Abbildungen der Seite
PDF
EPUB

and, if the harmattan continues to blow for ten or twelve days, are so parched as to be easily rubbed to dust between the fingers : the fruit of these trees, deprived of its nourishment, and stinted in its growth, only appears to ripen, for it becomes yellow and dry, without acquiring half the usual size. The natives take this opportunity, of the extreme dryness of the grass and young trees, to set fire to them, especially near their roads, not only to keep the roads open to travellers, but to destroy the shelter which long grass, and thickets of young trees, would afford to skulking par. ties of their enemies. A fire thus lighted flies with such rapidity as to endanger those who travel,: in that situation a common method of escape is, on discovering a fire to windward, to set the grass on fire to leeward, and then follow your own fire. There are other extraordinary effects produced by the extreme dryness of the harmattan. The covers of books, even closely shut up in a trunk, and lying among clothes, are bent as if they had been exposed to the fire. Household furniture is also much damaged: the pannels of doors and of wainscot split, and any veneered work flies to pieces. The joints of a well-laid floor of seasoned wood opened sufficiently to lay one's finger in them; but become as close as before on the ceasing of the harmattan. The seams also in the sides and decks of ships are much injured, and the ships become very leaky, though the planks are two or three inches in thickness. Iron-bound casks require the hoops to be frequently driven tighter; and a cask of rum or brandy, with wooden hoops, can scarcely be preserved; for, unless a person attends to keep it moistened, the hoops fly off.

The parching effects of this wind are likewise evident on the external parts of the body. The eyes, nostrils, lips, and palate, are rendered dry and uneasy, and drink is often required, not so much to quench thirst, as to remove a painful aridity in the fauces. The lips and nose become sore, and even chapped; and though the air be cool, yet there is a troublesome sensation of prickling heat op the skin. If the harmattan continues four or five days, the scarf skin peels off, first from the hands and face, and afterwards from the other parts of the body, if it continues a day or two longer. Mr. Norris, who frequently visited the coast of Africa, observed, that when sweat was excited by excercise on those parts which were covered by his clothes from the weather, it was pecu. liarly acrid, and tasted, on applying his tongue to his arm, some. thing like spirit of hart's.horn diluted with water.

As the state of salt of tartar placed in the open air, and the quantity evaporated from a giren surface of water, are obvious proofs of the comparative moisture or dryness of the atmosphere, Mr. Norris put the harmattan to each of these tests; and particu. larly to moisten salt of tartar ad deliquium, and exposed it to the night air during the time that the harmattan was blowing. The following is the account of the result of these experiments. Sale of tartar will not only remain dry during the night as well as in the day, but when liquefied so as to run on a tile, and exposed to the harmattan, becomes perfectly dry in two or three hours; and, exposed in like manner to the night air, will be dry before morning.

It appears, from experiments made by Mr. Norris, that if the evaporation of the whole year be supposed to go on in the same proportion with what occurred during a short and rery moderate return of the barmattan, the annual harmattan evaporation would be 133 inches; and if the calculation was made in proportion to the evaportion which occurs during a longer visit from the harmattan, and a more forcible breeze, the annual harmattan evaporation would be much more considerable. If the annual evaporation be in like manner calculated, in proportion to the evaporation which took place subsequent to and preceding the harmattan, the annual evaporation at Whydah, on the Gold Coast, would be 61 inches, and he had found the annual evaporation at Liverpool to be 36 inches. These three therefore are in the following proportion; harmattan 133 inches, Whydah 64 inches, and Liverpool 36 inches.

3. Salubrity forms a third peculiarity of the harmattan. Though this wind is so very prejudicial to vegetable life, and occasions such disagreeable parching effects on the human species, yet it is highly conducive to health. Those labouring under fluxes and intermit. ting fevers generally recover in an harmattan. Those weakened by fevers, and sinking under evacuations for the cure of them, particularly bleeding, which is often injudiciously repeated, have their lives saved, and vigour restored, in spite of the doctor. It stops the progress of epidemics: the small.pox, remittent fevers, &c. not only disappear, but those labouring under these diseases,

when an harmattan comes on, are almost certain of a speedy re. covery. Infection appears not then to be easily communicated even by art. In the year 1770 there were on board the Unity, at Whydah, above 900 slaves; the small-pox broke out among them, and it was determined to inoculate; those who were inoculated before the harmattan came on, got very well through the disease. About 70 weie inoculated a day or two after the harmattan set id; but not one of them had either sickness or eruption. It was imagined, that the infection was efíectually dispersed, and the ship clear of the disorder; but in a very few weeks it began to appear among these 70. About 50 of them were inoculated the second time; the others had the disease in the natural way: an harmattan came on, and they all recovered, except one girl, who had an ugly ulcer on the inoculated part, and died some time afterwards of a locked-jaw. Mr. Norris dissents from Dr. Lind, who speaks of the harmattan as “ fatal and malignant; that its noxious va. pours are destructive to blacks as well as whites; and that the mortality which it occasions is in proportion to the density and duration of the fog.” The baneful effects here pointed out pro. ceed from the periodical rains which fall in March, April, &c. and which are ushered in by the tornados, or strong gusts of wiod from the N. E. and E. N. E. accompanied with violent thunder and lightning, and very heavy showers. The earth, drenched by these showers and acted on with an intense solar heat as soon as the storm is over, sends forth such noisome vapours as strike the nostrils with a most offensive stench, and occasion bilious vomit. ings, fluxes, and putrid fevers. Besides these vapours, which are annual, there appears to be a collection of still more pestiferous matter, confined for a longer time, and issuing from the earth after an interval of five, six, or seven years. There may indeed be instances in which the harmattan comes loaded with the effluvia of a putrid marsh; and if there are any such situations, the nature of the wind may be so changed as to become even noxious.

It appears that, except a few rivers and some lakes, the country about and beyond Whydah is covered for 400 miles back with verdure, open plains of grass, clumps of trees, and some woods of no considerable extent. The surface is sandy, and below that a rich reddish earth; it rises with a gentle ascent for 150 miles from the sea before there is the appearance of a bill, without affording a stone of the size of a walnut. Beyond these hills there is no account of any great ranges of mountains. With respect to the origin of this wind, Mr. Norris says, “the harmattan, according to Dr. Lind, arises from the conflux of several rivers about Benin ; but when I was on a visit to the king of Dahomey, 120 miles north, or inland from the fort at Whydah, I there felt the har. mattan blowing from the N. E. stronger than I have at any other time, though Benin then bore from me S. E." On this head Mr. Norris makes the following conjecture : " The intersection of three lines, viz. an east line drawn from Cape Verd, a north-east one from the centre of the Gold Coast, and a north line from Cape Lopez, whould point out a probable source of this extraordinary wind.” Three lines, drawn according to the direction of Mr. Norris, towards the points of the compass from which the har. mattan blows on Cape Verd, the Gold Coast, and Cape Lopez, converge to a part of Africa about the 15th degree of north lati. tude, and the 25th degree of east longitude, which is that part of Africa where, according to Ptolemy, the mountains of Caphas are situated. From these mountains, according to the same authority, the river Daradus arose, supposed by some to be now the river Senegal. It may be conjectured, that the disagreeable Levant wind of the Mediterranean proceeds from the same part of the continent of Africa ; for it prevails during the same season of the year, and may derive its qualities from the surface over which it passes,

The Fantees have given the name of harmattan to one of the eight seasons into which they divide their year. Aherramantah, or the harmattan, extends from the 1st December to the middle of February, about ten weeks. Quakorah, a wind up the coast, from S. S. W. to S.S. E. from the middle of February to the first week in March, about three weeks. Pempina, or tornado season, part of March, all April, and the greatest part of May, about twelve weeks. Abrenama, or the old man's and woman's chil. dren, that is, the Pleiades, the rainy season, the latter end of May, all June, and to about the 20th of July, eight weeks. Atukogan, or five stars, that is, Orion, high wiod and squally, the rains very heavy, to the middle of August, three weeks. Worrobakorou, or one star, the ceasing of the rains, about three weeks. Mawur. rah, the name of a certain star; close foggy weather, and no breeze, the first three weeks in September. Boutch, no land breeze in this season, the wind blows fresh down the coast, about six weeks. Autiophi, or the croziers; tornados and southerly wind, with some rain, generally called the latter rains, about four weeks, to the beginning of December, when the Aherramantah season again commences.

[Phil. Trans. Abr. 1781.

SECTION V.

Topical or Toral winds.

1. Samiel or Sumyel. The Sumyel, strictly speaking, should rather be considered as an Asiatic than an African wind; for although it is said to prevail to the eastward of Belud-ul-Gerid, and the Libyan Desert, it is felt with its greatest force on the great Desert of Arabia, and sometimes in countries bordering on the Gulf of Persia. On the derivation of the term authors are very much divided, but they all agree respecting its appearance and effects.

Mr. Volney seems to consider the Sumyel the same as the Khumseen, and he calls it the Shamyala, supposing the name to be derived from Sham, the country of Syria.

But I am rather disposed to adopt the derivation of Sir J. Chardin, Yel, Turkish, wind, and Sum, Arabic, poison, particularly as the Persians likewise call it Bad Samoum, which is precisely the same signification, poisonous wind. Nor should this wind be confounded with the Khumseen and Scirocco, which proceed from the same cause, and are exactly the same in appearance and dura. tion as the land wind of India. The two latter blow for seven or eight weeks, at the latter end of May, all June, and part of July, in almost all inland countries situated within and near the northern tropic; but the natives of those countries in general do not esteem these hot winds particularly unwholesome, whereas the Sumyel blows only occasionally, and is a transient pestiferous current of air containing a deleterious gas, that in its passage always proves fatal both to man and beast. It is true, that the Sumyel in one respect resembles the Khumseen, for it generally appears during the hottest time of the year, but the gusts of it are merely local and instantaneous.

« ZurückWeiter »