112 Ratio of the Length and Height of Sea Waves. 



progress of a ripple only, from birth to extinction, the same 

 reasoning obviously extends to that of the heaviest sea. For, 

 be it observed, the largest sea must have had its origin in a 

 primary wavelet, as at the point A; and we have only to 

 extend the period of increase from A to B further towards 

 D, as in the annexed figure (Fig. 2), to obtain the larger 

 waves. The magnitude of the wave, in fact, is proportional 

 to the period of increase, while being increasingly urged by 

 the wind during the progress of the wave from A to B, and 

 this time must obviously be dependent upon the extent of 

 the fetch of free water over which the wind may extend ; 

 so that the strength and range of the wind being the same, 

 the magnitude is proportioned to the fetch. A storm-wave 

 therefore of forty feet in height may have the same profile 

 as a ripple, from which indeed it must have sprung, and in 

 the same way the declining ground-swell of an ocean has its 

 miniature facsimile in a pond. 



The annexed diagram (Fig. 3) may practically illustrate 

 the foregoing remarks. A represents accurately the average 

 profile of the permanent south-west swell in the Southern 

 Ocean in latitude from 40° to 48° S., arising from the pre- 

 vailing winds around the Pole. The curve is taken from 

 entries of a number of profiles drawn from observation in a 

 recent voyage of the ship " Newcastle" from Melbourne vid 

 Cape Horn to London, and the same curve and dimensions 

 are identifiable throughout in the same latitudes. B in like 

 manner represents the profile and dimensions drawn to the 

 same scale of presumably the same permanent south-west 

 ground swell as it reaches the southern coast line of Aus- 

 tralia, averaged from many sketches of such profiles taken 

 on the spot. The outline A therefore represents the swell 

 in its active or mature state at or about its maximum ratio 

 of height to length in a stage when the height and the bulk 

 of water moved oppress the mind with a sense of sublimity ; 

 and B represents it in its decline, when, after having 

 traversed forty degrees of a great circle, or more than two 

 thousand miles, it approaches dissolution. The height here 

 is comparatively nil, and the length has increased almost to 

 flatness. Yet this enormous swell had its origin in the Polar 

 sea, as an initial wavelet, the relative magnitude of which 

 could only be represented in the diagram by a dot. 



Instead, however, of tracking a wave through this vast 

 distance we may picture it as fixed and subsiding in a single 



