Chapter 4 

 SEAS AND SWELLS 



The characteristics of storm waves that most impress the observer 

 are their irregularity and steepness, also their great heights in many 

 cases, and the frequency with which their crests break, all of which 

 may be summed up in the term "fierceness" (figs. 18 and 19) . As long 

 as waves are still in this stage of development, the combined pheno- 

 menon is known as a "sea" ; one speaks of a "high sea," of a "low sea," 

 of a "rough sea," of a "smooth sea," as the case may be. But the 

 shapes of the waves undergo wide alterations when the wind dies 

 down, or when the waves produced by a given wind system advance to 

 regions outside the latter, as very commonly happens. The wave train 

 in question is then known as a "swell," and the individual waves as in- 

 dividual "swells." The outstanding characteristics of a swell, as 

 contrasted with a sea, are its low, rounded crests, the comparative 

 smoothness of its surface contours, its great length from crest to 

 crest, and the broad sidewise expanse of its individual crests; its 

 gentleness, in a word, contrasted with the fierceness of the waves that 

 composed the storm sea from which it has developed. 



There is nothing astonishing to the observer in the fact that rough 

 seas are the usual accompaniment of stormy weather, for the power 

 of the wind forces itself on the attention of anyone who has to walk 

 against it. But the succession of low ridges, separated one from the 

 next by distances that may be as long as 800 to 1,000 feet, or even 

 longer, that disturb the glassy surfaces of the open sea on a calm day 

 is a phenomenon that must almost be seen to be believed, because the 

 observer neither sees nor feels any immediate cause for their existence. 



ALTERATION OF SEAS INTO SWELLS 



The reason that a sea alters into a swell when the wind dies is 

 that the waves then begin to loose energy, the shorter ones with the 

 least energy becoming lower and disappearing first, so that the longer 

 ones alone are left. At the same time, the sharp peaks so frequent 

 during a rough sea subside; the irregularities of the surface tend to 

 smooth out ; any cross seas that may have been running upon the pri- 

 mary wave pattern either die down also, or are absorbed by the latter ; 

 and the remaining crests decrease progressively in height and become 

 more rounded. The end result is that the waves tend to approach the 



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