212 THE PHYSICAL GEOGRAPHY OF THE SEA. 



■field of ice averaged a thickness of not less than seven feet ; 

 at least that was the case with De Haven. A field of ice ccfvering 

 to the depth of seven feet an area of 800,000 square miles, would 

 weigh not less than 18,000,000,000 tons. This, then, is the quan- 

 tity of solid matter that is drifted out of the polar seas through 

 one opening — Davis' Straits — alone, and during a part of the year 

 only. The quantity of water which was required to float and 

 drive this solid matter out was probably many times greater than 

 this. A quantity of water equal in weight to these two masses 

 liad to go in. The basin to receive these inflowing waters, i. e., 

 the unexplored basin about the North Pole, includes an area of 

 a million and a half square miles ; and, as the outflowing ice and 

 water are at the surface, the return current must be submarine. 

 A part of the water that it bears probably flows in beneath Dr. 

 Kane's barrier of ice (§ 429). 



432. These two currents, therefore, it may be perceived, keep 

 Volume of water kept ^^ Hiotiou bctwecn the tcmpcratc and polar regions 

 iTCtiJ'^flow and ?e- ^f the earth a volume of water, in comparison with 

 ^''^- which the mighty Mississippi, in its greatest floods, 

 sinks down to a mere rill. On the borders of this ice-bound sea 

 Dr. Kane found subsistence for his party — another proof of the 

 high temperature and comparative mildness of its climate. 



433. The Brussels Conference recommended the systematic use 

 The hydrometer at ^^ ^^ hydrometer at sea. Captain Eodgers, Lieu- 

 ^*^- tenant Porter, and Dr. Euschenberger, all of the 

 United States Navy, with Dr. Raymond, in the American steamer 

 Golden Age, and Captain Toynbee, of the English East Indiaman 

 the Gloriana, have all returned to me valuable observations with 

 this instrument. Eodgers, however, has aflbrded the most ex- 

 tended series. It embraces 128° of latitude, extending from 71° in 

 one hemisphere to 57° in the other. And here I beg to remark, 

 that those navigators who use the hydrometer systematically and 

 carefully at sea are quietly enlarging for us the bounds of knowl- 

 edge and our field of research. These observations have already 

 led to the discovery of new and beneficent relations in the work- 

 shops of the sea. In the physical machinery of the universe 

 there is no compensation to be found that is more exquisite or 

 beautiful than that which, by means of this little instrument, has 

 been discovered in the sea between its salts, the air, and the sun. 



