78 THE PHYSICAL GEOGRAPHY OF THE SEA. 



time the other started from the north pole, has blown as the south- 

 east trade-wind. 



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

 conflict of winds and another calm ^'egion, 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. 



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

 side by the whole 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 (§ 130) near the parallel of 30°. 



137. 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 (§ 131) ; it then (§ 126) flows on toward the south pole as 

 a surface wind from the northwest. 



138. Entering the polar regions obliquely, it is pressed upon by 

 similar particles flow^ing 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 

 obliquely, 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 far as the calm belt of Capricorn; here it encounters (§ 137) its 

 fellow from the north (§ 126) ; they stop, descend, and flow out as 

 surface currents (§ 132), the one with which the imagination is 

 traveling, to the equatorial calm as the southeast trade-wind ; here 

 (§ 135) it ascends, traveling thence to the calm belt of Cancer as 

 an upper current counter to the northeast trades. Here (§ 130 

 and 129) it ceases to be an upper current, but, descending (§ 131), 

 travels on with the southwest passage-winds toward the pole. 



139. Now the course we have imagined an atom of air to take 



