John Platts

CURIOSITIES RESPECTING WINDS, HURRICANES, &c.

Remarkable Winds in Egypt—Whirlwinds of Egypt—Tornado—Harmattan—Hurricane—Monsoons—Velocity of the Wind.

Remarkable Winds in Egypt.

Egypt is infested with the destructive blasts common to all warm countries which have deserts in their neighbourhood. These have been distinguished by various names, such as Poisonous winds, Hot winds of the desert, Samiel, the wind of Damascus, Camseen, and Simoom. In Egypt they are denominated “Winds of fifty days,” because they most commonly prevail during the fifty days preceding and following the equinox, though, should they blow constantly during one half of that time, an universal destruction would be the consequence. Of these, travellers have given various descriptions. M. Volney says, that the violence of their heat may be compared to that of a large oven at the moment of drawing out the bread. They always blow from the south, and are undoubtedly owing to the motion of the atmosphere over such vast tracts of hot sand, which cannot be supplied with a sufficient quantity of moisture. When they begin to blow, the sky loses its usual serenity, and assumes a dark, heavy, and alarming aspect, the sun laying aside his usual splendour, and becoming of a violet colour. This terrific appearance seems not to be occasioned by any real haze or cloud in the atmosphere at that time, but solely by the vast quantity of fine sand carried along by those winds, and which is so excessively subtile that it penetrates every where. The motion of this wind is always rapid, but its heat is not intolerable till it has continued for some time. Its pernicious qualities are evidently occasioned by its excessive aridity; for it dries and shrivels up the skin, and, by affecting the lungs in a similar manner, soon produces suffocation and death. The danger is greatest to those of a plethoric habit, or who have been exhausted by fatigue; and putrefaction very soon takes place in the bodies of such as are destroyed by it. Its extreme dryness is such, that water sprinkled on the floor evaporates in a few minutes; all the plants are withered and stripped of their leaves, and a fever is instantly produced in the human species by the suppression of perspiration. It usually lasts three days, but is altogether insupportable if it continue beyond that time.

The danger is greatest when the wind blows in squalls, and to travellers who happen to be exposed to its fury without any shelter. The best method, in this case, is to stop the nose and mouth with a handkerchief: camels, by a natural instinct, bury their noses in the sand, and keep them there till the squall is over. The inhabitants, who have an opportunity of retiring to their houses, instantly shut themselves up in them, or go into pits made in the earth, till the destructive blast is over.

The description of a blast of this kind, which overtook Mr. Bruce, in the desert of Nubia, is still more terrible.—The sun was now obscured by them,[21] and the transmission of his rays gave them a dreadful appearance, resembling pillars of fire. This was pronounced by the guide to be a sign of the approaching simoom, or hot wind; and he directed, that when it came, the people should fall upon their faces, and keep their mouths on the sand, to avoid drawing in this pernicious blast with their breath. On his calling out that the simoon was coming, Mr. Bruce turned for a moment to the quarter from whence it came, which was the south-east. It appeared like a haze or fog of a purple colour, but less bright than the purple part of the rainbow; seemingly about twenty yards in breadth, and about twelve feet high from the ground. It moved with such rapidity, that before he could turn about and fall down, he felt the vehement heat of its current upon his face; and even after it passed over, which was very quickly, the air which followed was of such a heat as to threaten suffocation. Mr. Bruce had unfortunately inspired some part of the pernicious blast; by which means he almost entirely lost his voice, and became subject to an asthmatic complaint, from which he did not get free for two years.

The same phenomenon occurred twice over on their journey through this desert. The second time it came from the south a little to the east, but it seemed to have a shade of blue along with the purple, and its edges were less perfectly defined, resembling rather a thin smoke, and having about a yard in the middle tinged with blue and purple.

The third time, it was preceded by an appearance of sandy pillars, more magnificent than any they had yet observed; the sun shining through them in such a manner as to give those which were nearest a resemblance of being spangled with stars of gold. The simoom which followed had the same blue and purple appearance as before, and was followed by a most suffocating wind for two hours, which reduced our travellers to the lowest degree of weakness and despondency.

It was remarkable, that this wind always came from the south-east, while the sandy pillars, which prognosticated its approach, seemed to keep to the westward, and to occupy the vast circular space inclosed by the Nile to the west of their route, going round by Chaigie towards Dongola. The heaps of sand left by them when they fell, or raised by the whirlwinds which carried them up, were twelve or thirteen feet high, exactly conical, tapering to a fine point, and their bases well proportioned.

The following account of the Whirlwinds of Egypt, is from Belzoni’s Narrative:—“A strong wind which arose this day leads me to mention some particulars of the phenomena that often happen in Egypt. The first I shall notice is the whirlwinds, which occur all the year round, but especially at the time of the camseen wind, which begins in April, and lasts fifty days. Hence the name of camseen, which in Arabic signifies fifty. It generally blows from the south-west, and lasts four, five, or six days without varying, so very strong that it raises the sands to a great height, forming a general cloud, so thick that it is impossible to keep the eyes open, if not under cover. It is troublesome, even to the Arabs; it forces the sand into the houses through every cranny, and fills every thing with it. The caravans cannot proceed in the deserts; the boats cannot continue their voyages; and travellers are obliged to eat sand, in spite of their teeth. The whole is like a chaos. Often a quantity of sand and small stones gradually ascends to a great height, and forms a column of sixty or seventy feet in diameter, and so thick, that were it steady on one spot, it would appear a solid mass. This not only revolves within its own circumference, but runs in a circular direction over a great space of ground, sometimes maintaining itself in motion for half an hour, and wherever it falls it accumulates a small hill of sand. God help the poor traveller who is caught under it!”

We shall now describe a Tornado.—This is a sudden and vehement gust of wind from all points of the compass, and frequent on the coast of Guinea. A tornado seems to partake much of the nature of a whirlwind, or perhaps of a water-spout, but is more violent in its effects. It commences very suddenly: several clouds being previously drawn together, a spout of wind, proceeding from them, strikes the ground, in a round spot of a few rods or perches in diameter, and proceeds thus half a mile or a mile. The proneness of its descent makes it rebound from the earth, throwing such things as are moveable before it, sideways, or in a lateral direction from it. A vapour, mist, or rain, descends with it, by which the path of it is marked with wet.

The following is a description of one which happened a few years since at Leicester, about fifty miles from Boston, in New England: it happened in July, on a hot day, about four o’clock in the afternoon. A few clouds having gathered westward, and coming over-head, a sudden motion of their running together in a point, being observed, immediately a spout of wind struck the west end of a house, and instantly carried it away, with a negro man in it, who was afterwards found dead in its path. Two men and a woman, by the breach of the floor, fell into the cellar; and one man was driven forcibly up into the chimney corner. These were preserved, though much bruised; they were wet with a vapour or mist, as were the remains of the floor, and the whole path of the spout. This wind raised boards, timbers, &c. A joist was found on one end, driven nearly three feet into the ground. The spout probably took it in its elevated state, and drove it forcibly down. The tornado moved with the celerity of a moderate wind, and declined in strength till it entirely ceased.

Harmattan.—This is a name given to a singular wind, which blows periodically from the interior parts of Africa, towards the Atlantic ocean. It prevails in December, January, and February, and is generally accompanied by a fog or haze, that conceals the sun for whole days together. Extreme dryness is the characteristic of this wind: no dew falls during its continuance, which is sometimes for a fortnight or more. The whole vegetable creation is withered, and the grass becomes at once like hay. The natives take the opportunity which this wind gives them, of clearing the land, by setting fire to trees and plants in this their exhausted state. The dryness is so extreme, that household furniture is damaged, and the wainscot of the rooms flies to pieces. The human body is also affected by it, so as to cause the skin to peel off; but in other respects it is deemed salutary to the constitution, by stopping the progress of infection, and curing almost all cutaneous diseases.

We now proceed to some curious particulars, under the term Hurricane.—This is indeed a general name for any violent storm of wind, but is peculiarly applied to those storms which happen in the warmer climates, and which greatly exceed the most violent ones known in this country. Dr. Mosely, in his Treatise on Tropical Diseases, observes, that the ruin and desolation accompanying a hurricane can scarcely be described. Like fire, its resistless force consumes every thing in its track, in the most terrible and rapid manner. It is generally preceded by an awful stillness of the elements, and a closeness and mistiness in the atmosphere, which makes the sun appear red, and the stars larger. But a dreadful reverse succeeds: the sky is suddenly overcast and wild; the sea rises at once from a profound calm into mountains; the wind rages and roars like the noise of cannon; the rain descends in a deluge; a dismal obscurity envelops the earth with darkness; and the superior regions appear rent with lightning and thunder. The earth on these occasions often does, and always seems to tremble; whilst terror and consternation distract all nature: birds are carried from the woods into the ocean; and those whose element is the sea, seek for refuge on land; the frightened animals in the field assemble together, and are almost suffocated by the impetuosity of the wind in searching for shelter, which, when found, is but the prelude to destruction. The roofs of houses are carried to vast distances from their walls, which are beat to the ground, burying their inhabitants under them. Large trees are torn up by the roots, and huge branches shivered off, and driven through the air in every direction with immense velocity. Every tree and shrub that withstands the shock is stripped of its boughs and foliage; plants and grass are laid flat on the earth; and luxuriant spring is changed in a moment to dreary winter. This direful tragedy ended, (when it happens in a town,) the devastation is surveyed with accumulated horror: the harbour is covered with wrecks of boats and vessels; and the shore has not a vestige of its former state remaining. Mounds of rubbish and rafters in one place; heaps of earth and trunks of trees in another; deep gullies from torrents of water; and the dead and dying bodies of men, women, and children, half buried, and scattered about, where streets stood but an hour before,—present the miserable survivors with the shocking conclusion of a spectacle, to be followed by famine, and, when accompanied by an earthquake, by mortal diseases.

Philosophers are now inclined to attribute these terrible phenomena to electricity, though the manner in which it acts in this case is by no means known. It seems probable, indeed, that not only hurricanes, but even the most gentle gales of wind, are produced by the action of the electric fluid.

In the next place we shall treat of Monsoons, or Trade-Winds.

“Trade-winds, observing well their stated course,
To human good employ their pow’rful force;
The loaded ships across the ocean fann’d
By steady gales, spread commerce through the land:
These you observe—but have you no desire
The hidden spring of such effects t’inquire?
Or, when contending winds around you blow,
Do you ne’er wish the cause of them to know?”

Monsoons are those winds which blow six months constantly the same way, and the contrary way the other six months.

Mr. Olinthus Gregory observes, that “though the winds in a temperate zone of the earth are very inconstant and changeable, yet this is not the case in every part of the terrestrial globe; for in the torrid zone, and some other parts, the winds are generally very uniform and constant in their direction, as will appear from the following facts relative thereto:—

“1. Over the Atlantic, and Pacific oceans, particularly between thirty degrees of north and thirty degrees of south latitude, the trade-winds, as they are called, blow uniformly from east to west, all the year round, with a small variation in the different seasons.

“2. When the sun is on the equator, the trade-winds, in sailing northward, veer more and more from the east towards the north; so that about their limit they become nearly north-east; and vice versa in sailing southward, they become at last nearly south-east. 3. When the sun is near the tropic of Cancer, the trade-winds north of the equator become more nearly east than at other times, and those south of the equator more nearly south; and vice versa, when the sun is near the tropic of Capricorn. 4. The trade-winds are not due east upon the equator, but about four degrees to the north of it.

“To account for these facts relative to the winds, is a most curious and important, though mysterious, inquiry; having employed the pens of several very eminent philosophers: but amongst all the explanations I have seen, there is none in my opinion more agreeable to nature than one given by Mr. John Dalton, of Manchester, in his “Meteorological Observations and Essays.” The method of reasoning applied to the subject in that work, I shall here make use of.

“The inequality of heat in the different climates and places, and the earth’s rotation on its axis, appears to be the principal causes of all winds, regular and irregular. It may be observed, that whenever the heat is greatest, there the air will ascend, and a supply of colder air will be received from the neighbouring parts: it will be willingly allowed, that the heat is at all times greatest in the torrid zone, and decreases gradually in proceeding northward or southward; also that the poles may at all times be considered as the centres of cold. Hence it reasonably follows, that abstracting from accidental circumstances, there will be a constant ascent of air over the torrid zone, which air will afterwards fall northward and southward, whilst the colder air below is determined by a continual impulse towards the equator.

“When the effects of the earth’s rotation are taken into consideration, our reasoning must be as follows: the air over any part of the earth’s surface, when apparently at rest, or calm, will have the same rotatory velocity as that part; but if a quantity of air in the northern hemisphere receive an impulse in the direction of the meridian, either northward or southward, its rotatory velocity will be greater in the former case, and less in the latter, than that of the air into which it moves; consequently, if it move northward, it will have a greater velocity eastward than the air, or surface of the earth over which it moves, and will therefore become a south-west wind, or a wind between the south and west; and, vice versa, if it move southward, it becomes a north-east wind. From similar considerations it will appear, that in the southern hemisphere the winds will be north-west and south-east respectively.

“The trade-winds may therefore be explained thus: The two general masses of air proceeding from both hemispheres towards the equator, as they advance are constantly deflected more and more towards the east, by reason of the earth’s rotation; that from the southern hemisphere, originally a south wind, is made to veer more and more towards the east; in like manner, that from the northern hemisphere is made to change its directions from the north towards the east: these two masses meeting near the equator, their velocities south and north destroy each other, and they proceed afterwards with their common velocity from east to west round the torrid zone, excepting the irregularities produced by the continents. The equator is not in reality the place of concourse, but the northern parallel of four degrees; because the centre of heat is thereabouts, the sun being longer on the north side of the equator, than on the south side. Moreover, when the sun is near one of the tropics, the centre of heat upon the earth’s surface is then nearer that tropic than usual, and therefore the winds about the tropic are more nearly east at that time, and those about the other tropic more nearly north and south.

“If all the terrestrial globe were covered with water, or if the variations of the earth’s surface in heat were regular and constant, so that the heat was the same in every part of the same parallel of latitude, the winds would then be very nearly regular also: but this is not the case; for we find the irregularities of heat, arising from the interspersion of land and sea, are such, that though all the parts of the atmosphere in some measure conspire to produce regular winds about the torrid zone, yet very striking irregularities are often found to take place. A remarkable instance we have in monsoons, which are winds that in the Indian ocean, &c. blow for six months together one way, and the next six months the contrary way: these, with sea and land breezes, do not seem easily to be accounted for on any other principle than that of rarefaction.

“Perhaps some persons may be led to suppose, that the winds in the northern temperate zone should be between the north and east towards the poles, and between the south and west nearer the equator, almost as regular as the trade-winds: but when the change of seasons, the different capacities of land and water for heat, the interference and opposition of the two general currents, be considered, it might be concluded almost next to impossible that the winds in the temperate zone should exhibit any thing like regularity: however, notwithstanding this, observations sufficiently evince, that the winds therein are, for the most part, in the direction of one of the general currents; namely, somewhere between the south and west, or more commonly between the north and east; and that winds in other directions happen only as accidental varieties, chiefly in unsettled weather.

FALLING OR SHOOTING STARS.—Page 681.

The engraving represents an extraordinary shower of these remarkable meteors, which took
place at the Falls of Niagara. The view comprises the entire falls, with Goat Island in the centre.

COMMENCEMENT OF THE SOUTH-WEST MONSOON IN INDIA.—Page 515.

“We may have frequently taken notice, that several winds, particularly stormy ones, are attended with a cloudy sky; to this it may be added, that we have more winds than usually occur in rather less latitudes, where the atmosphere is generally more serene: these considered, make it exceedingly probable, that the aqueous vapours which are sustained by the air, from whence come clouds and rains, may be one great cause of irregular winds. It has been determined, from very accurate experiments, that one inch of water when evaporated will fill more than 2000 inches of space: hence it appears that the water which falls in drops of rain, &c. occupied more than 2000 times the space when it floated in the atmosphere in vapours; the condensation thereof must therefore occasion vacua of such a nature, as will cause winds of different kinds and degrees, according to the deficiency which is to be supplied.

“The economy of winds, an illustration of which has been here attempted, is admirably adapted to the various purposes of nature, and to the general intercourse of mankind:—if the earth had been fixed, and the sun had revolved about it, the air over the torrid zone, and particularly about the equator, would have been almost always stagnant; and in the other zones the winds would have had little variation either in direction or strength; in this case navigation would have been greatly impeded, and a communication between the two hemispheres by sea, rendered impracticable. On the present system of things, however, the irregularity of winds is of the happiest consequence, by being subservient to navigation: and a general circulation of air constantly takes place between the eastern and western hemispheres, as well as between the polar and equatorial regions; by reason of which, that diffusion and intermixture of the different aËrial fluids, so necessary for the life, health, and prosperity of the animal and vegetable kingdoms, is accomplished:—such is the transcendent wisdom and providential care of the beneficent Father of all!”

The following interesting description of the South-west Monsoon in India, is taken from Elphinstone’s Account of Cabul.—The most remarkable rainy season, is that called in India the South-west Monsoon. It extends from Africa to the Malay Peninsula, and deluges all the intermediate countries within certain lines of latitude, for four months in the year. In the south of India, this monsoon commences about the beginning of June, but it gets later as we advance towards the north. Its approach is announced by vast masses of clouds that rise from the Indian ocean, and advance towards the north-east, gathering and thickening as they approach the land. After some threatening days, the sky assumes a troubled appearance in the evenings, and the monsoon in general sets in during the night. It is attended with such a thunder-storm as can scarcely be imagined by those who have only seen that phenomenon in a temperate climate. It generally begins with violent blasts of wind, which are succeeded by floods of rain. For some hours, lightning is seen almost without intermission; sometimes it only illuminates the sky, and shews the clouds near the horizon; at others, it discovers the distant hills, and again leaves all in darkness; when in an instant it re-appears in vivid and successive flashes, and exhibits the nearest objects in all the brightness of day. During all this time the distant thunder never ceases to roll, and is only silenced by some nearer peal, which bursts on the ear with such a sudden and tremendous crash, as can scarcely fail to strike the most insensible heart with awe. At length the thunder ceases, and nothing is heard but the continued pouring of the rain, and the rushing of the rising streams. The next day presents a gloomy spectacle: the rain still descends in torrents, and scarcely allows a view of the blackened fields; the rivers are swollen and discoloured, and sweep down along with them the hedges, the huts, and the remains of the cultivation, which was carried on during the dry season, into their beds.

This lasts for some days, after which the sky clears, and discovers the face of nature, changed as if by enchantment. Before the storm, the fields were parched up, and, except in the beds of the rivers, scarce a blade of vegetation was to be seen; the clearness of the sky was not interrupted by a single cloud, but the atmosphere was loaded with dust, which was sufficient to render distant objects dim, as in a mist, and to make the sun appear dull and discoloured, till he attained a considerable elevation: a parching wind blew like a blast from a furnace, and heated wood, iron, and every other solid material, even in the shade; and immediately before the monsoon, this wind had been succeeded by still more sultry calms. But when the first violence of the storm is over, the whole earth is covered with a sudden but luxuriant verdure: the rivers are full and tranquil, the air is pure and delicious; and the sky is varied, and embellished with clouds. The effect of the change is visible on all the animal creation, and can only be imagined in Europe, by supposing the depth of a dreary winter to start at once into all the freshness and brilliancy of spring. From this time the rain falls at intervals for about a month, when it comes on again with great violence, and in July the rains are at their height; during the third month, they rather diminish, but are still heavy; and in September they gradually abate, and are often entirely suspended till near the end of the month, when they depart amidst thunders and tempests, as they came.

The following Table, which gives some particulars respecting the Velocity of the Wind, was calculated by Mr. John Smeaton, the celebrated engineer, and is founded on a correct series of practical observations:—

We conclude this chapter with a poetical enumeration of the benefits arising from the wind:—

“Of what important use to human kind,
To what great ends subservient, is the wind!
Where’er the aËrial active vapour flies,
It drives the clouds, and ventilates the skies;
Sweeps from the earth infection’s noxious train,
And swells to wholesome rage the sluggish main.
For should the sea unagitated stand,
Death, with huge strides, would desolate the land;
The scorching sun, with unpropitious beam,
Would give to grief an everlasting theme;
And baneful vapours, lurking in the veins,
Would fiercely burn with unabating pains.
Nor thus alone air purities the seas,
O’er torrid climes it pours the healthful breeze:
Climes where the sun direct flings scorching day,
Feel cooling air his sultry rage allay;
Unceasing goodness, with unceasing skill,
Educing certain good from seeming ill.
His guardian care extends o’er ev’ry shore,
And blends his favours with what men deplore;
The sable nations hence, and burning skies,
See luscious fruits in varying beauty rise;
Spontaneous Nature laugh at culture’s toil,
And rich luxuriance bless the grateful soil.”