IN PBODUCINa A8CENDIKQ ATMOSPHERIC CURBENTS. 



207 



of this extraordinary wind we have no means of determining, 

 the requisite meteorological information not having been 

 furnished, but it is stated to come from the desert, and 

 to continue but a short time ; it cannot therefore be taken 

 as evidence of the existence of such an ascending current 

 within the desert, as is under consideration. Such evidence 

 as it furnishes is indeed in favour of the non-existence of 

 such a current, or of the means of producing one. If suffi- 

 cient vapour existed in the part, it would be carried up by 

 the Simoom, and would produce continued rain, as it does 

 in rainy localities. 



The Harmattan is a wind that blows on the surface of the 

 desert, from the interior towards the Atlantic Ocean, passing 

 for some distance over the sea. It. is irregular in its occur- 

 rence, although more frequent in our winter than at other 

 times. It blows with considerable force, and often lasts for 

 a number of days. The following is a description of this 

 wind by Milner. He says — " The Harmattan, a periodical 

 wind from the desert, differs remarkably from the Simoom. 

 It blows from the interior of the great Sahara, from the 

 north-east over Senegambia and Guinea, to that part of 

 the coast of Africa that is between Cape Verde, in fifteen 

 degrees of north latitude, and Cape Lopez, in one degree 

 of south latitude, a coast line of upwards of 2,000 miles. 

 It occurs during December, January, and February, generally 

 three or four times in the season. It comes on indiscrimi- 

 nately at any hour of the day, at any time of the tide, or 

 at any period of the moon, continuing sometimes only a day 

 or two, at other times five or six days, and it has been 

 known to last for upwards of a fortnight. It blows out to 

 sea for ten or twelve leagues. Extreme dryness is another 

 property of the Harmattan : no dew falls during its con- 

 tinuance, nor is there the least appearance of moisture in 

 the atmosphere." This account of the Harmattan shows that 

 it blows over the surface of the earth, and from the desert, 



