B68 SUPPLEMENTARY REMARKS ON WINDS. ETC. 



The shade temperature rarely exceeds 80°, except during the Harmattan. 

 This blows from S.E. to N.N.E. off the land, and may be expected between 

 October and February. From November to February, the winds are 

 variable, but chiefly N.E. and N.E. by N. 



Red Dust. — The tropical regions of the African coast, between Cape 

 Bojador and Cape Blanco, present to contemplation the Sahara, con- 

 sidered as the most ejctensive desert on the globe. It consists of in- 

 adhesive sands, which are driven about by the winds, and chiefly by those 

 from N.E., by which they are disturbed and carried to an astonishing 

 distance, sometimes falling on vessels hundreds of miles out to sea. Thia 

 phenomenon is more amply discussed at the end of this work. 



Currents. — It has been already shown, in pages 312 — 315, 321, and 

 323 — 324, that the prevailing currents set from North to South along the 

 whole coast. Along the edge of the Bank of Arguin, as far as its western 

 extremity, this direction is constant ; and in the rainy season, should any 

 deviation be experienced, it may be relied on to happen very seldom. One 

 proof of this may be adduced. On July 13th, 1830, when the wreck of 

 the Medusa was found by the brig Argus, after 13 days absence from the 

 frigate, it was abreast of Portandik, at 45 miles from the shore, a distance 

 of 90 miles, and nearly on the meridian of the place where she was lost. 

 It must, therefore, have driven at the rate of 7 miles per day along 

 the coast. 



SENEGAL RIVER.— Winds.— The Winds are not at all dangerous in 

 the navigation of the coasts of the Senegal. They blow between East and 

 North during the greater part of the year ; and as, in the rainy season 

 (June to September), the squalls generally come from the S.E., those 

 vessels in the road which cannot depend on their ground tackle can easily 

 get under way, and return to their anchorage after the squall is over, as 

 the S.W. winds which succeed are generally very weak. In the fine 

 season, strong N.W. winds sometimes occur, but are of short duration. 

 In the dry season, the sea breezes blow regularly, but the cUmate is then 

 very unhealthy. 



Currents. — As noted above, the general and almost constant direction 

 of the current is along the coast from North to South, as far as the mouth 

 of the Senegal, but abreast of this opening, and in a space of several 

 miles to seaward, the river tides affect the general uniformity of thia 

 current. 



The prevailing currents between the Senegal and Cape Verde follow the 

 direction of the coast, in the same manner as those to the northward ; and 

 the idea of a current setting violently into the Bay of Yof is by some 

 stated to be altogether false. 



Dakar. — The climate is unhealthy, and epidemics of yellow fever are 

 occasionally experienced. The rainy season is from June to December, 

 and Tornados occur chiefly in July. 



GAMBIA RIVER.— The Climate is naturally insalubrious, and all 

 Europeans who can do so leave it during the bad season, when fevers, 

 rheumatism, and dysentery are prevalent. The worst months are 

 September, October, and November ; from December to March it is 

 considered to be fairly healthy. Vessels stationed here are recommended 



