§ 033-035. SEA KOUTES, CALM BELT:>, ETC. ^;j9 



in the northern hemisphere, and the land surface is also much 

 greater on our side of the equator. The action of the sun upon 

 these unequally absorbing and radiating surfaces in and behind, 

 or to the northward of the northeast trades, tends to check these 

 winds, and to draw in large volumes of the atmosphere, that other- 

 wise would be moved by them, to supply the partial vacuum 

 made by the heat of the sun, as it pours down its rays upon the 

 vast plains of burning sands and unequally heated land surfaces 

 in our overheated hemisphere. The northwest winds of the 

 southern are also, it may be inferred, stronger than the southwest 

 winds of the northern hemisphere. 



633. That the southeast trade-winds should, as observations 



^vhy the southeast (8 843) havc showu, bc stronD;er than the north- 

 trades are the stron- ^ . , . , . 



ger. east trade-wnids, is due m part also to the well-es- 



tablished fact that the southern (§ 446) is cooler than the north- 

 ern hemisphere. The isothermal lines of Dove show that the air 

 of the southeast is also cooler than the air of the northeast trade- 

 winds. Being cooler, the air from the cool side would, for pal- 

 pable causes, rush with greater velocity into the equatorial calm 

 belt than should the lighter air from the warmer or northern 

 side. The fact that the air in the lower latitudes of the southern 

 hemisphere is the cooler will assist to explain many other con- 

 trasts presented by the meteorological conditions on opposite 

 sides of the equator. Plate XIII. shows that we have more 

 calms and more fogs, more rains and more gales, with more 

 thunder, on one side than the other, and that the atmosphere pre- 

 serves its condition of unstable equilibrium with much more uni- 

 formity, being subject to changes less frequent and violent on the 

 south side of the equator than on the north side. 



634. The highest summer temperature in the world is to be 

 Their iinifoi-mity of fouud iu the cxtra-troplcal countries of the north, 

 ttmperatiu-e. rp]^^ grcatcst cxtrcmes of temperature are also to be 

 found among the valleys of the extra- tropical north. In the ex- 

 tra-tropical south there is but little land, few valleys, and much 

 water ; consequently the temperature is more uniform, changes are 

 less sudden, and the consequent commotions in the air less violent. 



635. Following up these facts with their suggestions, we dis- 

 Th3 mean place of the covcr the key to many phenomena which before 

 equatorial calm belt. ^^.^^^ lockcd up lu "the chambcrs of the south." 



