SURFACE CURRENTS 59 



lent winds, to a north-easterly direction. This diver- 

 sion may be helped by the pressure of the continuation 

 of the cold Labrador Current, a much weaker current, 

 composed of water of very low temperature and salinity, 

 derived from the melted ice and snow of the Arctic 

 regions as far north as Baffin Bay. About 50 N. 

 much of this current turns from south-east to an 

 easterly, and eventually north-easterly, direction ; but 

 a part swings round Labrador to south-west, and skirts 

 the north coasts of the eastern United States, greatly 

 lowering their temperature. To some extent, however, 

 the cold water in this region is attributable to up- 

 welling caused by the pull of the Gulf Stream. The 

 boundary between the hot and cold waters of the Gulf 

 Stream and Labrador Current swings north and south, 

 according to the predominant winds ; it is said to be 

 so sharp sometimes that a ship's bow may be in 

 green cold water of arctic origin, while her stern is 

 in warm blue water from the Gulf. 



The Gulf Stream gradually assumes a more easterly 

 trend. It has been calculated that at about 40 W. it 

 has lost the velocity and temperature which its water 

 acquired in the Gulf. This water still continues, 

 however, to travel east, but the driving power now is 

 not the original head of water, but the prevailing 

 south-west winds of this region. It is therefore no 

 longer a " stream," but is better termed the North 

 Atlantic Drift. Between 40 W. and 20 W., the pull 

 of those winds round the high-pressure area, which 

 culminate in the trade winds, draw off much surface 

 water past the Azores in a south-easterly and southerly 

 direction. But the main axis of the drift, being outside 

 their influence, passes north-east, striking the Faeroe 

 and Shetland Islands. Its influence is well shown on 

 both isotherms and isohalines (Charts III. and IV.), as 



