508 CURRENTS AND WHALING. 



In the Mozambique Channel, a current sets northward, along the 

 western shore of Madagascar ; while on the coast of Africa opposite, 

 the water sets almost continually to the south. But on the same 

 coast to the north of the line, a weak current is found setting towards 

 the Persian Gulf, and thus causing the current we have stated to run 

 southwards on the Malabar coast. 



The Equatorial Stream of the South Atlantic may be cited as fur- 

 nishing a good instance of the effect that currents may produce on 

 climate. It always includes the island of Anno Bon within its influ- 

 ence, while St. Thomas, in longitude 6£° E., and immediately under 

 the equator, is only affected by it at times, and Prince's Island is 

 never reached by it. The manner in which their climates are influ- 

 enced by this circumstance is thus described by Colonel Sabine : 



"The occasional advance of the cold water of the Equatorial Car- 

 rent to the island of St. Thomas, may assist in explaining an apparent 

 peculiarity in the climate of that island, when compared with the 

 climate of the coast of Western Africa generally. At all the British 

 possessions, from the Gambia, in latitude 13° N., to the forts on the 

 Gold Coast, the months of June, July, and August, are accounted 

 unhealthy; whilst at St. Thomas's, on the contrary, they are the most 

 healthy in the year to Europeans, although they are not so to the 

 negroes, who suffer much from colds and rheumatisms during- their 

 continuance. It has been shown that the water of the Equatorial 

 Current is from ten to twelve degrees colder than that of the Gulf 

 of Guinea, and that its northern border, which at other seasons 

 passes the meridian of St. Thomas at a distance of from one hundred 

 and twenty to one hundred and eighty miles south of its southern 

 extremity, was found in June in contact, or very nearly so, with the 

 island itself; and it is not improbable, from a consideration of the 

 causes which occasion its advance towards the equator when the sun 

 is in its northern signs, that in July it may extend so far as even to 

 include the whole island of St. Thomas within its limits. 



" The temperature of the air is known to be immediately dependent 

 on that of the surface water of the sea, and to be influenced nearly to 

 the full extent of any alteration that may take place therein. In 

 crossing the Bight of Biafra, from Cape Formosa to St. Thomas's, 

 the air, over the surface of the Guinea Current, observed in the shade 

 and to windward, at sunrise, noon, and sunset, averaged 81J°, the 

 extremes being 79° and 83J° ; whilst in the passage from the river 

 Gaboon to Ascension, over the Equatorial Current, the air averaged 



