( i57 ] 



e.-THE AFRICAIT MONSOONS. 



(80.) The influence of the land upon the Trade Winds, and the inter- 

 vening Calms, is very powerful on the Eastern side of the Atlantic; and 

 the peculiar configuration of the Coast of Guinea, trending as it does along 

 the very axis or line of division of the N . rthern and Southern Wind sys- 

 tems, causes a different set of phenomena to arise. During that part of 

 the year when the sun is in the Southern Hemisphere, the Trades and 

 Calms follow the normal or usual course, as it is then exerting its maximum 

 force on the sea with its low absorptive and radiative powers ; but when, 

 during the Northern summer, it is raising the temperature of the land of 

 the Guinea Coast, a new phase arises from the heated atmosphere over 

 the land drawing the wind towards it ; and instead of a S.E. or N.B. wind, 

 we have a South and S.W. wind occurring with great regularity. Major 

 Eennell says, "In the space lengthwise, between Cape Verde and Cape 

 Mesurado, and in certain places to the extent of 200 miles off shore (150 

 off Sierra Leone), a regular change of winds and currents takes place, 

 according to the seasons. That is to say, a N.E. or North wind and S.E. 

 current, from September to June ; and, in the rest of the year, a S.W. 

 wind and N.E. or Northerly currents, in effect a Monsoon, and this extends, 

 in respect of the wind, nearly through the whole space between the two 

 continents.* 



(81.) In Dampier's Discourse on the Trade Winds, and his illustrative 

 Chart (1697), we find a solution of the origin of these S.W. winds, which 

 is that still held to be most feasible. It is, that they are derived from the 

 S.E. Trades, and not from a diversion of the N.E. Trades. This also was 

 suggested in the " Mercantile Marine Magazine," of 1856, the data being 

 derived from Maury's charts. An important element in determining the 

 reality or otherwise of this suggestion is the position of the Calms. Are 

 they interposed between the N.E. Trade and Monsoon, or between the 

 Monsoon and S.E. Trade? But this consideration may not have great 

 weight in this region of calms, and besides the probability of this origin is 

 increased by the data for the direction of the S.E. Trade, which is shown 

 not to blow with regularity to the East of a line joining Cape Palmas and 

 Angola. 



(82.) There is another conclusive evidence of the Westerly extension of 

 the Monsoons in the Easterly current which is met with almost constantly 

 during the seasons of their prevalence. These are very persistent as far as 

 longitude 40° W., and are at times encountered as far North as latitude 16°, 

 but more usually between lats. 6° and 11° N. This origin of the anomalous 

 Guinea Current was indicated in our chart of the Atlantic Ocean, published 

 in 1858. A similar current is shown to exist in the Pacific Ocean, West 



• The existence and character of this S.W. African Monsoon we^ thus early recog- 

 nized and named (at the latter end of the eighteenth century). The term " newly- 

 discovered" Monsoons, given to them by our American friends, is therefore not quite 

 applicable. 



