208 ON THE GALES OF 



than the atmospheric air, causes levity by its ad- 

 mixture. 



Yet the density arising from inferiority of situa- 

 tion in the stratum of air immediately over the Gulf, 

 compared with that of the volumes of the fluid lying 

 upon the mountainous country beyond it, may to a 

 certain extent, more than make up for the influence 

 of the heat and moisture derived from the Gulf : but 

 violent winds must arise so soon as these causes pre- 

 dominate over atmospheric pressure, so far as to ad- 

 mit the cold air of the mountains to be heavier. 



When instead of the air covering a small portion 

 of the mountainous or table land in Spanish Ame- 

 rica, that of the whole north-eastern portion of the 

 North American continent, is excited into motion, 

 the effects cannot but be equally powerful, and much 

 more permanent. The air of the adjoining country 

 first precipitates itself upon the surface of the Gulf, 

 then that from more distant parts. Thus a current 

 from the north-eastward is produced below. In the 

 interim the air displaced by this current rises, and 

 being confined by the high land of Spanish Ame- 

 rica, and in part possibly by the trade winds, from 

 passing off in any southerly course, it is of necessity 

 forced to proceed over our part of the continent, 

 forming a south-western current above us. At the 

 same time its capacity for heat being increased by 

 the rarefaction arising from its altitude, much of its 

 moisture will be precipitated, and the lower stratum 

 of the south-western current mixing with the upper 

 stratum of the cold north-eastern current below, 



