Oceanic and Atmospheric Currents. 51 



the surface of the rotating globe. We have currents of cold 

 air flowing from high into low latitudes in a westerly direction, 

 and currents of warm air passing in an easterly direction from 

 the Tropics into the temperate and the polar regions. The 

 effect of these currents moving in opposite directions is seen in 

 the creation of several belts or areas of calms, one near 

 the Equator, one at each Pole, and one near the parallels 

 of lat. 30 . In accordance with theory, the belts of calms 

 are due to an encounter which takes place in about lat. 

 30 between equatorial and polar currents. The former, 

 coming from the Equator in the character of upper-currents, 

 are supposed to descend in that latitude to the surface of the 

 ocean, and to continue their course towards the polar regions 

 as under -currents, having acquired an easterly tendency 

 owing to the gradually decreasing rotatory velocity of the areas 

 over which they flow, until, finally, they are arrested as they 

 approach the Poles by the friction of the earth's surface. The 

 latter, coming from the polar regions as upper-currents, descend 

 near the same latitude towards the surface of the ocean, and 

 continue their course towards the Equator as under-currents, 

 gradually losing their westerly tendency until, in the vicinity of 

 the Equator, they commence to rotate with the earth's surface 

 and are no longer felt as easterly winds, thus producing the 

 Equatorial belt of calms. 



A current moving from the Equator towards the Pole will 

 not acquire a decided tendency towards the east until it reaches 

 the parallel of lat. 30 , as the diameter of rotation decreases very 

 slowly at first, its total decrease between lat. 30 and 45 being 

 greater than that between the Equator and lat. 30 (Fig. 13). 

 It will, therefore, not manifest itself as a strong easterly current 

 until it crosses the 30th parallel. On the other hand, a current 

 flowing from the Pole towards the Equator, while having from the 

 outset a strong tendency to lag behind in a westerly direction, 



