482 PASSAGES OVER THE ATLANTIC. 



In several of the squares the number of observations is so small that it 

 would be useless to give them on monthly charts for each '2f square, as 

 was done for Square 3 ; they have therefore been sifted into spaces of 

 2° of latitude by 5° of longitude. This method has the advantage of 

 enabling us to represent a larger space on the same chart ; and in most 

 instances the spaces seem to be small enough to point out any differences 

 which actually exist. 



Captain Toynbee remarks : — Having thus given a general view of the 

 work we have in hand, I will now refer to the monthly diagrams, and also 

 call attention to some interesting facts which have struck me in writing 

 the remarks. Perhaps I ought first to say that in several instances the 

 number of observations is so small that the Isobars, Isotherms, and Wind 

 and Current arrows are not always so correct as a larger amount of data 

 would make them ; still in Square 3 (which is the centre of the district) 

 and in Squares 39, 301, and 302, there is a large number of observations, 

 so that the general result is satisfactory ; for we find that the same month 

 in different years has very much the same kind of Wind and Weather. I 

 may add that though all data have been referred to the centre of the space 

 to which they belong, it sometimes happens that nearly all the observations 

 have been taken on one side of that space. 



In the first place, then, it will be seen that we are dealing with a part 

 of the sea where the two Trades are always meeting, though the latitude 

 in which they meet varies with the season. This work therefore gives the 

 meteorologist a constant opportunity for studying the motion of air where 

 two air currents meet, and also the weather resulting therefrom. 



Besides the meeting of two currents of air there are also two currents of 

 water, which are mainly produced by the Trade Winds, and apparently 

 increased in speed by the drift of water forced against Africa by the 

 winter gales of each hemisphere. The direction of the Trades tends to draw 

 water away from the coast of Africa, and as the land prevents an influx of 

 water from the Eastward, there is a third current or back-drift to the 

 Eastward into the Gulf of Guinea, to replace the water drawn away by the 

 Trade Winds. This is the well known Guinea Current, which seems to be 

 chiefly the result of gravity. 



It must be remembered that Winds are named after the direction from 

 which they come, whilst Currents are named after the direction towards 

 which they go ; for instance, an arrow pointing to the North- Westward 

 represents a S.E. wind, but a N.W. current; therefore, in the diagrams 

 the tails of the wind-arrrows and the heads of the current -arrows point 

 towards the points of the compass after which they are named. 



Kemarks on Winds, of the regions under consideration, for each month, 

 are given in pages 136 — 140. On the Currents : North African Current, 

 313—315, Guinea Current, 332—334, North Equatorial Current, 344—345, 

 the South Equatorial Current is described in pages 347 — 353. Beaufort's 

 Scale of Wind (Force) is described in pag«a 103 — 104. 



