84 Ocean Waves 



10. With regard to the origin of ocean- waves, Professor 

 Airy observes, "it is to be understood that either from 

 preceding disturbances or from trifling irregularities in the 

 action of the wind while the water is smooth, there are very 

 shallow undulations on the water. 



Now, with all due deference to so great an authority, this 

 surely attributes these stupendous and invariable results 

 primarily to an accident. For, be it observed, every wave, 

 no matter how enormous, must have had origin in a primary 

 wavelet : to say it started into being at any other stage, is 

 merely to enlarge the supposed magnitude of such first 

 wavelet. In fact, the word regularities might be justly 

 substituted for irregularities in the above remark ; for the 

 Professor's own mode of demonstration shows how the force 

 of the wind acting in the direction of a tangent to the 

 surface may produce the initial wavelet. 



Let a h (fig. 1, plate I) be the smooth surface of water, c a 

 particle of a column of air moving in the direction of the arrow ; 

 d esb stationary column of air. When the breeze commences, 

 the particle c is pressed against the particle d, which being 

 stationary, reacts the pressure in all directions, shown by 

 the dotted lines. Thus, a downward pressure is produced, 

 and also a retrogressive pressure in the resulting hollow, in 

 accordance with the theoretical motion of the particles of 

 water ; while the particle c being reinforced, the column 

 d e yields, and the onward motion of the wavelet takes 

 place. 



Regarding the wind as a constant force, it now increases 

 the result, viz., the initial wavelet, in volume and velocity. 

 But this acceleration in the magnitude of the wave has its 

 practical limit, for the wave recedes from the advancing air, 

 and the wind, although a constant, being thus also a follow- 

 ing force, its imjjulsive effect on the wave becomes retarded 

 with the increase in the magnitude, and therefore, the 

 velocity (9) of the wave ; so that, if the maximum force of 

 the wind be known, the maximum dimensions of waves 

 may be ascertained. The observed results agree in the main 

 with theory. Were it not for the cause stated, it is obvious 

 that, in a continuous gale of wind, waves would go on 

 increasing to indefinite dimensions. 



11. The force resident in a wave then is to be considered 

 not as the received strength of the wind simply, but as the 

 aggregated impulse from the time of its commencement. 

 The wave becomes in fact a storehouse of power, retaining, 



