742 WINDSOFTHEGLOBE. 



We have seen already that on the Atlantic the division-line between the N. E. trade 

 and the S. W. monsoon of the African coast runs about 12° N., the trade losing 

 its regularity even at 14° N. in July. On the continent this line runs more north. 

 The country to the north, having the whole year N. winds, is rainless, or nearly so ; 

 it is the Sahara or Great Desert ; south is the Soudan, the country of Agriculture, 

 where ve"-etation is more and more luxuriant the more we advance southward. 

 This is caused by the longer continuance of the rain They reach in the middle 

 of the summer to about 17°, but in spring and autumn the division-line is more to 

 the south, and south of this line there are southerly winds and rains. 



The African traveller Eohlfs remarks that "in the beginning of July we traversed 

 the Titiimna or Great Steppe between 16° and 17° where a luxuriant vegetation is 

 found. I noticed a remarkable change in the direction of the wind, instead of the 

 N. E., E. and S. E. we had before, the S. W. was prevailing now. Later, when we 

 came to the country with tropical rains (Kouka) the S. W. was still prevailing, though 

 the rain-clouds came from the S. E."^ The woodland (Mimosa trees) began at 

 about 152° N. on the route he traversed. Very similar are the conditions in Nubia. 

 Irregular tropical rains fall as far north as 19° N., further there is a country of 

 prairies or savannah (openings) and still further south the woodland begins. The 

 observations at Sennaar show very well the character of the climate in S. Nubia: 

 N. winds in winter, S. winds in summer, both largely prevailing. (See Plate 7.) 

 The remarkable frequence of calms when the sun passes the zenith is also to be 

 noticed. So, for example, at Schimmedru, 18° 57' N., there were 37 per cent, of 

 calms in April, 62 per cent, in May, and 47 per cent, in June. At Kouka, 12° 52', 

 N. Rohlfs observed 46 per cent, of calms in July, 66 per cent, in August, and 51 

 per cent, in September. The sun is at its zenith at Schimmedru in May and at 

 Kouka in August. 



Goree exhibits the change of monsoon in Western Africa. 



Further S., on the coast of Guinea, the winds are from the same direction the 

 whole year ; this is the region of the S. W. winds. The daily period is very well 

 marked tlie whole year, the winds being N. W. in the night and morning, and 

 S. W. in the middle of the day. 



On the shores of the Mediterranean the direction of the wind is not the same as 

 in the desert. Especially in Algeria, where the N. W. is most frequent winter 

 and summer. (See Plates 5, 6, and 7.) At the coast stations of Egypt (Alex- 

 andria and Port Said) W. and S. W. prevail in winter, and N. and N. W. in 

 summer. There is a belt of highest pressure in winter, and, besides this, there are 

 winds from the land to the sea in the cold season. Farther south, N. W. and N. 

 winds prevail the whole year, as at Cairo, Ismailia, Suez. 



» See Petermann's Mittheilungen, Ergauzungsheft, N. 25. 



