152 THE SEASON WHY. 



" They shall be as the morning clcv A, and as the early dew that passeth away, 



as the chaff that is driven with the whirlwind out of the floor, and as 



the smoke out of the chimney." HOSEA xni. 



Trade winds are vast currents of air, which sweep round tJio 

 globe over a belt of some 12,000 miles in width. 



669. What is the cause oftrale ivinds ? 



The air over the tropical regions becomes heated and ascends ; it 

 then diverges in two high currents, one towards the north, and the 

 other towards the south pole, where, being cooled, it again descends, 

 and returns towards the equator to replace the air as it ascends 

 therefrom. There is, therefore, a constant revolution of vast cur- 

 rents of air between the tropics and the poles, producing north and 

 south winds. 



670. Why do the trade winds How from east to west, 

 though, in their origin, their direction is from north to south 

 and from south to north ? 



Because, as the north and south winds blow towards the equator, 

 they are affected by the revolution of the earth from west to east. 

 As the two winds from the poles approach the equator, they are 

 gradually diverted from their northerly and southerly course, to an 

 easterly direction, by the revolution of the earth. 



671. Why is there a prevalence of calms at the equator? 

 Because, as the north and the south winds move towards the 



equator, they drive before them volumes of atmosphere, which, 

 meeting in opposite directions, resist and counterpoise each other, 

 and abide in a state of stillness between the north and south- 

 easterly winds, one on the north and the other on the south of the 

 equator. 



672. What are monsoons ? 



Monsoons are periodical winds which blow at a given period of 

 the year from one quarter of the compass, and in another period of 

 the year from the opposite quarter of the compass. 



673. What is the cause of monsoons ? 



Monsoons are caused by changes in the position of the sun. 

 When the sun is in the southern hemisphere, it produces a north- 

 east wind, and when it is in the northern hemisphere, a north-west 

 wind. The north-east monsoon blows from November to March, 



