THE TRADE WINDS. 81 



constituents of the "breath of life" is effected, and the 

 purer oxygen of the "land of the sunny south" is dif- 

 fused in healthful gales over the colder climes of the 

 north. The waters, too, evaporated from the great 

 central Atlantic Ocean, or the far Pacific, are thus car- 

 ried over the wide-spread continents, and poured in fer- 

 tilising showers upon distant lands. 



How magnificent are the operations of nature ! The 

 air is not much warmed by the radiations of caloric pass- 

 ing from the sun to the earth ; but the surface soil is 

 heated by its power of absorbing these rays. The tem- 

 perature of the air next the earth is raised, and we thus 

 have the circulation of those beneficial currents which 

 are so remarkably regular in the Trade Winds. The air 

 heated within the tropics would ascend directly to the 

 poles, were the earth at rest, but being in motion, those 

 great aerial currents the Trade Winds are produced, 

 and the periodical monsoons are due to the same cause. 

 A similar circulation, quite independent of the ordinary 

 tidal movement, takes place also in the earth-girdling 

 oceau. The water, warmed, by convection, from the hot 

 surface of the tropical lands, sets across the Atlantic 

 from the Gulf of Mexico ; and being under the influence 

 of the two forces gravity and motion it illustrates the 

 parallelogram of forces, and flowing along the diago- 

 nal, reaches our own shores : the genial influences of 

 the gulf stream produce that tempered climate which 

 distinguishes our insular home. Here we have two im- 

 mense influences produced by one agency, rendering 

 those parts of the earth habitable and fertile, which but 

 for these great results would sorrow in the cheerless 

 aspect of an eternal winter. 



The beautiful phenomenon of the formation of dew is 

 also distinctly connected with the peculiar properties 

 which we have been studying. When from the bright blue 

 vault of heaven, the sparkling constellations shower their 

 mild light over the earth, the flowers of the garden and 



