3 TIIP] TROPICAL WORLD. 



rarefied air, as it rises into the higher regions, completely over- 

 powers the usual course of the trade wind, and changes it into 

 the south-western monsoon, which blows from May to Sep- 

 tember. 



Hence, during the summer months, the saturated sea wind, 

 striking against the western ghauts, brings rain to the coast of 

 Malabar, while the opposite coast of Coromandel remains dry ; 

 but the inverse takes place when, from the sun's declining to 

 the south, the north-east trade wind resumes its sway. 



Similar deflections from the ordinary course of the trade 

 winds occur also on the coast of Guinea (5° N. Lat.), in the 

 Mexican Grulf, and in that part of the Pacific which borders on 

 Central America, through the influence of the heated plains of 

 Africa, Utah, Texas, and New Mexico, and have a similar in- 

 fluence on the distribution of moisture. Thus the sea monsoon, 

 which prevails during the summer months on the coast of 

 northern Gruinea, carries a rainy season over the land as far as 

 the eighteenth or nineteenth degree of northern latitude, and 

 fertilises a vast extent of country which, from its position on the 

 western side of an immense continent, would otherwise have 

 been as naked and barren as the Sahara. 



As the tropical rains, though generally confined only to part 

 of the year, and then only to a few hours of the day, fall in so 

 much greater abundance than under our constantly drooping 

 skies, it may naturally be supposed that the single showers 

 must be proportionally violent. Descending in streams so close 

 and so dense that the level ground, unable to absorb it suffi- 

 ciently fast, is covered with a sheet of water, the rain rushes 

 down the hill-sides in a volume that wears channels in the sur- 

 face. For hours together the noise of the torrent, as it beats 

 upon the trees and bursts upon the roofs, occasions an uproar 

 that drowns the ordinary voice and renders sleep impossible. 

 In Bombay nearly nine inches of rain have been known to fall 

 in one day, and twelve inches in Calcutta, or nearly half the 

 mean annual quantity of rain on the east coast of England. 

 During one single storm which Castelnau witnessed at Pebas, 

 on the Amazon, there fell not less than thirty inches of rain — 

 nearly as much as the annual supply of our west coast. The 

 hollow trunk of an enormous tree in an exposed situation gave 

 the French traveller the means of accurate measurement. 



