146 



KNOWLEDGE. 



[July, 1901. 



that the latest of tlie table velocities (that given by 

 Captain Wilson-Barker) may l>i' advantageously substi- 

 tuted for the earlier ones. 



Taking 28 feet as the average height of the waves 

 in a violent storm in the ocean, and assuming that the 

 average length is then 20 times the average height whiih 



the more 

 in height 

 limited bv 



we know to be approximately the case, the wave length 

 would be 560 feet, and, the speed of the wave, therefore. 

 33 feet per second, 36 statute miles per hour. The wind 

 will then be blowing some 60 miles per horn- relatively 

 to an obsen'er stationary upon the water, but only 24 

 miles an hour relatively to the waves. Waves of gi-eater 

 speed in the same storm would be subjected to a lighter 

 wind, and a wave travelling 60 miles an hour would be 

 in still air. It is not difficult to see, therefore, that the 

 most conspicuous waves in the storm, even m phine mer. 

 will not be the very longest which the wind may be 

 supposed capable of directly creating. The growth 

 in height of the longer waves is thus limited by the 

 diminution of the power of the w'ind to press upon 

 swiftly retreating form. The growth 

 of shorter waves, on the contrai-y, is 

 the circumstance that the slowly moving 

 ridge of water, being subject to almost the full force of 

 the gale, gives way if it become high and steep, bursting 

 in a shower of spindrift. 



If we look at the waves raised by the wind iipon a 

 pond we see that, commencing with wavelets about an 

 inch long close to the windward shore, there is an increase 

 in height and wave length as we recede therefrom. The 

 waves at any point on the pond soon attain the maxi- 

 mum dimensions compatible with their distance from the 

 windward shore, and however long the wind may blow 

 no further increase in their size takes place. The same 

 phenomenon can be well seen on a lake or any such 

 body of water not subjected to the distiu-bing effect of 

 a swell. 



The following Tabic (TX.) shows the relation between 



o 5^ t^ CI -.T' c; ^1 w W3 t^ ^* 1^ t^ r: i^T c-i N »p c: o . c-j —» 



ccrcibw-^-rroihtbibowsr^dooociciciffiO lib do 



i-*: M "5 



ip X LO c; t* ^ ira *-•: ~ c o ^ i.-: ri -? IN M o o w O o cc 



-*« 



; "t; C - ^ ~ 



= o 



:: — H a- o 

 ^ =;; = = S E=. 



— CO'Cp__. J:^ gi,__ I. 



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