352 Oh the Gales of the Atlantic States 



Art. XX. — On the Gales experienced in the Atlantic 

 States of JVortk' America, By Robert Hare, M. D. 



[Read May 14th, 1822, before the Academy of Natural Sciences of Phila- 

 delphia, from whose Journal it is copied.] 



Of the gales experienced in the Atlantic States of 

 North America, those fron:) the north-east and north-west 

 are by far the most influential: the one remarkable for its 

 dryness; the other for its humidity. During a north-west- 

 ern gale, the sky, unless at its commencement, is always 

 pecuharly clear, and not only water, but Ice evaporates rap- 

 idly. A north-east wind, when it approaches at all to the 

 nature of a durable gale, is always accompanied by clouds, 

 and usually by rain or snow. The object of the following 

 essay, is to account for this striking diversity of character. 



When heat is unequally applied to the lower strata of a 

 non-elastic fluid, the consequent difference of density (re- 

 sulting from the unequal expansion,) soon causes move* 

 ments, by which the colder portions change places with the 

 warmer. These being cooled, resume their previous situa- 

 tion, and are again displaced by being again made warmer. 

 Thus, the temperatures reversing the situations, and these 

 reversing the temperatures, a circulation is kept up tendmg 

 to restore the equilibrium. Precisely similar would be the 

 case with our atmosphere, were it not an elastic fluid, and 

 dependant for its density on pressure, as well as heat. Its 

 temperature would be far more uniform than at present, and ^ ^ 



all its variations would be gradual- An interchange of po- 

 sition would incessantly take place, between the colder air 

 of the upper regions, and the warmer, and of course lighter 

 air near the earth's surface, where the most heat is evolved * 



from the solar rays. Currents would incessantly set from , 



the poles to the equator below, and from the equator to the ^ 



poles above* Such ciirrents would constitute our only | 



winds, unless where mountains might produce some devia- 

 tions. Violent gales, squalls, or tornadoes, would never 

 ensue. Gentler movements would anticipate them. _ But 

 the actual character of the air with respect to elasticity, is 

 diametrically the opposite of that which we have supposed- 

 It is perfectly elastic. Its density is dependant on pres- • 



