the area in ■which it was generated hy wind action o This is the wave 

 which we generally call .svirello Its nature is explained by the fact tiiat 

 the water particles on the^ surface turn in circles 5 the dia-meter of 

 which is equal to the height of the wave h (see Figure l)o The water 

 particles return to their original position and it is only tte shape 

 of the wave that moves forward ^ not the water particles o The profile 

 of the wave is described by a point in close connection with a circle- 

 concentric with one of the circles shown but greater than these— as 

 the circle rolls on a horizontal line at a speedy v, aqual to tlbe 

 speed of the wave. The profile is called a trochoido 



Tte length of a wave is the distance between two wave crests or 

 tvfo wave troughs; it is represented by Lo The height of the wave^ hj 

 is the distance between the crest and the trough of the wave „ The 

 length of the wave divided by the speed of travel of the wave shape 

 is called the period ^ T. 



The raoverfBnts of the wave are not confined to tte surface alone j 

 but continue downward as the diameter of the circle steadily decreases o 

 Theoretically the diameter becomes zero at a tremendous depth, but in 

 general one can say that wave motion has ceased at a certain depth 

 which is dependent upon the dimensions of the waveo In our in^gination 

 we can form a picture of the movement by thinking of an elastic strixig 

 which is fastened at this depth while the other end moves around the 

 top circle o All other points on the string will then draw circles 

 •with diameters which decrease proportionallj'- with the depths The 

 drawing (Figure 1) must be regarded as purely schematic; as a matter 

 fact, the displacenent does not decrease in a straight line with the 

 deptho 



Since the deep-water wave motion does not reach the ocean bottosL, 

 it of course cannot influence the latter; however, the wave motion is 

 an expression of the energy which has been given to the water by tbe^ 

 windo This energy can be expressed in the forrnt 



E = JrL (1 + e ~L — ) 



where z is the depth of the water at a certain point » We can see 

 that when s is large in comparison to L^, the part in the bracket 

 can be ignored and we have: 



E - h^ L 



The .speed with which the wave moves, that iSj the speed with 

 which the energy transferi-ed from the wind to the vrater moves forward^ 

 can be exoressed ass 



- 1025^' L 



