DISTRIBUTION OF R^INS. 131 



per hour ; at the poles, the amount of motion is zero ; and between 

 the poles and the equator, every degree of velocity between zero 

 and a thousand miles per hour is represented. The cold currents 

 of air starting from the poles and moving equatorward, as they 

 come up over those portions of the earth moving at a rapid veloci- 

 ty, unable to keep pace with that velocity, fall back, and the con- 

 sequence is, in the northern hemisphere, the wind blowing down 

 from the north, instead of keeping pace with the earth's accelera- 

 tion in its loAver latitudes, falls buck, and gives us a wind from the 

 northeast, known as the northeast trade wind. How is it in the 

 southern hemisphere ? The wind blowing from the south towards 

 the equator, unable to keep pace with the motion of the earth, as it 

 comes up into those regions where the motion is rapid, foils back 

 in a similar manner, and gives us a wind from the southeast, 

 known as the southeast trade wind. Thus we have two»winds, 

 the northeast trade wind in the northern hemisphere, and the 

 southeast trade wind in the southern hemisphere. These winds 

 prevail from about 30° north to 30° south of the equator. 



As these winds come together at the equator and mingle, there 

 is formed what is called the equatorial calm belt — that belt from 

 which the heated currents of air rise. This is not a fixed belt, 

 extending around the globe at the equator, but moves north and 

 south with the sun.. When the sun passes north of the equator, 

 this belt moves north ; when the sun goes south, it moves south 

 also ; and thus it sways backward and forward by a gradual 

 movement throughout the entire year. 



These trade winds constitute what are known as "periodical 

 winds." And while speaking of these, I may as well notice an- 

 other set of periodical winds, which, unlike those that blow in the 

 same dii'ection throughout the entire year, prevail in one direction 

 during one half, and in the other direction dui'ing the other half of 

 the year. I refer to the monsoons of the Indian Ocean. During 

 the summer nionths, when the sun is north of the equator, the 

 lands forming the southern portion of Asia become very highly 

 heated, and the winds from the Indian Ocean prevail in the direc- 

 tion of the heated belts of air thus produced. As the heated air 

 rises the colder air of the ocean rushes in to take its place. The 

 result is, that from the month of April to October, the prevailing 

 wind in the Indian Ocean is from the southwest. Durinor the re- 

 maining portion of the year, the southern part of Africa becomes 

 highly heated, and ascensional currents of warm air ai'e produced ; 



