346 Capt. Toynbee on the Circulation $c. [June 15, 



into the S.E. trades without any intervening calm. In fact this heated 

 part of Africa seems at this season to have the power of bringing the N.E. 

 trades to an end in about 17 N. lat. between the islands and the main, 

 instead of 13 N. lat. outside, and of causing an indraft from the west- 

 ward ; it also gradually turns the S.E. trade which blows near Africa into 

 a S.W. wind, which we may suppose finds its way into the upper stratum 

 of air over this heated land. Part of this S.W. monsoon seems to be 

 formed of the damp cloudy air which exists in the doldrums, whilst the 

 rest is evidently formed of clearer air another evidence that it is part of 

 the S.E. trades. 



It would be interesting to treat in a similar way a few logs of American 

 ships leaving in July, and supplied with standard instruments, since they 

 might show how far to the westward the barometer continues to range 

 higher, and we have Maury's works to prove that the N.E. trades do 

 extend nearer to the equator in more western longitudes. 



Having thus considered the curves of the outward passage from England 

 with respect to their difference when further east or further west, we will 

 view them in a north and south direction. It will be noticed that the 

 lowest barometer occurs in the belt of doldrums, between the trades ; and 

 by comparing the outward with the homeward route it will be seen, as is 

 well known, that this belt is further north in July than in March. It is 

 interesting, however, to see that the lowest barometer travels north or 

 south with the belt of doldrums, showing that its cause must be sought for 

 there, and not in centrifugal force, which might be supposed to fix it at 

 the equator. 



The sailor is naturally led to ask how it is that the barometer is lower 

 here, a zone towards which two trade-winds are pouring in an immense 

 body of air along the earth's surface, and in nearly opposite directions; for 

 near the equator the trades draw more north and south. "We suppose there 

 can be but one answer, viz. that here the air rises, and forms those two 

 upper currents which rush towards the poles, above and counter to the 

 trade-winds. Maury tells us that the so-called African dust is really South 

 American, and that much more rain falls in the northern than in the 

 southern hemisphere, from which he argues that the air which formed the 

 S.E. trades, having traversed more sea and picked up more moisture, rises 

 in these doldrums, and travels to the N.E. above the N.E. trades'; and 

 vice versd, that the N.E. trades travel to the S.E. above the S.E. trades. 

 He does not say how they pass each other, neither can we, but we have 

 strong evidence of a current of air travelling above and in opposite direc- 

 tion to the trade-winds, because we generally see the high clouds travelling 

 in that direction. We have, however, as it were, even seen the air ascend- 

 ing ; for on the 15th of March, 1865, in 4 18' N. lat. and 20 33' W. long., 

 when we had light fleecy clouds passing over us from the N.E., and we lay 

 becalmed and roasting, longing for the trades, my chief officer came and 

 reported to me with a hopeful countenance that he had seen these light 



