t. 



30 THE OCEAN 



gions where the earth revolves rapidly, have 

 a tendency to lag behind and flov^ towards the 

 west. This cold water being confined by the 

 continent in its westward flow and by the Gulf 

 Stream to the east, follows along the coast to- 

 wards the south, and is known as the Arctic 

 Current. Although a vast amount of this 

 cold water reaches the tropics and gradually 

 mingles with the warmer waters, yet even a 

 larger amount comes from the Antarctic seas, 

 for the contour of the bottom of the ocean's 

 bed prevents a large part of the north polar 

 water from flowing south. In the case of the 

 air these same things occur and it is these phe- 

 nomena which produce the strong easterly 

 trade winds near the equator and the stormy 

 westerly winds in the north and south polar 

 regions, so in reality the trade winds them- 

 selves and the ocean currents which they pro- 

 duce are both due to the revolution of the 

 earth upon its axis and to the fact that cold 

 water or air contracts and sinks while warm 

 water or air expands and rises. 



As the air is not prevented from moving 

 freely by obstacles in its path the wind cur- 



