THE ATMOSPHERE. 81 



observation as to direction of tlie wind, reason would teach us 

 to look for the prevailing winds on each side of this calm belt to 

 be/rowi it. 



212. Tlie equatorial calm belt. — Following our imaginary particle 

 of air, however, from the north across this calm belt of Cancer, 

 we now perceive it moving on the surface of the earth as the 

 north-east trade-wind ; and as such it continues till it arrives 

 near the equator, where it meets a like hypothetical particle, 

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

 from the north pole, has blown as the south-east trade-wind. 

 Here, at this equatorial place of meeting, there is another conflict 

 of winds and another calm region, for a north-east and south-east 

 wind cannot blow in the same place and at the same time. The 

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

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

 they are arrested in their course. Here, therefore, there is a 

 calm belt, as well as at Capricorn and Cancer. Warmed now by 

 the heat of the sun, and of vapour in the process of condensa- 

 tion, and pressed on each side by the whole force of the north- 

 east and south-east trades, these two hj^pothetical 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 (§ 210) near the belt between the parallels 

 of 30°-35°. 



213. The calm helt of Capricorn. — This imaginary particle then, 

 having ascended to the upper regions of the atmosphere again, 

 travels there counter to the south-east trades, until it meets, 

 near the calm belt of Capricorn, another particle from the south 

 pole; here there is a descent as before. (§ 210); it then (§ 211) 

 flows on towards the south pole as a surface wind from the 

 north-west. 



214. The'polar calms and the return current. — Entering the polar 

 regions obliquely, it is pressed upon by similar particles flowing 

 in oblique currents across every meridian ; and here again is a 

 calm place or node ; for, as our imaginary particle approaches 

 the parallels near the polar calms more and more obliquely, it, 

 with all the rest, is whirled about the pole in a continued 

 circular gale ; finally, reaching the vortex of the calm place, it is 

 carried upward to the regions above, whence it commences again 

 its flow to the north as an upper current, as far as the calm belt 

 of Capricorn; here it encounters (§ 213) its fellow from the 



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