THE TEADE WIND. 139 



September. — The N.E. Trade has generally increased in force, but is 

 blowing in nearly the same part of the district as in August. 



The Southerly winds North of the Equator continue to blow over the 

 same part of the sea as in August ; they also continue to draw into South- 

 Westerly winds as they approach the area of lowest pressure near the 

 West Coast of Africa ; their force has very decidedly decreased since 

 August. To the Southward of the Equator the S.E. Trade has decidedly 

 increased in force since August. The gradient for North-Easterly winds 

 seems to be steeper than for South-Easterly of the same force; this appears 

 to be common in other months also, and probably indicates that the N.E. 

 Trade gradient gets some of its supply of air from a downward movement, 

 whilst that part of the S.E. Trade with which we are dealing is probably 

 more entirely a horizontal motion of air. The dry, transparent, gusty 

 nature of the Northern part of the N.E. Trade probably points to the 

 same fact. 



October. — The N.E. Trade has advanced several degrees to the South- 

 ward, especially on the Eastern side of the district, and now prevails to 

 8° N. ; by this change it has extended over that part of the sea where 

 there is the highest temperature of both air and sea, so that instead of 

 North- Westerly and South- Westerly winds blowing into the area of highest 

 temperature, there is a hot N.E. wind blowing from it ! The N.E. Trade 

 has increased in force since September. 



The S.E. Trade prevails to 8° N., and there is no prevailing South- 

 westerly wind, it having given way to the N.E. Trade. Tlie S.E. Trade 

 has very much decreased in force since September, especially in the 

 Southern part of the district. Easterly squalls, veering from N.E. to S.E., 

 are very common between the Trades in October. 



November. — The N.E. Trade has advanced about 2° to the Southward 

 since October, and now prevails to 6° N. ; it still extends over the hottest 

 area of air and sea, and, as in October, has not that tendency to draw into 

 a North- Westerly wind near the Coast of Africa which it had in previous 

 months. In the most Northern part of the district it does become more 

 Northerly near Africa, but in about 10° N. it becomes more Easterly again, 

 and draws away from the land. The N.E. Trade has decreased in force 

 near its Northern limits since October, and increased near its Southern 

 limits ; in the extreme North of the district the percentages of South- 

 Easterly and South- Westerly winds have much increased since October, 

 which seems to show that the Northern limit of the Trade is not very far 

 North of the district in November. 



The S.E. Trade prevails to 6° N., and, as in October, has fewer South- 

 westerly winds at its Northern verge than in previous months. South of 

 the Equator it has increased in force since October, but scarcely chanc^ed 

 to the Northward of it. 



December. — The N.E. Trade has advanced 2° to the Southward since 

 November, and now prevails to 4° N. Near the African land the wind 

 again becomes light, and more Northerly, changing even to North-Westerly 

 between 6° and 10° N., but the prevailing wind still blows North-Easterly, 

 from the hottest air and sea. The most remarkable feature in the direction 

 of the N.E. Trade in December is its prevalence at East between 10° and 



