UPPER AND UNDER CURRENTS OF OCEAN. 177 



There is an under-current setting from the At- 

 lantic, northward through Davis' Straits, into the 

 Arctic Ocean, and a surface-current setting out. 

 The fact is proved beyond a doubt by the observa- 

 tions of arctic explorers, who have seen immense 

 icebergs drifting rapidly northward against a 

 strong current. This apparent anomaly could only 

 be accounted for by the fact that a powerful under- 

 current carried them northward ; and as at least 

 seven times more of these bergs must have been 

 under than above water, we can easily understand 

 how the under-current, acting on the larger mass 

 of each berg, had power to carry it against the sur- 

 face-current. 



This under-current is warm, while the upper- 

 current is cold. Now we know that, according to 

 Nature's laws, heated water, like heated air, rises 

 to the surface, and cold water sinks to the bottom. 

 How, then, comes this warm current to be under- 

 neath the cold, as soundings have proved it to be ? 

 It is owing to the fact that the under-current is 

 much salter, and therefore heavier (despite its 

 warmth), than the surface-current ; which latter, 

 being mingled with the drainage and ice-masses of 

 the arctic regions, is comparatively fresh, and 

 therefore light as well as cold. 



The hot and salt waters of the tropics are carried 

 north by the Gulf Stream. There are here two 

 counteracting agents at work. Heat inclines 

 the Gulf Stream to rise ; saltness inclines it to 



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