GULF STEEAM— TEMPERATURE. 



11 



whose temperature to their lowest depths nowhere falls to freezing point, whereas 

 in the east the warm water is found only on the surface, resting on liquid strata at 

 a glacial temperature, and less charged with salt. 



In the broad open passage between the Fiiroer and Shetland groups the sound- 

 ings have clearly revealed the presence of the lower mass of cold waters flowing 

 beneath the warmer upper strata, and it has even been found possible proximately 

 to determine the limits of this vast submarine stream. On either side of the cold 

 zone the temperature falls nearly at the same ratio as in the neighbouring ocean. 

 At a depth of 820 fathoms the warmth of the water is still about 41° Fahr., 

 whereas in the cold zone this temperature of 41° is already reached at a depth 

 of 191 fathoms, the thermometer marking 32° Fahr. at 328 fathoms. There is 



Fig. 6. — Fall of the Temperature in the Warm and Cold Waters. 

 According to Sir Wy\"iUe Thomson. 



altogether a mean difference of 13° between the waters of the cold zone and those 

 of the surrounding seas. 



Judging from its direction, this volume of cold water seems to be a continuation 

 of the polar current which passes east ot Spitzbergen and Bear Island, afterwards 

 sinking below the warmer strata, and ultimately disappearing in the depths. On 

 reaching the elevation connecting the Faroer bank with the Hebrides, the cold 

 zone terminates suddenly, as clearly shown by the various soundings that have 

 been made here. Yet the cold waters at this point rise somewhat higher than the 

 submarine ridge, and might pass it but for the resistance of the warm current. 

 Unable to overcome this obstacle, they are obliged to recede, borne back by the 

 upper current, which they in return rapidly cool, reducing it to a shallow surface 

 stratum.* 



* Mohn, in Petermann's Mitthcllungen, i. 1878. 



