PORTER’S JOURNAL. 
>S:£ 
clination, as he happens to be at present; but by running the vye 
over the chart the mystery is solved. 
It is well known that the trade winds blow from the eastward 
to the westward throughout the year, but undergoing some slight 
variations from local causes, or the change of the sun’s place 
in the ecliptic; and those winds, it is generally admitted, are 
caused by the highly rarefied state of the air between the tropics? 
and the passage of the sun from east to west, or rather the earth’s 
rotatory motion from west to east, it follows that a current of 
cold air must rush to those points where theair is most rarefied, to 
restore the eqilibrium. And as the coast of Africa to the north of 
the equator, and between Cape Verd and Sierra Leone, projects 
west, to within 10 or 12 degrees of the usual track of vessels cross'** 
ing the line bound to the southward, and as the trade-winds, before 
they reach this point, pass over a tract of land, extending from the 
Gulf of Arabia to the Atlantic, and equal in width to 65 degrees, 
it may be presumed that they must contract in their passage a 
great intensity of heat, of which they lose but a small portion 
before reaching the track of vessels; it may therefore be expect¬ 
ed, even if facts did not prove it to be the case, that the most in- 
tense heat of the trades experienced by vessels is near the most 
westerly projection of Africa, or between the latitudes of 5° and 
12° north. 
From Sierra Leone the land trends to the eastward for about 25 
degrees, and forms that part of the ocean called the Gulph of 
Guinea, the bottom of which lies in about 12° east longitude; 
consequently a space of ocean extends between the continent and 
the ship (when between the line and lat. 5° N.) of upwards 
of 35 degrees; and as the trades in passing over the continent 
here from the Indian seas have only a passage of 30°, and conse¬ 
quently contract only a proportionable degree of heat, and as it 
might be expected that much of it would be lost before they 
reach the ship, it seems natural to suppose that they would in¬ 
cline toward the north, to restore the equilibrium (destroyed by 
the highly rarefied air from the projecting point of Africa), and 
thus produce the cool and refreshing S.E. trade winds. When 
the sun is to the north of the equator, the S.E. trades are to be 
