THE SPECIFIC GRAVITY OF TilE SEA, ETC. 207 



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 smface, the 

 return current must be submarme. A part of the water that it 

 bears probably flows in beneath Dr. Kane's barrier of ice (§ 429). 



432. These two cm-rents therefore, it may be perceived, keep in 

 Volume of water motiou between the temperate and polar regions of 

 SaJSowaifd ^^^6 ^^^^^^ a volume of water, in comparison with 

 reflow. 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 of the 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 each returned to me valuable observations with 

 this instrument. Eodgers, however, has afforded 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 re- 

 mark, that those navigators Vfho use the hydrometer systematically 

 and carefully at sea are quietly enlarging for us the bounds of 

 knowledge ; and they are gleaning in our field of research. These 

 observations have already led to the discovery of new and beneficent 

 relations in the workshops 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 httle 

 instrument, has been discovered in the sea between its salts, the 

 air, and the sun. The observations made with it by Captain 

 EodgerSjOn board the U. S. ship " Yincennes," have shown that the 

 specific gravity of sea water varies but httle in the trade-wind 

 regions, notwithstanding the change of temperature. The tempe- 

 ratm-e was a little greater in the south-east trade-wind region of the 

 Pacific ; less in the Atlantic. But, though the sea at the equa- 

 torial borders of the trade-wind belt is some 20° or 25° warmer 

 than it is on the polar edge, yet the specific gravity of its waters 

 at the two places in the Atlantic difters but little. Though the 

 temperature of the water was noted, his observations on its specific 

 gravity have not been corrected for temperature. The object which 

 the Brussels Conference had in view when the specific gravity 



