§ 227-229. THE ATMOSPHERE. 33 



The air sloughed oflf (§ 204 [7~\ ), a different process of slouojliino^ off" and 



from the counter . i 1 • • tt 1 • -■ 



trades, moist air. tummg bacK IS gomg on. Here the winds are 

 blowing toward the poles ; they are going from parallels of large 

 to parallels of smaller circumference, while the upper return cur- 

 rent is doing the reverse ; it is widening out with the increasing 

 circumference of parallels, and creating room for more air, while 

 the narrowing current below is crowding out and sloughing off 

 air for its winds. 



227. In the other case (§ 224), it was the heavy dry air that 

 The air sloughed off was sloughcd off to joiu the winds below. In this 



from the upper trade . .., . ^ ^• 1 -i 



current dry. casc it IS the moist auQ lightest air that is crowded 



out to join the current above. 



228. This is particularly the case in the southern hemisphere, 

 The meteorological whcrc, entirely around between the parallels of 40*^ 

 SgSuSnfoSS and 60° or 65°, all, or nearly all, is water. In this 

 ''^'''" great austral band the winds are in contact with, 

 an evaporating surface all the time. Aqueous vapor is very much 

 lighter than atmospheric air; as this vapor rises, it becomes en- 

 tangled with the particles of air, some of which it carries up with 

 it, thus producing, through, the horizontal flow of air with the 

 winds, numerous little ascending columns. As these columns of 

 air and vapor go up, the superincumbent pressure decreases, the 

 air expands and cools, causing precipitation or condensation of 

 the vapor. The heat that is set free during this process expands 

 the air still further, thus causing here and there in those regions, 

 and wherever it may chance to be raining, intumescenses, so to 

 speak, from the wind stratum below ; the upper current, sweep- 

 ing over these protuberances, bears them off in its course to- 

 ward the equator, and thus we have another turning back — a con- 

 stant mingling. The curved arrows, hj k and h' j' h' ^ are intend- 

 ed, on the '' diagram of the winds" (Plate I.), to represent this ris- 

 ing up from the counter trades and turning back with the upper 

 current. 



229. Let us imagine the air to be visible, that we could see 

 Supposing the air thcsc different strata of winds, and the air as it is 

 Sa? wouidTe'*pS sloughed off froui one stratum to join the other. 

 rp°pe?and\owercS! ^^ cau ouly likcu the spectacle that would be pre- 

 7^°*^* sented between the upper and the lower stratum of 

 these winds to the combing of a succession of long waves as 



