Thus far as to the cause and progress of the Nile’s inundation in our northern hemisphere; but so much light and confirmation is to be drawn from our consideration of the remainder of the sun’s journey southward, that I am persuaded my following him thither will require no apology to my philosophic or inquisitive reader.
Immediately after the sun has passed the Line he begins the rainy season to the southward, still as he approaches the zenith of each place; but the situation and necessities of this country being varied, the manner of promoting the inundation is changed. A high chain of mountains run from about 6° south all along the middle of the continent towards the Cape of Good Hope, and intersects the southern part of the peninsula nearly in the same manner that the river Nile does the northern. A strong wind from the south, stopping the progress of the condensed vapours, dashes them against the cold summits of this ridge of mountains, and forms many rivers which escape in the direction either east or west, as the level presents itself. If this is towards the west, they fall down the sides of the mountains into the Atlantic, and if on the east, into the Indian Ocean. Now all these would be useless to man, were the Etesian winds to reign, as one would think must be the case, analogous to what passes in Egypt; nay, if any one wind prevailed, these rivers, swelled with rains, would not be navigable, but another wise and providential disposition has remedied this.
The clouds, drawn by the violent action of the sun, are condensed, then broken, and fall as rain on the top of this high ridge, and swell every river, while a wind from the ocean on the east blows like a monsoon up each of these streams in a direction contrary to their current, during the whole time of the inundation, and this enables boats to ascend into the western parts of Sofala, and the interior country to the mountains, where lies the gold. The same effect, from the same cause, is produced on the western side towards the Atlantic; the high ridge of mountains being placed between the different countries west and east, is at once the source of their riches, and of those rivers which conduct to the treasures which would be otherwise inaccessible in the eastern parts of the kingdoms of Benin, Congo, and Angola.
There are three remarkable appearances attending the inundation of the Nile; every morning in Abyssinia is clear, and the sun shines. About nine, a small cloud, not above four feet broad, appears in the east, whirling violently round as if upon an axis, but, arrived near the zenith, it first abates its motion, then loses its form, and extends itself greatly, and seems to call up vapours from all opposite quarters. These clouds having attained nearly the same height, rush against each other with great violence, and put me always in mind of Elisha foretelling rain on Mount Carmel[139]. The air, impelled before the heaviest mass, or swiftest mover, makes an impression of its own form in the collection of clouds opposite, and the moment it has taken possession of the space made to receive it, the most violent thunder possible to be conceived instantly follows, with rain; after some hours, the sky again clears, with a wind at north, and it is always disagreeably cold when the thermometer is below 63°.
The second thing remarkable is the variation of the thermometer; when the sun is in the southern tropic, 36° distant from the zenith of Gondar, it is seldom lower than 72°; but it falls to 60° and 59° when the sun is immediately vertical; so happily does the approach of rain compensate the heat of a too-scorching sun.
The third is, that remarkable stop in the extent of the rains northward, when the sun, that has conducted the vapours from the Line, and should seem, now more than ever, to be in possession of them, is here over-ruled suddenly, till, on its return to the zenith of Gerri, again it resumes the absolute command over the rain, and reconducts it to the Line to furnish distant deluges to the southward.
I cannot omit observing here the particular disposition of this peninsula of Africa; supposing a meridian line, drawn through the Cape of Good Hope, till it meets the Mediterranean where it bounds Egypt, and that this meridian has a portion of latitude that will comprehend all Abyssinia, Nubia, and Egypt below it, this section of the continent, from south to north, contains 64° divided equally by the equator, so that, from the Line to the southmost point of Africa, is 32°; and northward, to the edge of the Mediterranean, is 32° also: now, if on each side we set off 2°, these are the limits of the variable winds, and we have then 30° south, and 30° north, within which space, on both sides, the trade-winds are confined; set off again 16° from the 32°, that is, half the distance between the Cape of Good Hope and the Line, and 16° between the Line and the Mediterranean, and you have the limits of the tropical rains, 16° on each side of the equator: again, take half of 16°, which is 8°, and add it to the limit of the tropical rains, that is to 16°, and you have 24°, which is the situation of the tropics.—There is something very remarkable in this disposition.
CHAP. XVI.
Egypt not the Gift of the Nile—Ancient Opinion refuted—Modern Opinion contrary to Proof and Experience.
It is here we shall discuss a question often agitated, whether Egypt owed its existence to the Nile, and whether it was formerly an arm of the sea, but in process of time, being filled up by the quantity of mud which the Nile deposited in its inundation, it at length became firm land, above the surface of the waters? I believe this is the general opinion, as well of the books, as of the greatest part of travellers of the present age; it therefore merits examination, whether it is founded in fact and observation, or whether it is to be ranked among the old and ill supported traditions fancifully now again brought into fashion.