10 



THE NOETH-EAST ATLANTIC. 



pole to pole was at a uniform temperature of 40° Fahr., a temperature which was 

 wrongly assumed to be that of the point of maximum density. 



In the North Atlantic, as in other seas, the temperature diminishes from the 

 surfiice downwards, but not uniformly. In certain strata the fall is measured only 

 by tenths of a degree for hundreds of yards, whereas in the liquid masses farther 

 down there are sudden falls of several degrees. These serious differences can 

 only be explained by the volumes of water which here meet from various quarters. 

 Thus, from the dej^th of 50 to 500 fathoms, the waters of the Atlantic between 

 Ireland and Rockall cool very slowly, for this zone is covered entirely by the warm 

 mass flowing from the tropical seas. But from 500 to 750 and 1,000 fathoms the 



Fig. 5. — Fall of Tempeeatuke in the Lower Depths of the Atlantic, West of Iueland. 



According to Sir Wyville Thomson. 



TEMP, p, 



64-4 



FATHOMS 273 



I3G7 16+0 



2IC7 24S2 



diminution of temperature is much more rapid, owing to the influx of cold water 

 from the polar regions flowing slowly in a direction contrary to that of the 

 warmer upper currents. Lastly, the fall of temperature from 1,000 fathoms to the 

 bottom again becomes very gradual. At a depth of 2,435 fathoms, the greatest 

 reached by the plummet and thermometers of the Porcupine, the naturalists 

 observed a temperature of 35° ; but this was due west of Brittany, which is 

 beyond the limits of the North-east Atlantic proper. 



A study of these lower temperatures has shown that a sharp contrast is pre- 

 sented by the two basins of the North Atlantic on either side of the submarine 

 bank between Scotland and Ireland. In the west the ocean is occupied by waters 



