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the line of the equator you will notice that for 

 more than three-quarters of the distance it 

 passes through the water. The water, as we 

 have explained in the last chapter, becomes 

 gradually heated to a considerable depth, and 

 when once saturated with heat is slow to give 

 it up. It can easily be seen that there will be 

 a zone extending each way from the equator 

 for a certain distance that will become more 

 intensely heated than any other parts of the 

 earth, with the exception of certain circum- 

 scribed portions of the land. The result is 

 that this heated equatorial zone is constantly 

 sending up warm air caused by the inrush of 

 colder air, which is heavier than the air at the 

 equator, expanded by the heat. The warm air 

 at the equator is forced up into the higher 

 regions of the atmosphere, and here it over- 

 flows each way, north and south, causing a 

 current of air in the upper regions counter to 

 that of the lower. As it travels north and 

 south it gradually drops as it becomes cooler, 

 and finally at some point north and south its 

 course is changed and it flows in again toward 

 the equator. As a matter of fact, the trade 

 winds do not flow apparently from the north 

 and south directly toward the equator, but in 

 an oblique direction. On the north side of the 

 equator we have a northeasterly wind, and a 

 southeasterly wind on the south side. This is 

 caused by the rotation of the earth from west 



