constantly increasing, and gradually raising 

 mountain-waves, until their growth is finally limited by the 

 counterbalancing power of the earth's attraction. 



As the strength of the waves only gradually rises, it also loses 

 itself only by degrees, and many hours after the tornado has 

 ceased to rage, mighty billows continue to remind the mariner 

 of its extinguished fury. The turmoil of waters awakened by 

 the storm propagates itself hundreds of miles beyond the space 

 where its howling voice was heard, and often, during the most 

 tranquil weather, the agitated sea proclaims the distant war of 

 the elements. 



The velocity of waves depends not only on the power of the 

 impulse, but also on the depth of the subjacent waters, as I have 

 already mentioned in the preceding chapter. 



For this reason, as increased velocity augments the power of 

 the impulse, the waves in the Atlantic or Pacific, the mean 

 depth of which may be estimated at 12,000 or 18,000 feet, 

 attain a much greater height than in the comparatively shallow 

 North Sea. 



The breaking of the waves against the shore arises from their 

 velocity diminishing with their depth. As the small flat wave 

 rolls up the beach, its front part, retarded by the friction of 

 the ground, is soon overtaken by its back, moving in swifter 

 progression, and thus arises its graceful swelling, the toppling 

 of its snow-white crest, and finally its pleasant prattle among 

 the shingles of the strand. This is one of those pictures of 

 nature which Homer describes with such inimitable truth in 

 various places of his immortal poems : he paints with admirable 

 colours the slow rising of the advancing wave, how it bends 

 forward with a graceful curve, and, crowning itself with a 

 diadem of foam, spreads like a white veil over the beach, 

 leaving sea-weeds and shells behind, as it rustles back again 

 into the sea. 



The height which waves may attain on the open sea has 



