THE SEA AND THE ATMOSPHERE. 



6. Its lieighL— At the lieiglit of 26,000 miles from tlio earth, 

 the centrifugal force avouIcI counteract gravity ; consequently, all 

 ponderable matter that the earth carries with it in its diurnal 

 revolution must be within that distance, and consequently the 

 atmosphere cannot extend beyond that. This limit, however, 

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

 balloon 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 sound cannot travel through vacuum, it was 

 inferred that the explosion took place within the limits of the 

 atmosphere. Herschel concludes that the aerial ocean is at 

 least 50 miles deep. 



7. Data conjectural. — The data from which we deduce our 

 estimate, both as to the mean height of the atmosphere and 

 average depth of the ocean, are, to some extent, conjectural ; 

 consequently, the estimates themselves must be regarded as 

 approximations, but sufficiently close, nevertheless, for the 

 present pui-poses of this work. 



8. Analysis of azV.— Chemists who have made the analysis, tell 

 us that, out of 100 parts of atmospheric air, 99.5 consist of oxygen 

 and nitrogen, mixed in the proportion of 21 of ox^-gen to 79 of 

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

 Tialfofa imrt consists of .05 of carbonic acid and .45 of aqueous 

 vapour. 



9. Information respecting tlie depth of tie ocean.~The average 

 depth of the ocean has been variously computed by astronomers, 

 from such arguments as the science affords, to be from 2G 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.j 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 



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



t ['And le it further enacted. That the Secretary of the Navy be directed to 

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

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

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

 operate m procurmg materials for such investigations, in so far as said oo-opera- 

 tion may not be incompatible with the pubUc interest3."-rrom Naval Ap- 

 propriation Bin, approved March 3, 1849. 



B 2 



