2 THE TROPICAL WORLD. 



a coolness to the atmosphere, the refreshing effects of which 

 are felt wherever the sea wind blows. There can, therefore, be 

 no doubt that, if the greater part of the tropical ocean were 

 converted into land, the heat of the torrid zone would be far 

 more intolerable than it is. 



The restless breezes and currents, the perpetual migrations of 

 the air and waters, perform a no less important part in cooling 

 the equatorial and warming the temperate regions of the globe. 

 Karefied by the intense heat of a vertical sun, the equatorial 

 air-stream ascends in perpendicular columns high above the 

 surface of the earth, and thence flows off towards the poles ; 

 while, to fill up the void, cold air-currents come rushing from 

 the arctic and antarctic regions. 



If caloric were the sole agent on which the direction of these 

 antagonistic air-currents depended, they would naturally flow 

 to the north and south ; but the rotation of the earth gradually 

 diverts them to the east and west, and thus the cold air- 

 tjurrents, or polar streams, ultimately change into the trade 

 winds which regularly blow over the greater part of the tropical 

 ocean from east to west, and materially contribute, by their 

 refreshing coolness, to the health and comfort of the navigator 

 whom they waft over the equatorial seas. 



While the polar air-currents, though gradually warming as 

 they advance, thus mitigate the heat of the torrid zone, the 

 opposite equatorial breezes, which reach our coasts as moist 

 south-westerly or westerly winds, soften the cold of our winters, 

 and clothe our fields with a lively verdure during the greater 

 part of the year. How truly magnificent is this grand system 

 of the winds, which, by the constant interchange of heat and 

 cold which it produces, thus imparts to one zone the beneficial 

 influence of another, and renders both far more fit to be in- 

 habited by civilized man. The Greek navigators rendered 

 homage to ^olus, but they were far from having any idea of 

 the admirable laws which govern the unstable, ever-fluctuating 

 domains of the ' Grod of the Winds.' 



The same unequal influence of solar warmth under the line 

 and at the poles, which sets the air in constant motion, also 

 compels the waters of the ocean to perpetual migrations, and 

 produces those wonderful marine currents which like the analo- 

 gous atmospheric streams, furrow in opposite directions the 



