134 THE PHYSICAL GEOGRAPHY OF THE SEA. 



cultivated there in great perfection. No climate of the temperate 

 zone will be found to surpass in salubrity that of this Piedmont 

 trans-Mississippi country. 



336. By such trains of thought and reasoning as are here sketch- 

 ed, and by such facts and circumstances as are stated above, I 

 have been brought to regard the extra-tropical regions of the north- 

 ern hemisphere as standing in the relation of a condenser to a 

 grand steam machine (§ 168), the boiler of which is in the region 

 of the southeast trade- winds, and to consider the trade- winds of 

 this hemisphere as performing the like office for the regions beyond 

 Capricorn. 



33 7» The calm zone of Capricorn is the duplicate of that of 

 Cancer, and the winds flow from it as they do from that, both 

 north and south ; but with this difference : that on the polar side 

 of the Capricorn belt they prevail from the northwest instead of 

 the southwest, and on the equatorial side from the southeast in- 

 stead of the northeast. 



338. Now if it be true that the vapor of the nortlieast trade- 

 winds is condensed in the extra-tropical regions of the southern 

 liemisphere, the following path, on account of the effect of diurnal 

 rotation of the earth upon the course of the winds, would repre- 

 sent the mean circuit of a portion of the atmosphere moving ac- 

 cording to the general system of its circulation over the Pacific 

 Ocean, viz., coming down from the north as an upper current, and 

 appearing on the surface of the earth in about longitude 120° 

 west, and near the tropic of Cancer, it would here commence to 

 blow the northeast trade-winds of that region. 



339. To make this clear, see Plate YII., on which I have mark- 

 ed the course of such vapor-bearing winds ; A being a breadth or 

 swath of winds in the northeast trades ; B, the same wind as the 

 upper and counter-current to the southeast trades ; and C, the 

 same wind after it has descended in the calm belt of Capricorn, 

 and come out on the polar side thereof, as the rain winds and pre- 

 vailing northwest winds of the extra-tropical regions of the south- 

 ern hemisphere. 



340. This, as the northeast trades, is the evaporating wind. 

 As the northeast trade-w^ind, it sweeps over a great waste of 

 waters lying between the tropic of Cancer and the equator. 



