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GEOGRAPHY, HYDROGRAPHY, &c. 



DESCRIPTION of the Earth. Delineation of the 

 watery portion of the terraqueous globe. 



The Ocean, its Depth, and Temperature. 



The ocean, with all its islands, bays, and seas, 

 covers an area of 145,600,000 English square miles, 

 or nearly Jths of the surface of the globe. 



Laplace has calculated that its mean depth is but 

 a small fraction of the difference of the axes of the 

 earth, which difference is 25 miles. If, therefore, 

 we suppose the mean depth to be two miles,* the 

 cubic contents will be 290,000,000 of cubic miles. 



In A.D. 1819, in lat. 4 N. at the point where 

 the approximation of the two continents of Africa 

 and America is nearest, Sir Thomas Hardy, in the 

 Superb, sent down 2000 fathoms of whale-line, with 

 six cwt. attached. At first it ran out with great ra- 

 pidity, but afterwards sluggishly. After the rope 

 that had sunk with its own weight was drawn 

 in, about 1500 fathoms appeared to be down per- 

 pendicularly, when the line, owing to the prodigious 

 strain on it, broke, and it remains uncertain whether 

 the weight attached had reached the bottom or not.f 



* This seems too high an average for the depth of the whole 

 ocean. Dr. Keill computes the surface of the whole ocean to be 

 8,549,050 square miles, with an average depth of a quarter of a 

 mile ; and even this is probably too high an estimate. 



t Ten, or at most twelve, fathoms is the very lowest a diving- 

 bell dare venture to go, the density, and more especially the heat 

 of the air, although renewed by the forcing-pumps, become so in- 

 supportable. 



