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HYDROGRAPHY. 



[Sect III. 



coal can be generally relied upon as at hand ; nature and 

 quality of the material ? &c. 



Are there any piers, jetties^ or wharfs for landing pas- 

 sengers, or cranes for carriages, and at what time of tide 

 available ? If the country be low, are there any sea walls 

 and would the country be flooded by their removal ? 



Waves. 



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6. Lastly, the attention of tlie observer should be 

 directed to the measurement of the height, the extent 

 and the velocity of the waves of the ocean. Not only of 

 those high swelling seas which are common to every gale, 

 but especially of those gigantic ridges which are occa- 



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and even in the Atlantic ; coming in couplets and triplets 

 in the course of a gale, and occasioning fearful lurches 

 which are long remembered. Opinions differ greatly as 

 to the dimensions of these stupendous bodies, and any 

 observations which will assist in determining their limits 

 cannot fail to be acceptable. The inquiry is, fast, as to 

 the height of the solid wave above the mean water level. 



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rate at which the wave travels, and whether the height 

 and distance of the ridges vary with the velocity. 

 Fourthly, what is the greatest estimated extent of any 

 one of those ridges. 



The most simple way of measuring the height, is, when 

 the vessel is in the lowest part of the trough between two 

 following seas, to ascend the rigging to such a height as 

 will bring the top of the wave on with the horizon, to put 

 a mark, note the inclination of the vessel, and at leisure 



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