228 PHYSICAL GEOGRArUY OF TUE SEA, AND ITS METEOROLOGY. 



the south, Avhich, by virtue of its saltness (see Fig. 2), is heavier 

 than the cool aud upper current which runs out of the polar basin, 

 and which is known as an ice-bearing current. It is the same 

 which is felt by mariners as far down as the Grand Banks of 

 Newfoundland, and recognized by philosophers off the coast of 

 Florida. This upper current, though colder than its fellow below, 

 is lighter, because it is not so salt. Figure 2 reveals to us a 

 portion of sea between the parallels of 34° and 40° north, exactl}'- 

 in such a physical category as that in which this theory presents 

 the Arctic Ocean. Here, along our own shores, the thermal curve 

 loses 12° of heat ; and what does the specific gravity curve gain 

 in the same interval ? Instead of increasing up to 1.027, accord- 

 ing to the thermal law, it decreases to 1.023 for the want of salt 

 to sustain it. Now recollect that the great American chain of 

 fresh-water lakes never freezes over. Why?_ Because of their 

 depth and their vertical circulation. The depths below are con- 

 tinually sending water above 32° to the surface, which, before it 

 can be cooled down to the freezing-point, sinks again. Now 

 compare the shallow soundings in these lakes with the great depths 

 of the Arctic Ocean ; compute the vast extent of the hydrographic 

 basin which holds this polar sea ; gauge the rivers that discharge 

 themselves into it ; measure the rain, and hail, and snow that the 

 clouds pour down upon it ; and then contrast its area, and the fresh- 

 water drainage into it, with the like of Long Island Sound, 

 Delaware Bay, and the Chesapeake ; consider also the volume of 

 diluted sea water between our shore-line and the Gulf Stream ; 

 strike the balance, and then see if the arctic supply of fresh water 

 be not enough to reduce its salts as much as our o-vnti fresh-water 

 streams are diluting the brine of the sea under our own eyes. 

 The very Gulf Stream water, which the observing vessel left as 

 she crossed 34° and entered into those light littoral waters, was 

 bound northward. Suppose it to have flowed on as a surface 

 current until it, with its salts, was reduced to the temperature of 

 40°. Its specific gravity at that temperature would have been 

 1.030, or specifically 30 per cent, heavier than the sea water of our 

 own coasts. Could two such currents of water meet anywhere 

 at sea, except as u^Dper and under currents ? If water that freezes 

 at 32°, that grows light and remains on the surface as you cool it 

 below 39°, is prevented from freezing in our great fresh-water 

 lakes by vertical circulation, how much more would both vertical 

 and horizontal circulation prevent congelation in the open polar 



