376 



HYDROGRAPHY. 



Having thus given the extent of the several Trade Winds of the 

 Oceans, I shall give those of the Monsoons, which will also be found 

 represented on the map. 



The Monsoons differ materially in character from the Trade Winds. 

 They are more equable, without the squalls, and undergo little varia- 

 tion during the day and night. They have their regular increase 

 and decrease until they cease. They are more allied to the land and 

 sea breezes, and result from the same cause. Indeed, they may be 

 said to be such on a large scale, having a duration of several months? 

 instead of occurring daily. Every one who has experienced the Mon- 

 soons, cannot fail to have been struck with the great difference be- 

 tween them and the Trade Winds. The most remarkable Monsoons 

 are those of the China Seas and Indian Ocean, called the Northeast 

 and Southwest. They prevail between the Equator and the latitude 

 of 30° north, extending on the land as well as over the neighboring 

 seas. Each, on an average, has a duration of five months in either 

 direction ; at the changes, which occupy two months, variable winds 

 occur. 



There appears to be much exaggeration about their constancy and 

 their course. The cause assigned for them is undoubtedly the true 

 one, — that of the heating of the immense areas of land of the Asiatic 

 continent by the sun, rarefying them, and thus drawing towards 

 them currents of air from the southwest to restore the equilibrium. 



It may occur to others, as it has to myself, why should not this air 

 be supplied from the cold countries of the north, which are nearer, 

 and should be induced to seek these warm and rarefied areas ? 



By an inspection of the map, we find ample reason why this cannot 

 take place. We will there perceive that the highest chain of moun- 

 tains in the w r orld stretches across the whole of Asia, from east to 

 west, creating an insuperable barrier to the winds coming from the 

 cold regions of the north beyond ; and therefore the air is induced 

 from the southwest, to flow towards the heated areas of Hindostan 

 to restore the equilibrium ; further it cannot go. 



To the north of this range of mountains also lies the Desert of 

 Gobi, and on the west is the high table-land of Iran, as well as that 

 of Syria, and the Sahara of Africa. These all induce the denser and 

 colder air from the mountains on the east, and from the north, to 

 supply the rarefied area which exists in those places. On the sun's 

 return to southern declination, these parts become cooled, when the 



