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store the equilibrium, and consequently produce the Khumseen wind, which for the same reason will precede the overflowing of the Nile, and begin first near the principal point of rarefaction. But as the sun approaches again towards the autumnal equinox, the earth to the northward becomes cool, the Khumseen ceases to blow, the river begins to fall, and the N.W. wind again com. mences, and continues to blow all the rest of the year.
It is true, as was before mentioned, that almost the same winds prevailed at the same season in the Gulf of Persia as in the north. ern part of the Arabian Gulf; but the eastern shore of the former being covered with both hills and forests, the Khumseen will nei. ther begin quite so soon in the Gulf of Persia as in Upper Egypt or Arabia, nor even continue to blow there with equal strength.
5. Sirocco. This peculiar wind, sometimes written Scirocco and Sciloco, proceeds in the south part of Italy and Sicily from the S.E. ; it blows occasionally with great force in the month of July, but sometimes commences faintly about the summer solstice.
This wind resembles the Khumseen, and the land wind in all tropical countries, not only in its appearance and effects, but likewise in the time of its commencement. It must be allowed, that it does not blow in the southern part of Europe without intermission for forty or fifty days, nor does it continue quite so long as those winds do in Asia and Africa, but it is extremely oppressive during the time it lasts, even to the Sicilians and Neapo. litans.
According to Mr. Brydone, the inhabitants of Palermo do not understand in what manner to guard against its effects so well as the natives of Hindustan; for the Sicilians content themselves with merely shutting their windows, and where there are no shutters they hang up a wet blanket instead of them, which must be very soon dried; but the wiser Indian puts a curtain of grass before the window or door, which he constantly wets on the side exposed to the wind, and thus by keeping up a constant evaporation, the air which passes into the room is rendered perfectly cool.
Mr. Kirwan observes, that the degree of cold, produced by evaporation when the air is warmer than the evaporating surface, is much greater than that which is produced when the evaporating surface is the warmer of the two. In this instance the air without is at 112 degrees even in the shade, and the evaporating surface, when frequently moistened, not more than 75 degrees. The most opulent and luxurious of the Hindoos make a sort of hut of per. fumed grass, which is kept constantly moistened, and exposed to the land wind, in which they live at a temperature of 60 degrees during the extreme heat of the day, and the continuance of the land wind.
The Sirocco has been supposed by some people to come from the opposite coast of Africa, and by others to be the effect of sul. phureous vapours from the earth; if, however, it came from the continent of Africa, it would be felt with great violence at sea, in the channel of Malta, and on the island itself ; but the Sirocco is not felt at this time on any part of the sea which separates Sicily from Africa, but, like the land wind in India, it is confined to the shores on both sides, whilst the sea wind on the southern shores of Europe, opposite to Africa, is, at this season, always cool and refreshing.
Mr. Bry done observes, that the Sirocco is felt with most vio. lence at Palermo, situated on the N.W. side of Sicily, and on the continent it is infinitely worse in the interior of the country near Naples, than in the southern part of Calabria: these circum. stances positively prove, that it is nothing more than the air, which acquires a considerable local degree of heat from the surface of the earth at the hottest season of the year, and in its ascent is impelled forward by the S. E. wind, so as to acquire additional heat as it proceeds towards the N.W. side of the island.
This progressive accumulation of heat from the land, during the Sirocco, may be ascertained by a person heating a piece of paper before the fire, and running the end of his finger along the heated paper ; at first it will appear only warm, but as the finger proceeds, and accumulates the heat of that part of the paper over which the finger passes, it will at length become so hot as to be paiósul.
6. Long-shore Wind. This is a kind of monsoon peculiar to the coast of the island of Ceylon, blowing from the southwest.
We have hence already sufficiently described it under the article Monsoons. Editor
7. Land and Sea Breezes. When the earth begins to be violently heated in the course of the day, the rarefied air ascends, and the cooler air from the sea comes in to supply its place; but the exhalations raised during the day are condensed in the cool of the evening, during the absence of the sun, and falling down in copious dews refresh the earth, when the sea becomes warmest, and the current of air, a few hours after sun-set, goes from the land to the sea, and produces what is called the land wind. It must be remembered, that these alternate land and sea breezes do not take place until some time after the change of each monsoon, when its strength begins to abate ; for at the commencement of either, the monsoon itself blows incessantly for a month or five weeks immediately on the coast, and continues, with triding deviations from the N.E. or S.W. according to the respective seasons. Nor do the land or sea breezes at any time extend above three or four leagues from the shore.
Mr. Clare, in his Treatise on the Motion of Fluids, shows the cause of these breezes by an easy and familiar experiment. “Take,"
a large dish, fill it with cold water, and into the middle of this put a water-plate filled with warm water : the first will represent the ocean, the latter an island, rarefying the air above it. Blow out a wax candle, and if the place be still, on apply. ing it successively to every side of the dish, the fuliginous particles of the spoke, being visible and very light, will be seen to move towards the dish, and rising over it, point out the course of the air from sea to land.
" Again, if the ambient water be warmed, and the dish filled with cold water, when the smoking wick of the candle be held over the centre of the plate, the contrary will happen, and show the course of the wind from land to sea."
Duriog the continuance of the land and sea breezes on the coasts of Coromandel and Malabar, both in the N. E. and S.W. mon. soons, the wind on shore seems regularly to follow the course of the sun, and passes very perceptibly round every point of the compass in twenty-four hours.
These winds blow constantly every year on the coast of Coro. mandel to the latter end of January, and continue during Fe. bruary and to the beginning of March, subject to very slight
variations; but as the sun approaches towards the vernal equinox, the winds again become variable for some days, as they were about the autumnal equinox, until his declination is upwards of seven degrees N. when the S.W. monsoon sets in, and often on the south part of the coast, with considerable violence. This change or reflux of air appears to be put in motion by the same means as that which comes from the opposite quarter; for as the sun's altitude increases daily in the northern hemisphere, the ex. tensive body of land in the N.E. part of Asia must become much hotter than the ocean, and consequently a considerable degree of rarefaction will be produced over that part of the continent, wbilst at the same season an immense body of cold air will come both from the Indian Ocean and the continent of Africa, in the southern hemisphere, to restore the equilibrium. The principal tracts of land of different temperatures on the two continents, bearing very nearly N.E. and S.W. of each other, will therefore become alter. nately the two opposite extreme points of rarefaction and conden. sation, and necessarily, according to this theory, be the immediate causes of the N.E. and S.W. monsoons.
Drawn op by Dr. Dobson, from Mr. Norris's Communications. Tue harmattan is a periodical wind, which blows from the inte. rior parts of Africa towards the Atlantic Ocean, and possesses such extraordinary properties, as to merit the attention of the naturalist, making a curious and important article in the history and theory of the winds.
On that part of the coast of Africa which lies between Cape Verd and Cape Lopez, an easterly wind prevails during December, January, and February, which by the Fantees, a nation on the Gold Coast, is called the harmattan. Cape Verd is in 15° N. lati. tude, and Cape Lopez in 1° S. latitude, and the coast between these two capes runs, in an oblique direction, nearly W. S. W. to E.S. E. forming a range of upwards of 2100 miles. At the Isles de Los, which are a little to the northward of Sierra Leone, and to the southward of Cape Verd, it blows from the E. S. E. on the Gold Coast from the N. E. and at Cape Lopez and the river Gabon, from the N. N. E. This wind is, by the French and Por. tugueze who frequent the Gold Coast, called the N. E. wind, the quarter from which it blows. The English, who sometimes bor. row words and phrases from the Fantee language, which is less. guttural and more harmonious than that of their neighbours, adopt the Fantee word harmattan. The harmattan comes on indiscrimi. nately, at any hour of the day, at any time of the tide, or at any period of the moon, and continues sometimes only a day or two, sometimes five or six days, and it has been known to last fifteen or sixteen days. There are generally three or four returns of it every season. It blows with a moderate force, not quite so strong as the sea breeze, which every day sets in during the fair season from the W., W.S. W., and S. W.; but somewhat stronger than the land wind at night from the N., and N. N. W.
1. A fog or haze is one of the peculiarities which always accom. panies the harmattan. The gloom occasioned by this fog is so great, as sometimes to make even near objects obscure. The English fort at Whydah stands about the midway between the French and Portuguese forts, and not quite a quarter of a mile from either, yet very often from it neither of the other forts can be discovered. The sun, concealed the greatest part of the day, appears only for a few hours about noon, and is then of a mild red, exciting no painful sensation on the eye. The particles which constitute the fog are deposited on the grass, the leaves of trees, and even on the skin of the negroes, so as to make them appear whitish. They do not flow far over the surface of the sea : at two or three miles distance from the shore the fog is not so thick as on the beach ; and at four or five leagues distance it is entirely lost, though the harmattan itself is plainly felt for ten or twelve leagues, and blows fresh enough to alter the course of the current.
2. Extreme dryness makes another extraordinary property of this wind. No dew falls during the continuance of the harmattan; nor is there the least appearance of moisture in the atmosphere. Vegetables of every kind are very much injured; all tender plants, and most of the productions of the garden, are destroyed; the grass withers, and becomes dry like hay; vigorous ever-greens likewise feel its pernicious influence; the branches of the lemon, orange, and lime trees droop, the leaves become flaccid, wither,