These sands are so fine, and driven with such | which was, perhaps, the pestilence of the anviolence, that they penetrate everywhere, even into chests, be they shut never so closely. If these winds happen to continue for any length of time, they produce epidemic diseases, and are often followed by a great mortality. It is also found to rain but very seldom in that country: however, the want of showers is richly compensated by the copiousness of their dews, which greatly tend to promote vegetation. In Persia, the winter begins in November, and continues till March. The cold at that time is intense enough to congeal the water; and snow falls in abundance upon their mountains. During the months of March and April, winds arise, that blow with great force, and seem to usher in the heats of summer. These return again, in autumn, with some violence; without, however, producing any dreadful effects. But during their summer, all along the coasts of the Persian gulf, a very dangerous wind prevails, which the natives call the Sameyel, still more dreadful and burning than that of Egypt, and attended with instant and fatal effects. This terrible blast, kind of light and colours which I had not before seen. The sun, without being concealed, had lost its rays; it had even less lustre to the eye than the moon, and gave a pale light without shade; the waters of the Nile no longer reflected its rays, but appeared in agitation; everything had changed its usual aspect; it was now the flat shore that seemed luminous, and the air dull and opaque; the yellow horizon showed the trees on its surface of a dirty blue; flocks of birds were flying off before the cloud: and frighted animals ran loose in the country, followed by the inhabitants, who vainly attempted to collect them together again. We could now easily conceive the dreadful situation of those who are surprised with such a phenomenon of nature, when crossing the exposed and naked deserts; where, as it stands upon record, many thousands have been overwhelmed and lost in the shoals of sand raised by the Kainsin winds. The next day an astonishing mass of dust, attended with similar appearances, travelled along the desert of Libya: it followed the chain of the mountains, and when we flattered ourselves that we were entirely rid of this pestilence, the west wind brought it back, and once more overwhelmed us with this scorching torrent; the light of the sun could pierce with difficulty through this dense vapour; all the elements appeared to be in disorder; rain was mixed with whirlwinds of fire, wind, and dust, and, in this time of confusion, the trees, and all the other productions of nature, seemed to be again plunged in the horrors of chaos. If the desert of Libya had sent us these clouds of dust, those on the east, on the contrary, had been inundated with water; for the merchants who came from the borders of the Red sea, told us, that in the valleys they had the water up to the middle of their legs. When this destructive scourge sets in from the desert, the inundation of sand overwhelms the country, changes its fertility to barrenness, drives the labourer from his house, whose walls it covers up, and leaves no other mark of vegetable life but the tops of a few palm-trees, which adds still more to the dreary aspect of destruction. Thus the desert is constantly encroaching on the fertile land; and, were the water of the Nile to discontinue its inundations, the whole vale of Egypt would eventually become a desert or bed of sand."-ED. cients, instantly kills all those that it involves in its passage. What its malignity consists in, none can tell, as none have ever survived its effects, to give information.10 It frequently, as I am told, assumes a visible form, and darts, in a kind of bluish vapour, along the surface of the country. The natives, not only of Persia, but of Arabia, talk of its effects with terror; and their poets have not failed to heighten them with the assistance of imagination. They have described it as under the conduct of a minister of vengeance, who governs its terrors, and raises or depresses it as he thinks proper. These deadly winds are also known along the coasts of India, at Negapatam, Masulipatam, and Petapoli. But, luckily for mankind, the shortness of their duration diminishes the injuries that might ensue from their malignity. 11 The Cape of Good Hope, as well as many islands in the West Indies, are famous for their hurricanes, and that extraordinary kind of cloud which is said to produce them. This cloud, which is the forerunner of an approaching hurricane, appears, when first seen, like a small black spot, on the verge of the horizon; and is called by sailors the bull's eye, from being seen so minute at a vast distance.12 All this time a perfect calm reigns over the sea and land, while the cloud grows gradually broader as it approaches. At length, coming to the place where its fury is to fall, it invests the whole horizon with darkness. During all the time of its approach, a hollow murmur is heard in the cavities of the mountains; and beasts and animals, sensible of its approach, are seen running over the fields, to seek for shelter. Nothing can be more terrible than its violence when it begins. The houses in those countries, which are made of timber, the better to resist its fury, bend to the blast like osiers, and again recover their rectitude. The sun, which but a moment before blazed with meridian splendour, is totally shut out; and a midnight darkness prevails, except that the air is incessantly illuminated with gleams of lightning, by which one can easily see to read. The rain falls, at the same time, in torrents; and its descent has been resembled to what pours from the spouts of our houses after a violent shower. These hurricanes are not less offensive to the sense of smelling also, and never come without leaving the most noisome stench behind them. 10 It is said of this wind, that if it happens to meet with a shower of rain in its course, and blows across it, it is at once deprived of its noxious quality, and becomes mild and innocent. It is also said, that it was never known to pass the walls of a city. Its fatal effects probably proceed from a certain portion of extremely putrid vapours with which it is charged, by blowing over some very putrid and stagrant lake. 11 Herbelot, Bibliotheque Oriental. 12 The water-spout or syphon is a no less dangerous phenomenon. An account of it will be found in the succeeding chapter. If the seamen also lay by their wet clothes for | All this is terrible; but there is a tempest, twenty-four hours, they are all found swarming with little white maggots, that were brought with the hurricane. Our first mariners, when they visited these regions, were ignorant of its effects, and the signs of its approach; their ships, therefore, were dashed to the bottom at the first onset; and numberless were the wrecks which the hurricane occasioned. But at present, being forewarned of its approach, they strip their masts of all their sails, and thus patiently abide its fury. These hurricanes are common in all the tropical climates. On the coasts of Guinea they have frequently three or four in a day, that thus shut out the heavens for a little space; and, when past, leave all again in former splendour. They chiefly prevail, on that coast, in the intervals of the trade-winds; the approach of which clears the air of its meteors, and gives these mortal showers that little degree of wholesomeness which they possess. They chiefly obtain there during the months of April and May; they are known, at Loango, from January to April; on the opposite coast of Africa, the hurricane season begins in May; and, in general, whenever a trade-wind begins to cease, these irregular tempests are found to exert their fury.13 known in those climates, more formidable than any we have hitherto been describing, which is called, by the Spaniards, a Tornado. As the former was seen arriving from one part of the heavens, and making a line of destruction; so the winds in this seem to blow from every quarter, and settle upon one destined place, with such fury that nothing can resist their vehemence. When they have all met, in their central spot, then the whirlwind begins with circular rapidity. The sphere every moment widens, as it continues to turn, and catches every object that lies within its attraction. This also, like the former, is preceded by a flattering calm; the air is everywhere hushed, and the sea is as smooth as polished glass: however, as its effects are more dreadful than those of the ordinary hurricane, the mariner tries all the power of his skill to avoid it; which, if he fails of doing, there is the greatest danger of his going to the bottom. All along the coasts of Guinea, beginning about two degrees north of the Line, and so downward, lengthwise, for about a thousand miles, and as many broad, the ocean is unnavigable, on account of these tornadoes. In this torpid region there reigns unceasing tornadoes, or continual calms; among which, what+ ever ship is so unhappy as to fall, is totally deprived of all power of escaping. In this dreadful repose of all the elements, the solitary vessel is 13 Lieut.-col. Reid, in a recent work entitled 'An Attempt to Develop the Law of Storms,' seems to have clearly proved that those great storms which so suddenly influence the barometer, and are so disas-obliged to continue, without a single breeze to trous to ships, are great whirlwinds, obeying fixed laws; and that so vast is the diameter of their circuit, that, when they reach high latitudes, they frequently extend over 1,000 miles, and perhaps sometimes over half the width of the Atlantic ocean. The proofs afforded in support of this theory consist of extracts from a number of ships' logbooks, from the reports of the correspondents at Lloyd's, from observations by Colonel Reid's brother-officers, and from various other sources of information. These materials, when arranged for each particular storm to which they refer, form in many cases very interesting narratives; the usual interest which we feel in descriptions of disasters at sea being heightened when we find how the incidents are connected. Colonel Reid observes, that in the works of Horsburgh and other navigators the word whirlwind' is constantly used, without any fixed idea being given of the term. He also states that Colonel Capper, of the East India company's service, seems to have been the first to point out that the hurricanes in the bay of Bengal were great whirlwinds, and that Mr. Redfield, of New York, following up the observations of Franklin, has really explained the true nature of the Atlantic storms on the American coast. Most of the storms traced in north latitude were found with a remarkable degree of uniformity to follow courses nearly similar to each other. On examining the charts which accompany the work, we find the storms, whilst still within the tropics, proceeding from the eastward, on a course somewhat to the northward of west, gradually getting further from the equator, and as if going towards the pole. After reaching the 25th or 30th deg. of north latitude, they fall into the general atmospheric current, and then their course is in a north-easterly direction, still continuing further from the equator and nearer to the pole. The sixth chapter of the work on the storms of the southern hemisphere, is thus introduced: assist the mariner's wishes, except those whirlwinds, which only serve to increase his calamity. At present, therefore, this part of the ocean is totally avoided; and, although there may be much gold along the coasts of that part of Africa, to tempt avarice, yet there is something, much more dreadful than the fabled dragon of antiquity, to guard the treasure. As the internal parts of that country are totally unknown to travellers, from their burning sand and extensive deserts; so here we find a vast tract of ocean, lying off its shores, equally unvisited by the mariner. But of all these terrible tempests that deform the face of nature, and repress human presumption, the sandy tempests of Arabia and Africa are the most terrible, and strike the imagination most strongly. To conceive a proper idea of these, "The storm-tracts already traced in north latitude, with few exceptions, are seen to follow nearly similar courses, and in their progress to pass gradually towards the pole. Whilst studying this subject I was led to conclude, that in accordance with the beautiful order and regularity of nature, storms in south latitude would be found to revolve in a precisely contrary direction to that which they take in the northern hemisphere. I therefore earnestly sought for facts to ascertain if this were the case or not." Many instances are given in proof that storms do revolve in the southern hemisphere in a contrary direction tc those of the northern. It is stated, that ships may overtake storms, sailing faster than they move along, and by plunging into them get dismasted, whereas, if the nature of the storm were properly understood, such consequences might be avoided.—ED. ance. we are by no means to suppose them resembling | have been obliged to carry it off in carts. It those whirlwinds of dust that we sometimes see may also be observed, that there are several scattering in our air, and sprinkling their con- particles of iron mixed with the sand, which are tents upon our roads or meadows. The sand- readily affected by the loadstone. The part of storm of Africa exhibits a very different appear the coast that furnishes these sands is a tract of As the sand of which the whirlwind is about four leagues in length, and is upon a level composed is excessively fine, and almost resem- with the sea at high-water. The shore lies in bles the parts of water, its motion entirely re- such a manner as to leave its sands subject only sembles that of a fluid; and the whole plain to the north and east winds, that bear them seems to float onward, like a slow inundation. farther up the shore. It is easy to conceive how The body of sand thus rolling, is deep enough to the same sand that has at one time been borne bury houses and palaces in its bosom travellers a short way inland, may by some succeeding and who are crossing those extensive deserts perceive stronger blast be carried up much higher; and its approach at a distance; and in general have thus the whole may continue advancing forward, time to avoid it, or turn out of its way, as it deluging the plain, and totally destroying its fergenerally extends but to a moderate breadth. tility. At the same time, the sea, from whence However, when it is extremely rapid, or very this deluge of sand proceeds, may furnish it in extensive, as sometimes is the case, no swiftness, inexhaustible quantities. This unhappy country, no art, can avail; nothing then remains but to thus overwhelmed in so singular a manner, may meet death with fortitude, and submit to be well justify what the ancients and the moderns buried alive with resignation.14 have reported concerning those tempests of sand in Africa, that are said to destroy villages, and even armies in their bosom." It is happy for us of Britain that we have no such calamity to fear: for from this even some parts of Europe are not entirely free. We have an account given us in the history of the French Academy, of a miserable town in France, that is constantly in danger of being buried under a similar inundation; with which I will take leave to close this chapter. "In the neighbourhood of St. Paul de Leon, in Lower Brittany,15 there lies a tract of country along the sea-side, which, before the year 1666, was inhabited, but now lies deserted, by reason of the sands which cover it, to the height of twenty feet; and which every year advance more and more inland, and gain ground continually. From the time mentioned above, the sand has buried more than six leagues of the country inward; and it is now but half a league from the town of St. Paul: so that, in all appearance, the inhabitants must be obliged to abandon it entirely. In the country that has been overwhelmed, there are still to be seen the tops of some steeples peeping through the sand, and many chimneys that still remain above this sandy ocean. The inhabitants, however, had sufficient time to escape; but being deprived of their little all, they had no other resource but begging for their subsistence. This calamity chiefly owes its advancement to a north or an east wind, raising the sand, which is extremely fine, in such great quantities, and with such velocity, that M. Deslands, who gave the account, says, that while he was walking near the place, during a moderate breeze of wind, he was obliged, from time to time, to shake the sand from his clothes and his hat, on which it was lodged in great quantities, and made them too heavy to be easily borne. Still further, when the wind was violent it drove the sand across a little arm of the sea, into the town of Roscoff, and covered the streets of that place two feet deep; so that they 14 See Supplementary Note C, p. 170. 15 Histoire de l'Academie des Sciences, an. 1722. "16 Sirocco, so called because it is supposed to blow 16 In Sicily a wind is known by the name of the from Syria. Its medium heat is calculated at 112 degrees: it is fatal to vegetation; and destructive to mankind, and especially to strangers; it depresses the spirits in an unusual degree; it suspends the powers of digestion, so that those who venture to eat a heavy supper, while this wind prevails, are commonly found dead in their beds the next morning, of what is called an indigestion. The sick at that afflicting period commonly sink under the pressure of after this wind has continued a whole night, to intheir diseases; and it is customary in the morning, quire who is dead.-Ed. NOTE A.-Theory of Trade-winds. iell, has entered largely into the history and theory Captain Basil Hall, in a letter to Mr. J. F. Danof trade-winds. The north-east trade-wind," he says, "is conceived to blow from the exact north-east point, nearly to the equator, when it takes a graceful bend, and blows more and more from the east point, till at length it becomes parallel to it; that is, blows from due east. The south-east trade-wind in like manner, is supposed to blow at first precisely at south-east, or at an angle of 45° with the meridian, and at last to assume an exact parallelism with the equinoctial line. This, however, is altogether er roneous. The real state of things is as follows. The trade-winds in the Atlantic and Pacific ocean extend to about twenty-eight degrees of latitude on each side of the equator,-sometimes a degree or two thirty degrees, may expect every day to enter them. farther; so that a ship, after passing the latitude of It will perhaps assist the apprehension of the subject to suppose ourselves actually making a voyage to the Cape, first outwards, and then homewards; by which twice. Shortly after leaving Madeira, which is 324°, means we shall have to cross each of these winds we get into the Trades,' and instead of finding the wind blowing from north-east-as the accounts would lead us to suppose-we shall find it blowing from east, or even sometimes a little southerly. You are seaman enough to be aware that, with the wind at east, a south course can readily be steered, first towards the Canaries, and then to the Cape de Verde islands. It is the most approved practice, I think, to pass just within sight of these islands to the westward of them; that is to say, leaving them on the left hand. As the ship advances to the southward, she finds the trade-wind drawing round gradually from east to north-east, and finally to north-north-east; and even north at the southern verge of the north-east trade. The last-named or northern direction, it will be observed, is at right angles to that usually assigned to it-due east, near the line. The southern limit to the north-east trade-wind varies with the season of the year, reaching at one time to within three or four degrees of north latitude, and at other times not approaching it nearer than ten or twelve degrees; but it never crosses the equator and enters the southern latitudes. It will aid the memory in this matter, to bear in mind that the line, which limits or marks the termination of this trade-wind, follows the sun. In July and August it recedes from the equator, in pursuit, as it were, of the sun; while in December and January, when the sun has high southern declination, it reaches almost to the line. The great difficulty of the outward-bound voyage commences after the ship is deserted by the northeast trade, as she has then to fight across a considerable range of calms, and of what are called 'the variables,' where the wind has generally more or less southing in it. At certain seasons it blows freshly from the south-south-west, and greatly perplexes the young navigator, who, from trusting to published accounts, expects to find the wind, not from south, but from east. This troublesome range varies in width from 150 to 550 miles; is widest in September, and narrowest in December or January. I speak now of what takes place in the Atlantic; for it is not quite the same far at sea in the Pacific ocean, where fewer modifying circumstances interfere with the regular course of the phenomena, than in the comparatively narrow neck formed by the protuberances of Africa and South America. I may remark in passing, that it is upon a knowledge of these deviations from the general rule, which we are pleased to call irregularities, that much of the success of tropical navigation depends. A seaman who trusts to theory alone, will, in all probability, make a bad passage; while another, who relies solely upon past experience, will probably, if the season happens to be different, do quite as badly. The judicious navigator will endeavour to unite the two; and having attentively studied the theory of his subject, and sought to reduce every case to its principles, checking these from time to time by fresh experience, may be able, when occasions arrive where his own knowledge or that of others entirely fails him, to take that course which, all things considered, is most likely to serve the purpose he has in view. tain of finding westerly winds, which prevail in the latitudes beyond the trades' in both hemispheres. Such are the phenomena most generally observed with respect to the regular trade-winds outward bound. We shall now, in order to make things quite clear, invert the order of the voyage, and suppose the ship, after having reached the Cape of Good Hope, to turn back again. At first she may be plagued with westerly and north-westerly winds; but she will generally be able to stretch into the trades,' where she will at first find the wind hanging far to the east, and it may even have some northing in it at first. As she proceeds onwards to St. Helena, which lies directly in the tract of homeward-bound ships, the wind will draw to the east,-east-southeast,-south-east, and, eventually, to south-southeast. At crossing the equator, it will probably be blowing from due south, and not-I must again beg you to take particular notice-from due east, as we are generally led to suppose. After reaching three or four degrees of north latitude, the ship will lose the south-east trade, and re-enter the variables,' where, when it is not calm, she will generally find light southerly winds, and, at one period of the year, namely, about July and August, blowing briskly from the south-west, as far as ten or twelve degrees of north latitude. At other seasons, especially when the sun is near the line, a ship may expect light winds from all quarters of the compass, long calms, and now and then a furious squall, with deluges of rain. But at every season of the year, the homeward-bound passage, or that from the southward, is much easier made than the reverse. On reaching the southern limit of the north-east trade-wind, the seaman finds the wind blowing in his face from the north, (exactly as he formerly met the south-east trade, blowing not from east, but from the south pole,) and is obliged to stretch away to the west-north-west at first, and then north-west, as if he were going to the United States of America not to Europe. As he sails on, and gets more into 'the trade,' it draws round gradually to north-east, and east-north-east, which allows of his coming up' more and more every day, till at length he can steer north-and even north-east; so that he is enabled frequently to look up' for the Azores or Western islands. By-and-by he bids adieu to the north-east trade, in about twenty-eight or twenty-nine degrees of north latitude, as he formerly did of the other trade, in the correspondent degree south. In like manner, also, he will now almost always meet with westerly winds, which will carry him to the channel. It may be remarked by the way, that these westerly winds are not so regular as they are in the southern hemisphere, owing probably to the comparative absence of land, which enables the general principle, by which the winds are produced to act there with greater uniformity. If these descriptions have been rendered sufficiently intelligible to a person who has not before considered the subject, I think he will be in a situation to comprehend the theory: and when that is duly fixed in his imagination, he will find it useful to go back again to the facts stated above, with sharper powers of observation, and a judgment more fitted to arrange and generalize these materials to good purpose. But I am forgetting our voyager. We had reached that spot where the north-east trade-wind left us rolling in a dead calm, or with only an occasional violent squall, accompanied by deluges of rain, in a climate so hot that the slightest cat's paw of wind is hailed with the utmost delight. In process of time, the ship, by taking advantage of every such puff of wind, gets across this troublesome stage of her journey, and meets the south-east trade. It is very material to remark, that this wind does not blow from the east, as the navigator is led to expect, or in a direction parallel to the equator, and which would be to him If air, at any particular spot, be heated, it becomes fair wind; but it meets him, as it is emphatically specifically lighter than the adjacent cooler parts, termed, smack in the teeth. Instead, therefore, of and consequently rises; while its place is speedily steering away south, or south-south-east for the Cape occupied by the contiguous less rarefied or colder air. of Good Hope, he is obliged to keep his wind as Now, the region of the globe lying between the troclosely as possible, and he may think himself fortu- pics, or, we may say, between thirty degrees on each nate, in a dull sailer, if he can clear the coast of Bra-side of the equator, being exposed to the most direct zil without making a tack. As he proceeds on, however, the wind gradually hauls to the south-eastward, then to east-south-east, and at last east, at the southern limit of the trade-winds properly so called. Here, after a little baffling weather, he is almost cer rays of the sun, becomes heated; and the air in contact with this belt, or zone, becoming rarefied, rises with more or less rapidity, according to the circumstances under which the earth is situated. Where an open ocean is found, the incumbent air will be less heated, as in the Pacific, than where districts of dry | ate latitudes both north and south, should be encirearth are found, as in Mexico for instance. The cled with rings of ice. The water might also be partial vacuum thus formed will, in both hemispheres, coloured in order to render the effect visible. Things be supplied by the adjacent air lying, we shall sup- being arranged as above described, and the globe pose, between the latitudes of thirty and fifty de- being supposed for the present at rest, if the division grees. If this be admitted, most of the phenomena between the hot and the cold fluids were removed, of the trade-winds will, I conceive, be readily ex- the cold water would gradually slide along under the plained. It must be granted, however, before pro- hot towards the equator, while the heated water ceeding farther, that a volume of air put into motion, would be carried over the cold towards the poles; is like every other body, possessed with a momen- and, if nothing else were done, that is to say, if the tum, which will continue that motion till stopped by globe were allowed to remain at rest, a mere circular its friction against the fluid through which it is pro-interchange would take place. The temperate porpelled, or by that of the surface of a solid body along tions of the fluid, on coming into contact with the which it may be impelled. Any one who has ob- torrid zone of the globe, and being thereby heated served the ring of smoke sometimes projected from and rendered specifically lighter, would necessarily the mouth of a cannon will understand this; or the rise; while the hot portion, on flowing towards the familiar experiment of blowing out a candle by means cooling substance in latitudes farther from the equaof the air forced from an uncharged gun, by means of tor, would descend to occupy the place of the cold one of the copper priming-caps, affords ample illus- water drawn off to supply the place of the lighter tration that a mass of air once put in motion, will heated water at the equator. A steady current retain that motion like any other portion of matter. would in this way be produced, running below toThe velocity of the earth's rotation at the equator wards the equator, and at right angles to it, and is, in round numbers, 1,000 miles an hour; at lati- above towards the poles: this would evidently be tude 30° it is about 860, or about 140 miles an hour | the only motion impressed on the fluid as long as the slower. . The average velocity of the earth's easterly | globe stood still . motion, in the space between the equator and latitude 30°, may be stated at 950 miles an hour; while | that of the belt lying between thirty and forty degrees, is not much above 800 miles an hour. The superincumbent air at these places respectively, supposing no difference of temperature to exist, would of course partake of the earth's velocity, and there would be an universal calm. But, if we suppose the tropical region to be heated, the air over it will instantly ascend, and take its station above the cold; while the colder and more dense air lying beyond the tropics, will rush in to occupy its place, below that which has been heated. This hardly needs illustration; but, as I have more than once met with people who did not immediately see the consequences which follow from placing two fluids of different density side by side, I may suggest the experiment of a trough, divided, by a sluice in the centre, into two spaces, one of which may be filled with water, the other with quicksilver: both fluids will of course be at rest until the sluice be drawn up, when the heavier fluid will immediately rush in beneath the lighter, and the lighter will flow along above the quicksilver. If, instead of these fluids we substitute hot and cold water the same thing will take place, the cold always flowing under the hot, towards the place formerly occupied by the lower strata of the heated fluid; while the heated portion flows along over the cold, towards the place formerly occupied by the upper strata of the cold fluid. Exactly the same thing will take place if two portions of air, at different temperatures, be the contiguous fluids; though the phenomena will not now strike the senses so strongly. It would not be difficult, I conceive, to have a globe fitted with a contrivance which should represent the operation of the trade-winds; and perhaps a description of such an apparatus will be as ready a method as any other of explaining my views of this theory. Having taken a common globe, I would enclose its tropical region from thirty degrees north to thirty degrees south, in a glass zone or coating concentric with the globe, and also each of the belts lying between the latitudes of thirty and fifty degrees in like manner, with distinct cases placed respectively in close contact with the tropical glass coating, and divided from it by partitions removeable at pleasure; I would fill the tropical case with hot water, and the middle latitude cases, or those embracing the space contained between the latitudes of thirty and fifty degrees in both hemispheres, with cold water; or, which would represent the actual fact still better, a broad ring of heated iron might be fixed round the equator to represent the torrid zone, while the middle or temper It is material to remark here, that this motion would be less and less obvious as the currents approached the equator, where the cold fluid would gradually become heated, and have a tendency to rise as well as to flow along, so that their course would be checked, till at length, at the equator, the opposite currents would meet and produce a calm. While things are supposed to be in this situation, let the globe be put into rapid motion from west to east, we shall say, for the sake of illustration, at the rate of one thousand feet in a minute, while all the circumstances as to temperature remain as before. The cold water would continue to flow just as before, under the hot, towards the equator, where the rarefying cause existed, but it would now come to the equatorial regions, possessed, not only with a motion directly towards the equator, but with the easterly velocity due to that circle of latitude which it had left, or about eight hundred feet in a minute; and if we suppose these equatorial regions to be moving to the eastward at the average rate of nine hundred and fifty feet in the same interval, the cold water moving at the slower rate would inevitably at its first arrival there be left behind; or, which is the same thing, the surface of the globe would go faster to the eastward than the superincumbent water, and this, in effect, would produce an apparent or relative motion of the water from east to west; or, if the fluid in question were air, we should there have what we call an easterly wind. This, in its most general sense, is what really takes place with the trade-winds, and if what I have said be well understood, all the modifications which they undergo will be readily seen to follow. The cold air, however, (it must be carefully observed,) which comes towards the equator, is acted upon by two forces, or, in other words, is influenced by two sources of motion : first, by that which has been impressed upon it in a due easterly direction, by the rotation of the earth in the temperate latitudes it has left: and, secondly, by a motion in the direction o. the meridian, towards the equator, and at right angles to it. This last is caused by the air rushing in to fill up the space left by that which has been rarefied by the heat of the torrid zone, as shown in the first experiment where the globe stood still; in which case, it will be remembered, this was the only motion to which the fluid was exposed. The combined effect of these two motions is to produce the south-east trade-wind in south latitude, and the north-east trade on the other side of the equator. When the comparatively slow-moving air of the temperate zone, caused by the rotatory motion of the |