OCEANIC CIRCULATION. 233 



Eastern Atlantic ' in the same latitudes ; c and the 

 thickness of the stratum that undergoes superheating 

 during the summer is about the same. ... At 

 the depth of a hundred fathoms, in the Atlantic as in 

 the Mediterranean, the effect of the superheating seems 

 extinct, the thermometer standing at about 53 degrees ; 

 and beneath this ' (in the Atlantic only), 'there is a slow 

 and tolerably uniform reduction at the rate of about 

 two-thirds of a degree for every fathom, down to 

 700, at which depth the thermometer registers 49 

 degrees. But the rate of reduction then suddenly 

 changes in the most marked manner ; the thermometer 

 showing a fall of no less than nine degrees in the next 

 200 fathoms, so that at 900 fathoms it stands at 40 

 degrees. Beneath this depth the reduction again be- 

 comes very gradual ; the temperatures shown at 1,500, 

 2,000, and 2,435 fathoms (the last being the deepest 

 reliable temperature sounding yet obtained) being, 

 respectively, 38, 37, and 36 degrees.' 



Thus, there can be no possible question that the 

 depths of the Atlantic are occupied by a vast current 

 much colder than the deep sea temperature due to the 

 latitude, and, therefore necessarily flowing from the 

 arctic towards the tropical seas. 



Such are the broad facts of the Atlantic circulation. 

 We have a surface circulation whose general features 

 are such as have been described, and are generally ad- 

 .mitted, though a dispute has arisen as to a question of 

 nomenclature ; and then we have a general submarine 

 ' set ' of water from the arctic regions towards the 



