62 THE PHYSICAL GEOGRAPHY OF THE SEA. 



175. Now, what should attract these storms to the Gulf Stream, 

 More observations in IS a questioH which jet remains to be satisfactorily 

 s?r^eam°a* dS(Sra- ^Tiswered. A good scrics of slmultancous baro- 

 *"°^- metric observations within and on either side of 

 the Gulf Stream is a great desideratum in the meteorology of 

 the Atlantic. At the equator, where the trade-winds meet and 

 ascend, where the air is loaded with moisture, and the vapor from 

 the warm waters below condensed into the equatorial cloud-ring 

 above, we have a low barometer. 



176. How is it with the Gulf Stream when these storms from 

 Certain storms make ^ight and Icft burst in upou it, and, turning about, 

 for it and follow it. ^ourse aloug with it ? Its waters are warm ; they 

 give off vapor rapidly ; and, were this vapor visible to an ob- 

 server in the moon, he no doubt would, on a winter's day espe- 

 cially, be able to trace out by the mist in the air the path of the 

 Gulf Stream through the sea. 



177. Let us consider the effect of vapor upon winds, and then 

 How aqueous vapor thc importaucc of the observations proposed (§ 175) 



assists in producing .,, , i-i,, ' , -\ \ 



winds. Will perhaps be better appreciated. Aqueous va- 



por assists in at least five, perhaps six ways to put air in motion 

 and produce winds. (1.) By evaporation the air is cooled ; by 

 cooling its specific gravity is changed, and, consequently, here is 

 one cause of movement in the air, as is manifest in the tendency 

 of the cooled air to flow off, and of warmer and lighter to take its 

 place. (2.) Excepting hydrogen and ammonia, there is no gas so 

 light as aqueous vapor, its weight being to common air in the 

 proportion of nearly 5 to 8 ; consequently, as soon as it is formed 

 it commences to rise ; and, as each vesicle of vapor may be liken- 

 ed, in the movements which it produces in the air, to a balloon as 

 it rises, it will be readily perceived how these vaporous particles, 

 as they ascend, become entangled with those of the air, and so, car- 

 rying them along, upward currents are produced : thus the wind 

 is called on to rush in below, that the supply for the upward 

 movement may be kept up. (3.) The vapor, being lighter than air, 

 presses it out, and, as it were, takes its place, causing the barometer 

 to fall : thus again an in-rush or wind is called for below. (4.) Ar- 

 rived in the cloud-region, this vapor, being condensed, liberates 

 the latent heat which it borrowed from the air and water below ; 

 which heat being now set free and made sensible, raises the tem- 



