§ 426, 427. THE SPECIFIC GKAVITY OF THE SEA, ETC. 207 



nace (§ 151) in the beautiful economy of Nature for tempering 

 climates there. 



426. The hydrographic basin of the Arctic Ocean is large, and 

 iiow the littoral wa- it dclivers into that sea annually a very copious 



ters, by being diluted . o 1 • i n n ^ 



from the rivei-s and clramage. bucii au immcnsc volume 01 iresh wa- 



the rains, serve as a ti ^ • n i». 



mantle for the saiter tcr aiscnargeci luto SO Small a sea as the Arctic 



and warmer sea wa- . ^ n t i • • i . 



ter below. Occau IS must go lar toward diluting its brme. 



Fig. 2, Plate X. (§ 433), shows the extent to which the brine of 

 our littoral seas is diluted by the drainage from the Atlantic slopes 

 of the United States. It will be observed by that figure that 

 suddenly after crossing the parallel of 34° K. the water begins to 

 grow cooler and lighter. The observations for these two curves 

 are a part of the celebrated series made by Captain Eodgers in the 

 U. S. ship Yincennes all the way from Behring's Straits by the 

 way of Cape Horn to New York. He cleared the inner edge of 

 the Gulf Stream in 34°, where the waters began to grow cooler 

 and lighter, and so continued to do as he approached the shore. 

 The remarkable and sudden approach of the thermal and specific 

 gravity curves after crossing 34° K. can be explained by no oth- 

 er hypothesis than this, viz. : the surface water of the sea was so 

 diluted with the fresh water from the Chesapeake, the Delaware, 

 and New York Bays, that, notwithstanding the temperature de- 

 creased as Eodgers approached the shore, yet the specific gravity 

 decreased also, because the saltness decreased by reason of the in- 

 creasing proportion of river water as he neared the shore. And 

 thus we have in our own waters an illustration and an example 

 of how cool and light — because not so salt — water may be made 

 to cover and protect as with a mantle a sheet of warmer, but Salt- 

 er and heavier water below. 



427. The mean specific gravity of the Arctic Ocean water as 

 An under current of obscrvcd bv Eods^crs, and xcduccd to the freezinoj 

 heavy water. poiut (27°.2) of sca watcr, was 1.0263. The spe- 

 cific gravity of the Gulf Stream water, as observed by him, and 

 reduced to the same temperature (27°.2), was 1.0303. If these be 

 taken as fair specimens of the water of the torrid and frigid zones, 

 it would appear that the waters of intertropical seas have 15 per 

 cent, more salt in them than the surface water of the Arctic Ocean 

 has. It is to be regretted that the hydrometer has not been more 

 frequently used in the Arctic Ocean, for a careful series of obser- 



