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produce the Permanent and Periodic Winds. 44i7 



believe that such trifling variations as these, at such a distance 

 apart, and on opposite sides of the Himalayas and the high table- 

 land of Thibet, could produce such very marked results as the 

 north-east and south-west monsoons, even if we were to set on 

 one side the utter want of dependence that can be placed on com- 

 parative barometric observations so taken (L'Asie Centrale, vol. i. 

 p. 80), and even if Humboldt's evidence as to fact was not con- 

 clusive. But since the Himalayas form an actual boundary to 

 the monsoon region, the cause of the monsoons is clearly not to 

 be sought either on the Gobi or at Barnaul. 



If now we for a few minutes put on one side the theory that these 

 constant winds, whether trade-winds or monsoons, are due to the 

 expansion caused by heat, we cannot but be struck with a certain 

 remarkable relation between the points to which they tend ; these 

 points are all distinguished by their excessive rainfall. The 

 trade-winds in both oceans tend to the equator : the region of 

 equatorial calms has received from all physical geographers 

 the name of the zone of constant precipitation : Maury speaks 

 of the rain as " so copious that the fresh water is sometimes 

 found standing in pools on the sea." The south-east trade 

 blows home on the coast of South America with great force as a 

 wind due east; and the volume of water discharged into the sea 

 by the Amazon and the Orinoco is a convincing proof of the 

 enormous quantity which falls on the area of their drainage; 

 whilst the succession of rainy seasons at different distances in- 

 land seems to bear on the changes of wind in the interior in a 

 very extraordinary manner. Bates says that at Santarem " from 

 August to February very little rain falls, and the sky is cloud- 

 less for weeks together, the fresh breezes from the sea, nearly 

 400 miles distant, moderating the great heat of the sun. The 

 wind is sometimes so strong for days together, that it is difficult 

 to make way against it in walking along the streets." (Natu- 

 ralist on the Amazons, vol. ii. p. 13.) At Ega, on the contrary, 

 " from the middle of October to the beginning of January the 

 second wet season prevails/'' and " the second dry season comes 

 on in January, and lasts throughout February." (Ibid. p. 223.) 

 During this dry season there is a change in the state of things 

 at Santarem : " the fine weather breaks up, often with great 

 suddenness, about the beginning of February. Violent squalls 

 from the west, or the opposite direction to the trade-wind, then 

 occur. . . . They are accompanied with terrific electric explosions, 

 the sharp claps of thunder falling almost simultaneously with 

 the blinding flashes of lightning. Torrents of rain follow the 

 first outbreak ; the wind then gradually abates, and the rain 

 subsides into a steady drizzle." (Ibid. p. 25.) The heaviest 

 rains of }he year fall (at Santarem) in April, May, and June; 



