THE ATMOSPHERE. 73 



directions at the bottom, the motion of the water would be down- 

 ward, so is the motion of the air in this calm zone. 



102. The barometer, in this calm region, is said to stand higher 

 than it does either to the north or to the south of it ; and this is 

 another proof as to the banking up here of the atmosphere, and 

 pressure from its downward motion. 



103. Following our imaginary particle of air from the north 

 across this calm belt, we now feel it moving on the surface of the 

 earth as the northeast trade-wind ; and as such it continues, till it 

 arrives near the equator, w^here it meets a like hypothetical par- 

 ticle, which, starting from the south at the same time the other 

 started from the north pole, has blown as the southeast trade-wind. 



104. Here, at this equatorial place of meeting, there is another 

 conflict of winds and another calm region, for a. northeast and 

 southeast wind can not blow at the same time in the same place. 

 The two particles have been put in motion by the same power ; 

 they meet with equal force ; and, therefore, at their place of meet- 

 ing, are stopped in their course. Here, therefore, there is a calm 

 belt. 



105. Warmed now by the heat of the sun, and pressed on each 

 side by the wdiole force of the northeast and southeast trades, 

 these two hypothetical particles, taken as the type of the whole, 

 cease to move onward and ascend. This operation is the reverse 

 of that which took place at the meeting (^ 100) near the parallel 

 of 30°. 



106. This imaginary particle then, having ascended to the up- 

 per regions of the atmosphere again, travels there counter to the 

 southeast trades, until it meets, near the calm belt of Capricorn, 

 another particle from the south pole ; here there is a descent as 

 before (§ 101); it then (§ 98) flows on toward the south pole as 

 a surface wind from the northw^est. 



Entering the polar regions obliquely, it is pressed upon by sim- 

 ilar particles flowing in oblique currents across every meridian ; 

 and here again is a calm place or node ; for, as our imaginary par- 

 ticle approaches the parallels near the polar calms more and more 

 obhquely, it, with all the rest, is whirled about the pole in a con- 

 tinued circular gale ; finally, reaching the vortex or the calm place, 

 it is carried upward to the regions of atmosphere above, whence 

 it commences again its circuit to the north as an upper current, as 



