172 PPIYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOPtOLOGY. 



of it cliiefly in three ways : some is carried off by convection in tlie 

 air ; some by evaporation ; and some by radiation ; and such is the 

 interference of clouds with this last-named process, that we are 

 told that dm-ing the rainy season in intertropical countries, as on 

 the coast of Africa, there is often not radiation enough to produce 

 the phenomena of land and sea breezes. The absence of dew in 

 cloudy nights is a familiar instance of the anti-radiating influence 

 of clouds. The southern hemisphere, bemg so much more aqueous, 

 is no doubt much more enveloped with clouds where its oceans lie, 

 than is the northern where its continents repose, and therefore it is 

 that one hemisphere radiates more than the other. 



369. Thus, by observing and discussing, by resorting to the 



Facts and pearls, force of rcasou aud to the j^rocesses of induction, 



we have gathered for the theory that favom^s the air-crossings at 



the calm belts fact upon fact, which, like pearls for the necklace, 



seemed only to require a string to hang them together. 



CHAPTEK yill. 



§ 370-409. — CURRENTS or the sea. 



§370. We here set out with the postulate that the sea, as well 

 . Obedient to order, as the air, has its system of circulation, and that this 

 system whatever it be, and wherever its channels lie, whether in 

 the Avaters at or below the smiace, is in obedience to law. The 

 sea, by the circulation of its waters, doubtless has its offices to 

 perform in the terrestrial economy ; and when we see the currents 

 in the ocean ninnmg hither and thither, we feel that they were 

 not put in motion without a cause. On the contrary, we know 

 they move in obedience to some law of Nature, be it recorded 

 down in the depths below, never so far beyond the reach of human 

 ken ; and being a law of Natm-e, we know who gave it, and that 

 neither chance nor accident had anything to do mth its enactment. 

 Nature grants us all that this postulate demands, repeating it to 

 us in many forms of expression : she utters it in the blade of green 

 grass which she causes to grow in climates and soils made kind 

 and genial by warmth and moisture that some cm-rent of the sea or 

 air has conveyed far away from imder a tropical sun. She mm'- 

 murs it out in the cooling current of the north ; the whales of the 

 sea tell of it (§ 158) ; and all its inhabitants proclaim it. 



