MAGNETISM AND CIRCULATION OF THE ATMOSPHERE. 



Ill 



in the relation of a condenser to a grand steam machine (^ 120), 

 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. 



199. The calm zone of Capricorn is the duphcate 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. 



Now if it be true that the vapor of the northeast trade-winds 

 IS condensed in the extra-tropical regions of the southern hemi- 

 sphere, the following path, on account of the effect of diurnal ro- 

 tation of the earth upon the course of the winds, would represent 

 the mean circuit of a portion of the atmosphere moving according 

 to the general system of its circulation over the Pacific Ocean, 

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

 pearing on the surface of the earth in about longitude 1 20° west, 

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

 the northeast trade-winds of that region. 



200. To make this clear, see Plate VIL, 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 wunds and pre- 

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

 ern hemisphere. 



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

 northeast trade-wind, it sweeps over a great waste of waters lying 

 between the tropic of Cancer and the equator. 



201. Meeting no land in this long oblique track over the tepid 

 waters of a tropical sea, it would, if such were its route, arrive 

 somewhere about the meridian of 140° or 150° west, at the belt 

 of equatorial calms, which always divides the northeast from the 

 southeast trade-winds. Here, depositing a portion of its vapor as 

 it ascends, it would, with the residuum, take, on account of diurnal 

 rotation, a course in the upper region of the atmosphere to the 

 southeast, as far as the calms of Capricorn. Here it descends 



