CHAPTER I. 



WIND. 



Wind the generator of sea- waves Working season Wind diagrams Direction and 

 velocity of wind Cyclones Anti-cyclones Extent of storm areas Progress 

 of storms Wind-gauges Relation of wind velocity to pressure Relative 

 frequency of gales on the British coasts Forecasting gales Monsoons 

 Significance of clouds, etc. Lunar rainbows Halos Rollers arriving before 

 gale Harbour entrances and direction of littoral drift affected by wind 

 Arresting wind-blown sand. 



SINCE wind is the generator of ordinary sea-waves, almost all 

 the troubles which beset the construction of sea-works are 

 attributable to it. 



It is not possible to foretell the advent of heavy seas, except 

 by forecasting the wind which produces them ; l those in charge 

 of sea-works will therefore do well to anticipate gales, to the 

 best of their ability, and by taking such precautionary measures 

 as may be deemed necessary, or as may be within their power to 

 adopt, prepare in time for the heavy seas which they know the 

 wind will bring up. Work should also be arranged so as to 

 take advantage of what is usually termed the " working season," 

 being that part of the year during which gales are least frequent 

 and the sea smoothest. 



This period will be found to vary much on different coasts, 

 according to the extent and direction of their exposure ; and in 

 different parts of the world, according to the season of the year. 



The direction of littoral drift is, in the great majority of 

 cases, determined almost solely by that of the prevailing winds ; 

 and there are other considerations, to which reference will be 

 made in the sequel, which render a knowledge of the general 

 direction, strength, duration, relative frequency and sequence of 

 the winds prevailing in any locality where the construction of 

 sea- works is contemplated, very necessary. 



1 In regard to swell sometimes preceding storms, see pp. 19, 20. 



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