Qn the Gales of the Atlantic States. 353 



m 



sure, as well as on heat, and it does not follow, that air 

 which may be heated in consequence of its proximity to the 

 earth, will give place to colder air from above. The pres- 

 sure of the atmosphere varying with the elevation, one stra- 

 tum of air may be as much rarer by the diminution of pres- 

 sure consequent to its altitude, as denser by the cold, con- 

 sequent to its remoteness from the earth, and another may 

 be as much denser by the; increased pressure arising from 

 it^ proximity to the earth, as rarer by being warmer. 

 Hence when unequally heated, different strata of the at- 

 niosphere do not always disturb each other. Yet after a 

 time, the rarefaction in the lower stratum, by greater heat, 

 niay so far exceed that in an upper stratum attendant on an 

 inferior degree of pressure, that this stratum may prepon- 

 derate, and begin to descend. Whenever such a move- 

 nient commences, it must proceed with increasing velocity ; 

 for the pressure on the upper stratum and of course its den- 

 sity and weight, increases as h falls; while the density and 

 Weight of the lower stratum, must lessen as it rises. Hence 

 the change is, at times, so much accelerated, as to assume 

 the characteristics of a tornado, squall or hurricane. In 

 like manner may we suppose, the predominant gales of our 

 climate to originate. Dr. Franklin long ago noticed, that 

 north-eastern gales are felt in the south-westernmost por- 

 tions of the continent first, the time of their commencement 

 bem^ found later, as the place of observation is more 

 to the leeward. This need not surprise us, as it is evident 

 that a current may be produced either by a pressure from 

 behind, or by a hiatus consequent to a removal of a portion 

 of the fluid from before. 



, The Gulf of Mexico is an immense body of water, warm 

 |n the first place by its latitude, in the second place by its 

 being a receptacle of the current produced by the trade 

 Winds, which blow in such a direction as to propel the warm 

 Water of the torrid zone into it, causing it to overflow and 

 produce the celebrated Gulf Stream, by the ejection to the 

 north-east of the excess received from the south-east. This 

 stream runs away to the northward and eastward of the 

 United States, producing an unnatural warmth in the ocean, 

 as Well as an impetus, which, according to Humboldt, is not 

 expended, until the current reaches the shores of Africa, 

 ^nd even mixes with the parent flood under the equator. 



