determined theoretically from a consideration of the wind energy 

 available for v;ave foriaatlon if tie fundamental assumption is 

 made that the velocity (period) of a wave always increases with 

 time . 



The area in which waves are formed is called the generating 

 area . In such an area waves receive energy from the wind by two 

 processes, by the push of the wind against the wave crests and 

 by the ^oull or drag of the wind on the water. 



The energy transfer by push depends upon the difference 

 between wind velocity and wave velocity. If the waves advance 

 v/ith a speed much less than that of the wind the push is great , 

 but if the two velocities are equal no energy is transferred. 

 If the waves travel faster than the wind they receive no energy 

 by push but on the contrary they meet an air resistance comparable 

 to the air resistance against a traveling automobile. The effect 

 of the push of the wind or of the air resistance against the wave 

 depends on the wave form. There enters, therefore, a fundamental 

 coefficient which is related to the degree to -vhich the wave is 

 streamlined and viiich is called the "sheltering coefficient." The 

 determination of this coefficient is necessary for an exact evalua- 

 tion of energj^ transfer by push. 



The pulling force of the wind alw^ays acts in the direction of 

 the wind. lb is the same at the wave crest and the wave trough 

 but the effect differs. Energy is transferred from the air to the 

 water (the movement of the surface layer is speeded up) if the sur- 

 face water moves in the direction of the wind, but energy is given 



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