day after day, by a permanent breeze, farther from their native shores, and inferred the impossibility of returning, as they observed no change in its direction. Fortunately for his fame, and for the world, the great navigator firmly held on his course, reached the bounds of the before supposed illimitable ocean, and re-crossed it in the region of the variables, to the north of the northern trade wind. Now, in passing from the Canaries to Cumana, on the north coast of South America, it is scarcely ever necessary to touch the sails of a ship; and with equal facility the passage is made across the Pacific, from Acapulco, on the west coast of Mexico, to the Philippine Islands. If a channel were cut through the isthmus of Panama, the voyage to China would be remarkably facilitated by the trade winds of the Atlantic and Pacific Oceans, be more speedy, agreeable, and safe, than the usual route by the Cape, the chief interruption to its uniformity occurring in the Caribbean Sea and the Gulf of Mexico, where the trade wind blows impetuously, the sea is stormy, and the sky grey and cloudy.

The theory respecting the origin of the trade winds, adopted by Dr. Dalton, Professor Daniell, and Sir John Herschell, was first proposed by George Hadley, the brother of the inventor of the quadrant, and embodies features of the previous theories of Halley and Galileo, who both grappled with this great geographical phenomenon. It is founded upon the rarefaction of the atmosphere of the torrid zone by the powerful heat to which that region is subject, in connection with the different velocities of the earth's surface, in different degrees of latitude, in the diurnal rotation. Heat rarefies and expands a volume of air in a ratio equivalent to an addition of about seventy feet to the ordinary height of the atmosphere for every degree of thermometrical measurement. As the sun is always vertical at some place within the tropics, the average temperature of the earth's surface in that region, bounded by the parallels of 231° on each side of the equator, is much higher than in latitudes to the north and south; and the incumbent air acquiring this higher temperature, is thereby rarefied and expanded. The consequence is, that in obedience to hydrostatical laws, masses of air are continually buoyed up from the surface, or swelled round the torrid zone in the form of a protuberant belt, the upper strata flowing over, and running off in streams north and south towards the poles, where, having been cooled and condensed, they descend, and flow over the surface towards the equator, pouring in a perpetual current of air to supply the place of that buoyed up by the heat of the tropics. Thus, there is a constant current in the higher regions of the atmosphere, proceeding from the equator northward and southward to the poles; and if the earth were at rest, there would be a constant wind in the lower regions of the atmosphere blowing directly from the poles to the equator, while in equatorial regions the two streamlets would meet and neutralise each other's influence. But the earth is not at rest! It is incessantly whirling upon its axis, the surface moving at a rate which varies according to the extent of the circumference. The velocity at the equator, where the circumference is the greatest, is about sixteen miles a minute; at 30° of latitude, which is below the most southerly point of Europe, it is about fourteen miles in the same time; and at 45°, or about the centre of France, it is about eleven miles. As the distance from the equator increases, north and south, the rate of the rotation thus becomes less, because the circle of the earth's circumference diminishes in extent. Now a current of air flowing from the north or south polar regions, and setting towards the equator, will encounter as it proceeds an increased rotatory motion eastward, the direction of the earth's axical revolution, and, not acquiring the new velocity at once, it will be left behind, and seem to deflect towards the west just in proportion as it does not keep up with the earth to the east. Hence, what would simply be a north or south wind but for the earth's rotatory motion, becomes a north-east and south-east wind as it approaches those regions where, the velocity of the globe being so much greater than where it

originated, it lags behind it in its easterly course. This is the exact path of the trade winds-breezes, with few exceptions, uniform in their direction, perpetual in their motion, and steady in their force-which wafted Columbus across the Atlantic, impelled the Portuguese from their southerly course and bore them to the Brazils, and have since been important auxiliaries to the communication of the eastern with the western continent.

The existence of a current in the upper regions of the atmosphere counter to that below, assumed by the preceding theory, is not mere hypothesis. Clouds, though of rare occurrence in the district of the trade winds, have been observed to take a direction contrary to that which the surface breezes would have given them. A circumstance remarkably in favour of the counter-current inferred from theory, occurred in the year 1812. There was then an eruption of the volcano of St. Vincent, one of the West India islands, which covered the island of Barbadoes with a quantity of the ashes and volcanic matter ejected. The trade wind here blows with great power, and it is certain that the volcanic ashes would have been conveyed in a direction from Barbadoes, instead of towards it, by its action. To account for their transportation thither, it is necessary to suppose, that the volcano ejected them to an elevation within reach of a superior stratum of air blowing contrary to the course of the inferior current. When Humboldt was upon the Peak of Teneriffe the west wind blew with such violence that he could scarcely stand, though the island below was under the influence of the ordinary north-east trade wind; and the remark has often been made, that in the elevated parts of the Canary Islands a contrary wind has been experienced to that which has been prevailing over the general surface.

All mariners and passengers have spoken with delight of the region of the trade winds, not only on account of the favouring gale, but its genial influence, the transparent atmosphere, the splendid sunsets, and the brilliancy of the unclouded heavens, day and night. Columbus, in recording his first voyage into their territory, compares the air, soft and refreshing without being cool, to that of the pure and balmy April mornings he had experienced in Andalusia, wanting but the song of the nightingale and the sight of the groves, to complete the fancy that he was sailing along the Guadalquivir. "It is marvellous," observes Las Casas, "the suavity which we experience when half way towards these Indies; and the more the ships approach the lands so much more do they perceive the temperance and softness of the air, the clearness of the sky, and the amenity and fragrance sent forth from the groves and forests; much more certainly than in April in Andalusia." Humboldt lingers with pleasure, upon his first acquaintance with the tropical regions at sea, upon the mildness of the climate and the beauty of the southern sky, gradually opening new constellations to the view, stars contemplated from infancy progressively sinking and finally disappearing below the horizon, an unknown firmament unfolding its aspect, and scattered nebulæ rivalling in splendour the milky way. "“A traveller," he states, "has no need of being a botanist, to recognise the torrid zone, on the mere aspect of its vegetation; and without having acquired any notions of astronomy, without any acquaintance with the celestial charts of Flamstead and De la Caille, he feels he is not in Europe, when he sees the immense constellation of the Ship, or the phosphorescent clouds of Magellan, arise on the horizon. We pass those latitudes, as if we were descending a river, and we might deem it no hazardous undertaking, if we made the voyage in an open boat. Mr. Bailey, in his Four Years in the West Indies, relates an adventure, nearly answering to that here referred to. The master of one of the small fishing smacks that ply along the coasts of Scotland, who had no other knowledge of navigation than that which enabled him to keep his dead reckoning, and to take the sun with his quadrant at noon-day, having heard that sugar was a very profitable cargo, determined, by way of speculation, upon a trip to St. Vincent, to bring a few hogsheads

of the commodity on his own account into the Scottish market. Accordingly, he freighted his vessel; made sail; crossed the Bay of Biscay in a gale; got into the trade winds, and scudded before them, at the rate of seven knots an hour, trusting to his dead reckoning all the way. He spoke no vessel during the whole voyage; and never once saw land until on the morning of the thirty-fifth day, when he descried St. Vincent's right ahead, and running down, under a light breeze, along the windward coast of the island, came to anchor. The private signal of the little vessel was unknown to any of the merchants, and it immediately attracted notice. The natives were perfectly astonished-they had never heard of such a feat before; and deemed it quite impossible that a mere fishing smack, worked only by four men, and commanded by an ignorant master, should plough the billows of the Atlantic, and reach the West Indies in safety-yet so it was. This relation justifies the title given by the Spaniards to the zone where the trade winds are constant, el Golpo de las Damas, the Sea of the Ladies, on account of the ease with which it may be navigated, the uniform temperature prevalent night and day, and its pacific aspect.

2. Monsoons. These are periodical winds, which sweep the northern part of the Indian Ocean, changing their direction after an interval of about six months, and hence the term Monsoon, the Anglicised form of the Persic mousum, or the Malay moossin, signifying a season, referring to their periodicity. Avoiding all minute detail, we shall merely give the range, direction, and duration of these singular, yet highly useful currents, and that in a very general way. From 3° south of the equator to the northern shores of the Indian Ocean, including the Arabian Sea, the Bay of Bengal, and the Chinese Sea, a south-west wind blows from April to October, and then a north-east wind sets in, and prevails through the next half year, from October to April. From 3° to 10° south of the equator a south-east wind blows from April to October, and a north-west during the suceeding six months. Without attending to local variations, these are the general phenomena. There is a south-west wind prevailing north of the equator from April to October, and southward of this, through a certain space, at the same season, a south-east wind. There is a northeast wind north of the equator from October to April, and coincidently, a north-west wind between 3° and 10° south of the line. The western boundary of the region of the monsoons is the African shore; its eastern limit is supposed to be about the meridian of 136° east longitude, which cuts the island of New Guinea; its northern confine is near the parallel of 27° north latitude, which intersects the Loo Choo islands; its southern extremity has been already stated. The monsoons are much stronger than the trade winds, and may be called gales, but they are by no means of uniform force, either as it respects themselves or each other, the same monsoon occasionally blowing with such violence that ships are obliged to reef their sails. It must not be imagined that these winds are confined to the ocean. They extend over the whole of Hindûstan to the Himalaya, the north-east monsoon bringing copious rains to its eastern shores, and the south-west monsoon performing the same office for its western coast.

The change of the monsoon the periodical shifting of the wind - the most singular feature of the case, is a gradual process, usually occupying about a month, which reduces the reign of the two annual monsoons, north and south of the equator, to five months each, the remaining two months being spent in the transitions. In each interval of change, calms, light variable breezes, alternate with storms of tremendous violence. Mr. Caunter thus describes the scene at Madras, in the interim between the cessation of one monsoon and the setting in of another: "On the 15th of October, the flag-staff was struck, as a signal for all vessels to leave the roads, lest they should be overtaken by the monsoon. On that very morning some premonitory symptoms of the approaching 'war of elements' had appeared. As the house we occupied overlooked the beach, we could behold the

setting in of the monsoon in all its grand and terrific sublimity. The wind, with a force which nothing could resist, bent the tufted heads of the tall, slim cocoa-nut trees almost to the earth, flinging the light sand into the air in eddying vortices, until the rain had either so increased its gravity, or beaten it into a mass, as to prevent the wind from raising it. The pale lightning streamed from the clouds in broad sheets of flame, which appeared to encircle the heavens as if every element had been converted into fire, and the world was on the eve of a general conflagration, whilst the peal, which instantly followed, was like the explosion of a gunpowder magazine. The heavens seemed to be one vast reservoir of flame, which was propelled from its voluminous bed by some invisible but omnipotent agency, and threatened to fling its fiery ruin upon every thing around. In some parts, however, of the pitchy vapour by which the skies were by this time completely overspread, the lightning was seen only occasionally to glimmer in faint streaks of light, as if struggling, but unable, to escape from its prison, igniting, but too weak to burst, the impervious bosoms of those capacious magazines in which it was at once engendered and pent up. So heavy and continuous was the rain, that scarcely anything, save those vivid bursts of light which nothing could arrest or resist, was perceptible through it. The thunder was so painfully loud, that it frequently caused the ear to throb; it seemed as if mines were momentarily springing in the heavens, and I could almost fancy that one of the sublimest fictions of heathen fable was realised at this moment before me, and that I was hearing an assault of the Titans. The surf was raised by the wind and scattered in thin billows of foam over the esplanade, which was completely powdered with the white feathery spray. It extended several hundred yards from the beach; fish, upwards of three inches long, were found upon the flat roofs of houses in the town during the prevalence of the monsoon, either blown from the sea by the violence of the gales, or taken up in the water-spouts, which are very prevalent in this tempestuous season. When these burst, whatever they contain is frequently borne by the sweeping blast to a

considerable distance over-land, and deposited in the most uncongenial situations; so that now, during the violence of these tropical storms, fish are found alive on the tops of houses; nor is this any longer a matter of surprise to the established resident in India, who sees every year a repetition of this singular phenomenon. During the extreme violence of the storm, the heat was occasionally almost beyond endurance, particularly after the first day or two, when the wind would at intervals entirely subside, so that not a breath of air could be felt, and the punka afforded but a partial relief to that distressing sensation which is caused by the oppressive stillness of the air so well known in India." It is an extraordinay but well-ascertained fact, that as soon as one monsoon ceases, though a month may elapse before the succeeding one appears, the clouds take the direction of the approaching monsoon, and thus from the regions of the atmosphere herald its advent to the dwellers below.

We naturally inquire concerning the origin of these peculiar movements, but must be content with a very scanty measure of information upon the subject. The laws which nature obeys in these periodical changes are undoubtedly identical with those which give rise to atmospheric currents in general, but their mode of operation is in this case obscure. The north-east and south-east monsoons, the former on the north and the latter on the south side of the equator, may be considered as trade winds, explicable upon the same principles, but counteracted for a certain time by causes which produce winds from a different quarter, the south-west and north-west monsoons. It has been observed that the south-west monsoon, which prevails to the north of the equator, is coincident with the sun being vertical to that region, when Hindûstan, Siam, and the adjacent countries receive their maximum of heat. Consequently, the incumbent air, being rarefied, ascends, and a rush of colder air to supply its place is produced from the southward, which is then receiving the oblique rays of the sun, and which presenting a surface of water is immensely less heated than the lands to which the luminary is perpendicular. In like manner, the north-west monsoon, which prevails south of the equator, is coincident with the sun being south of it likewise, and vertical to the region, when the sandy plains of Australia become powerfully heated, and the air over them rarefied, creating a wind by the rush of the colder northern air towards the point of rarefaction. These are the explanations commonly given, and though in several respects they do not account for all the phenomena, yet the probability is, that they present the correct theory, anomalous circumstances arising from the influence of causes which are local and as yet unknown. The monsoons are more valuable as auxiliaries to commerce than the trade winds, owing to the change in their direction, for a ship may proceed to a distant port with one monsoon and be aided on its return by its successor.

3. Land and sea breezes. A line in one of our popular songs,

"How sweetly the breeze blows off the shore,"

refers to the wind which begins at evening to blow from the coasts situated between and near the tropics; and an equally grateful breeze blows by day from the sea to the shore in those warm climates. The inequality of the solar action on the land and water, together with the tendency of the atmosphere to preserve an uniform density, is the cause of these periodically shifting currents. During the day the land acquires a temperature higher than that of the ocean, and the air over it is therefore rarefied and ascends, and the cooler air from the sea glides in to fill the partial vacuum produced. At night, the land rapidly cools with the atmosphere over it, but the sea and the air in connexion with it retain a nearly equal temperature, in consequence of which, the colder and heavier land-air displaces the less dense or lighter air over the water, and a wind from the shore is created. The smoke of Vesuvius beautifully exemplifies this diurnal change in the