§ 7-10. THE SEA AND THE ATMOSPHERE. 3 



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 sound can not travel through vacuum, it was inferred that the 

 explosion took place within the limits of the atmosphere. Her- 

 schel concludes that the aerial ocean is at least 60 miles deep. 



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

 Data conjectural, mcau 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 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. 100 parts of atmosphcrlc air, 99.5 consist of oxygen 



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

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

 of a part consists of .05 of carbonic acid and .45 of aqueous vapor. 



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

 information respect- putcd bv astrouomcrs, from such are^uments as the 



ing the depth of the ^ . nr. ^ ^ o r> /^ -. ^ -i 



ocean. scicucc aftords, to bc irom 26 to 11 miles. About 



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

 navy a plan for "sounding out" the ocean with the plummet.f 

 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 part — yet more knowledge has been 

 gained concerning the depths and bottom of the deej) sea, than all 

 the world had before acquired in all previous time. 



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

 Its probable depth, not thus far authorize the conclusion that the aver- 

 age depth of ocean water is more than three or four miles (§ 3), 

 nor have any reliable soundings yet been made in water over five 

 miles deep. 



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



t And be it further enacted, That the Secretary of the Navy be 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 

 ef the ocean ; and to cause the vessels of the navy to co-operate in procuring materi- 

 als for such investigations, in so far as said co-operation may not be incompatible. 

 with the public interests." — From Naval Appropriation Bill, approved March 3, 1849. 



