92 TRADE-WINDS. 



trouble and difficulty do ships experience in 

 crossing it. 



It has already been explained that about lat. 30, 

 the upper current of wind from the south descends. 

 At the same point the upper current from the 

 north also descends. They cut through each other, 

 and the point where these two cut each other is the 

 northern limit of the north-east trade-winds. The 

 same explanation holds in regard to the southern 

 limit of the south-east trades. 



In the accompanying diagram the arrows within 

 the circle point out the direction of the north-east 

 and the south-east " trades " between the tropics of 

 cancer and Capricorn, and also the counter currents 

 to the north and south of these, while the arrows 

 around the circle show how counter currents meet 

 and rise, or descend, and produce the calm belts. 



We have hitherto enlarged chiefly on the grand 

 currents of the atmosphere, and on those modifying 

 causes and effects which are perpetual. Let us now 

 turn to the consideration of those winds which are 

 produced by local causes, and the effects of which 

 are partial. 



And here we are induced to revert to the Gulf 

 Stream, which has been already referred to as a 

 local disturber of the regular flow of the atmos- 

 phere. This immense body of heated water, pass- 

 ing through cold regions of the sea, has the effect of 

 causing the most violent storms. The hurricanes 

 of the West Indies are among the most violent in 



