THE SEA AXD THE ATMOSPHERE. 6 



revolution must be within that distance, and consequently tlie at- 

 mospliere cannot extend beyond that. This limit, however, has 

 been greatly reduced, for Sir John Herschel has shown, by bal- 

 loon observations,* that at the height of 80 or 90 miles there is a 

 vacuum far more complete than any which we can produce by any 

 air-pump. In 1783 a large meteor, computed to be half a mile 

 in diameter and fifty miles from the earth, was heard to explode. 

 As somid cannot tra^^el through vacuum, it was inferred that the 

 explosion took place vdthin the limits of the atmosphere. Herschel 

 concludes that the aerial ocean is at least 50 miles deep. 



7. The data from which we deduce om- estimate, both as to the 

 Data conjectural, mean height of the atmosphere and average depth 



of the ocean are, to some extent, conjectm^al ; consequently the 

 estimates themselves must be regarded as approximations, but suf- 

 ficiently close, nevertheless, for the present purposes of this work. 



8. Chemists who have made the analysis, tell us that, out of 

 Analysis of air. IQO parts of atmospheiic air, 99.5 consist of oxygen 



and nitrogen, mixed in the proportion of 21 of oxygen to 79 of 

 nitrogen by voliune, and of 23 to 77 by weight. The remaining 

 half of a jjctvt consists of .05 of carbonic acid and .45 of aqueous 

 vapour. 



9. The average depth of the ocean has been variously com- 

 infyrmation respect- pntcd by astrouomers, from such arguments as the 

 ocean.^ ep o e g^-^^^^g afFords, to be from 26 to 11 miles. About 

 ten years ago I was permitted to organize and set on foot in the 

 American navy a plan for " sounding out " the ocean with the 

 plummet.! Other navies, especially the English, have done not a 

 little in furtherance of that object. Suffice it to say that, within 

 this brief period, though the undertaking has been by no means 

 completed — no, not even to the tenth j^art — yet more knowledge 

 has been gained concerning the depths and bottom of the deei^ sea, 

 than all the world had before acquired in all previous time. 



10. The system of deep-sea somidings thus inaugurated does 

 Its probable depth, uot thus far authoHze tho conclusion that the average 



* Those of !Mr. Welsh, in his ascent from Kew. 



t '■'■ And he it furtlier enacted, T\\Q.t i\\Q Secretary of the Navy he directed to 

 detail three suitable vessels of the navy in testing new routes and perfecting 

 the discoveries made by Lieut. Maury in the course of his investigations of the 

 winds and currents of the ocean ; and to cause the vessels of the navy to co- 

 operate in procuring materials for such investigations, in so far as said co-opera- 

 tion may not be incompatible with the public interests."— From Naval Ap- 

 propriation Bill, approved March 3, 1849. 



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