CHAPTER XVIII 



THE FORMS CARVED AND MOLDED BY WAVES 



The motion of a water wave. The motions within a wave 

 upon the surface of a body of water may be thought of in two 

 different ways. First of all, there is the motion of each particle 

 of water within an orbit of its own ; and there is, further, the for- 

 ward motion of propagation of the wave considered as a whole. 



The water particle in a wave has a continued motion round and 

 round its orbit like that of a horse circling a race course, only that 

 here the track is in a 

 vertical plane, directed 

 along the line of propa- 

 gation of the wave (Fig. 

 247). Each particle of 

 water, through its fric- 

 tion upon neighboring 

 particles, is able to 

 transmit its motion both 

 along the surface and 

 downward into the water 

 below. The force which 



Ware 



FIG. 247. Diagram to show the nature of the 

 motions within a free water wave. 



starts the water in mo- 

 tion and develops the 

 wave, is the friction of 

 wind blowing over the 



water surface, and the size of the orbit of the water particle at 

 any point is proportional to the wind's force and to the stretch of 

 water over which it has blown. The wind's effect is, therefore, 

 cumulative the wave is proportional to the wind's effect upon 

 all water particles in its rear, added to the local wind friction. 



The size or height of the wave is measured by the diameter of the 

 orbit of motion of the surface particle, and this is the difference 

 in height between trough and crest. The distance from crest 

 to crest, or from trough to trough, is called the wave length. 

 Though the wave motion is transmitted downward into the water, 



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