CHAPTER V 



THE MOVING WATERS 



^LL disturbances of the world's waters, whether 

 /-\ caused by a stone tossed into a pond, by the prow 

 jL JLof an ocean hner, or by a mighty seismic upheaval 

 of the sea bed, are subject to uniform laws. Ripples, 

 waves, rollers, tides, bores and tidal waves are classifica- 

 tions of sea and river movements which help us to under- 

 stand them better, but they are all governed by the same 

 inflexible principles. 



The world's winds are the primary causes of surface 

 disturbances of the oceans, rivers and streams, and they 

 constantly build up minor movements into larger ones. 

 But although one would expect that the slightest breath 

 of air would ruffle a water surface with very small waves, 

 this does not happen : there is a limit to what the wind 

 can do. A breeze moving at two knots (12,160 feet an 

 hour) or under cannot raise even the tiniest waves on 

 any water surface. But when it is moving at just over two 

 knots it produces the very smallest waves that can exist 

 on the sea. These minimum wavelets always have the 

 same wave-length — three inches from the crest of one 

 wavelet to the crest of the next — they cannot measure 

 less. Nor can they travel at a slower speed than fourteen 

 inches a second. But from that basic size and basic speed 

 they can be built up by the wind, which does not merely 

 push them but also pulls at them, so that ripples can 

 become formidable waves, which can again be merged 

 into larger movements — breakers, tidal waves and so 

 on. 



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