Proximate Causes of certain Winds and Storms. 275 



ashes were whirled into the air at the latter or western extremity, 

 and brought down to the surface at the eastern.* 



(d.) " On the western coasts of both continents, a wind from the 

 west prevails."^ This passage is quoted from a work which, along 

 with valuable matter, contains a share of inconclusive argument 

 from facts incorrectly stated. These westerly winds are created by a 

 cause, having a close resemblance to that to which the trade winds 

 are ascribed by Halley. They are unquestionably movements of 

 the air in vortices revolving eastward below, and westward above. J 

 Their existence proves nothing absolutely, but lends a degree of 

 probability to the accuracy of the views advanced in this paper. 

 Why may not the eastern and western or trade winds resemble each 



other in their causes, effects, and all the circumstances of their pro- 

 gress. 



(e.) The coolness and freshness of the air within the limits of the 

 trades so much exceeding what might be expected from the latitude, 

 is a proof that it is affected by currents flowing down from above, 

 and altogether incompatible with the idea that they are ground cur- 

 rents of which the cold returning upper current flows off towards the 

 poles. " Nothing equals the beauty and mildness of the equinoctial 

 region on the ocean."§ " In these winds there is something so ex- 

 hilarating that one with difficulty believes so much vapor exists as the 

 hygrometer indicates."|| "The climate of these (the Sandwich) 

 islands is far more cool than might be supposed, judging from their 

 latitude."1T He attributes the circumstance to the prevalence of the 

 north-east trade winds. 



(/.) The infrequency of rain within the limits of the trades is an- 

 other proof of the mixture of the upper and lower strata of the air, 

 by ascending and descending currents. Rain is produced by the 

 sudden mixture of air of very different temperatures charged with 

 moisture ; effected, as there is good reason to believe, by the estab- 

 lishment of a vortex or horizontal whirlwind upon the spot where it 



* See for the above facts. Von Buch, in loc. cit. and Philosophical Mag. Vol. xl. 

 t Daniell's Meteorological Essays. 



I See account of the land and sea breeze?. 



§ Humboldt ; sec also his remarks on the temperature of the air, which are too 

 *°ng to be extracted. 



II CaldcleugrTs observations in Brazil and on the equator. 

 ^ Stewart's Journal. 



