February 1, 1890.1 



KNOWLEDGE, 



water rolls forward on a flat shore in a new form of wave, 

 called the solitary wave, or wave of translation. Fig. .3 

 illustrates this condition of things. The characters of the 

 solitary wave will be discussed in a later article. 



One of the first problems which presents itself to the 

 watcher of waves is the circumstance that, at the opposite 

 shore of a bay, across which we will suppose him to look, 

 the waves travel in exactly the opposite sense (or direction) 

 to those which roll in to the beach on which he stands. 

 To all appearance the waves, when the air is calm, come 

 from some distant source of disturbance — say in the open 

 ocean — and there seems at first no obvious reason why the 

 waves should advance directly upon every part of the 

 shore however much the shore line may twist and turn, so 

 that at every part of the shore the line of breakers, and 

 the crests immediately following the breakers, are parallel 

 to the beach. This is due to the circumstance already 

 mentioned that the progress of a wave becomes slower as 

 the depth of the water becomes less and less. Thus, if a 

 wave crest enter a bay or inlet, the middle part, which is 

 in deep water, will retain its velocity, whilst to right and 

 left the wave is retarded. Where the drag of the sea- 

 bottom is felt the wave hangs back, and the crest swings 

 round each cape or promontory, as a line of soldiers wheels 



former winds, or from a distant storm, two sets of breakers 

 may sometimes be perceived, the larger rolling in directly 

 upon the shore, and the smaller (small both in height and 

 in length and moving slowly) coming in at an angle, and 

 breaking first at the windward end. More often than not 

 the smaller, slanting wave is caught up and smothered 

 by the larger and quicker waves, so that it is only occa- 

 sionally, at opportune moments, that the little side waves 

 are able to discharge themselves upon the beach. There is 

 another point to be noticed when a side wind sends smaller 

 undulations athwart the larger waves. These smaller 

 undulations may b'e observed to indent, or serrate, the 

 crests of the larger waves, carving them into ridge and 

 furrow. If the eye be turned to the roller immediately 

 behind the breaker it will often be noticed that the crest is 

 not a straight line, but has an undulating form. Now let the 

 eye follow this roller as it nears the shore, and becomes in 

 its turn the breaking wave. The crest is higher in some 

 places than in others ; the water there is deeper, and these 

 parts of the crest, therefore, move faster than the lower 

 parts. They consequently break first ; and by rapidly 

 running the eye along the crest of the breaking wave 

 one may see that there are a number of portions oi 

 the wave of about equal length where the crest is break- 



Fio. 2. — The Alternation of Rough aud Smooth Water. 



on parade, when the inside man marks time and the 

 outside man marches at the regulation rate. Thus the 

 wave crest wheels and advances towards the beach, its 

 whole length being nearly parallel to the shore at the time 

 the crest begins to break. Those parts of the crest which 

 are a little further from the beach are travelling faster, and 

 quickly come alongside the breaking portion of the crest. 

 At the edge of the shore every circumstance combines to 

 give the impression that the waves for a considerable 

 distance out to sea are advancing directly upon the beach. 

 From the top of a moderate cliff it is, however, easy to see 

 that this is to some extent an illusion. In a side wind, 

 especially, it is only close in shore that the wave crests 

 range themselves in long ridges approximately parallel to 

 the beach. 



When the wind sets in at an angle with the shore line, 

 and the waves are no longer free but forced, the windward 

 end of the breaker breaks first, and the curling cusp runs 

 to leeward along the crest as the wave swings round, each 

 portion of the crest successively discharging itself upon the 

 beach when it reaches about the same distance from tlie 

 shore line as that at which the windward end of the wave 

 first broke. The line to which the surf reaches is conse- 

 quently very nearly parallel to the shore line. When a 

 light side wind springs up across a sea still agitated from 



iug, and that these breaking portions are separated by 

 unbroken portions which are the troughs of the sideways 

 undulation. 



When large waves are rolling iu to shore on a calm 

 day after a storm, one may sometimes see breakers with 

 straight, unfuiTowed crest, which come in direct and dis- 

 charge themselves simultaneously along their whole length 

 with thundering sound. On a flat shore the finest breakers 

 are these given by the ground swell, especially in a light 

 oft'-shore wind, when the great wave slides smoothly on to 

 the very margin of the water and discharges itself right 

 upon the beach. 



The simple heave oi the ground swell is, however, an 

 exceptional condition of the sea. Generally the surface is 

 covered with undulations of various size, moving inde- 

 pendently in difierent directions, which the watcher of 

 waves cannot too early accustom himself to detect. One of 

 the most familiar beauties of the sea, the laughter of the 

 sunlit waves, is due to these complex motions. The 

 dancing, sparkling points of light are one of the great 

 charms of a shore which faces the sun. When the early 

 riser sees the sunlight sparkling on the summer sea, and 

 goes out into the freshness of the new day, he knows, as 

 few others know, the true joy of the morning. When 

 the sun first appears above the sea a narrow lane of 



