THE FORMATION OF SEA-WAVES. 493 



in fact, if we carefully examine a wave, we shall find that it is covered 

 with very fine ripples, that correspond to the atmosj)heric vibrations. 

 The ripples give rise to wavelets, which correspond to the undulations 

 of the air, and are seen on the upper part of the waves. The wave 

 proper appears to consist of a series of wavelets. A number of waves 

 constitute a billow ; a series of billows gives rise to a heavy sea (/>- 

 quet de mer) ; a series of heavy seas produces the great swell or tidal 

 wave of the storm. 



From the nautical point of view, the ripples are of no importance, 

 for they are seldom more than a few millimetres in diameter ; but 

 from the scientific point of view they may be considered as the-origin 

 of the swing of the liquid element, for they engender the wavelets. 

 The last are still of no interest to the sailor, but are important in their 

 relation to works of art, which are disintegrated by their blows, ap- 

 parently insignificant, but infinitely multiplied. The wavelets are 

 from ten to thirty centimetres in diameter and not very long. A very 

 heavy wind breaks them up and contributes to the formation of a fine 

 dust of salt water or salt spray, which is destructive to vegetation on 

 exposed coasts. The wave proper may, in the English Channel, be 

 about ten feet high, thirty feet or more broad, and eighty feet long ; 

 its proportions do not disturb large ships, but it is destructive, in 

 the long run, to port works, and is dangerous to small craft when it 

 breaks. We may estimate that ten waves make a billow. The first 

 of the ten may be relatively small, but the others go on increasing to 

 the last. 



The heavy seas are the terror of sailors. They represent an enor- 

 mous volume of water in motion. A gust of wind can not possibly 

 raise up such a mass, and it can only be the result of the combined 

 efforts of the tempest. A heavy sea may reach a height equal to 

 twenty-five or thirty or more feet. It is massive, and strikes like 

 a battering-ram. On the land it causes great damage, and makes 

 breaches in works of earth and stone ; at sea, it can send a trans- 

 atlantic packet to the bottom with a single blow. 



The great tidal wave is produced by two causes. On one side, it 

 is the general resultant of the billows and the great seas; and, on the 

 other hand, it is produced by barometrical depressions causing the 

 waters of the ocean to rise. In cyclones, the rise of the water in the 

 center would be neutralized by the centrifugal force, and it is there- 

 fore probable that the former cause acts alone. The tidal wave has 

 but small amplitude, but, when inclosed by parallel coasts, it may 

 rise to a height of several metres. It then causes inundations of low 

 shores. 



The singular fact has been remarked at Havre that in a storm the 

 swell almost always comes after the tide. The sea rises to its normal 

 high-water mark at the prescribed hour, and then begins to retire as 

 usual ; all at once it rises again, to a height generally much greater 



