XVI. of the water-spout move with unequal velocities, the lower BOOK cone is often seen to incline sideways, or even to bend, and finally to burst in pieces. A noise is then heard like that of a cataract falling in a deep valley. Lightning frequently issues from the very bosom of the water-spout, particularly when it breaks; but no thunder is ever heard.* Philosophers explain this phenomenon in the following Origin of manner: Two winds meet; a vortex ensues; any cloud spouts. which happens to lie between them is condensed into a conical form, and turned round with great velocity. This rotation impresses all the particles of the cloud with a centrifugal force; they are driven towards the exterior surface; a vacuum is produced within, about the axis of the cone; water or any other body lying beneath this vacuum, is carried into it by the effect of gravity striving to re-establish an equilibrium. Having considered the general and the modifying causes of winds, let us now trace, with greater minuteness, such of those atmospherical movements as, by their regularity and extensive occurrence, are most important to geography. water Atlantic In the Atlantic Ocean, the general east or trade-wind Tradeprevails up to the 32d or the 28th degree of north lati- wind in the tude, according as the sun is in this or the other hemi- Ocean. sphere. On the north-east coasts of America, the tradewinds extend as far as 40 degrees; a fact evidently shewing that currents in the atmosphere, like currents in the ocean, grow broader as they proceed while, on the other hand, the east winds, like the westerly movement of the ocean, do not begin to produce a vigorous effect, till they have reached a certain distance from the eastern continent, their point of departure. The same peculiarity occurs in the Ethiopian Ocean, where the east wind extends, in like manner, some degrees farther on the coast of Brazil, than near the Cape of Good Hope. As those east winds always *Voyages of Dampier, Thévenot, Le Gentil, &c. Encyclopédie Méthod. Marine, tome iii. partie 2d, p. 791. Forster, Observations on Physical Geography, p. 93, (in German.) XVI. Winds in the Gulf of Guinea. BOOK receive the impulse of the two polar atmospheric currents, at an angle approaching more or less to a right angle, they change into north-east in the northern hemisphere, and southeast in the southern hemisphere. But on approaching the coasts of America, the general east wind resumes its force, overcomes the effect of the polar currents, and follows its own direction from east to west, with more or less exactness. On the coast of Guinea, particularly from Sierra Leone to the Isle of St. Stephen, south and south-west winds prevail over an extent of 500 leagues of shore. They turn more to the south-west and west, as we approach the land. If to this circumstance be added the fact, that, in Guinea, there sometimes occurs an east wind of extreme violence, it appears natural to regard those two movements as having a direct connexion; and the south and south-west winds will thus be nothing more than partial currents of the general trade-wind, attracted to the vast continent of Africa, where the air is prodigiously rarefied by means of the solar rays reflected from its burning sands. But as the general trade- · wind must, notwithstanding, sometimes produce its effect in the interior of that continent, those great masses of air, accumulated and condensed on the central platform of Africa, will now and then make violent eruptions. Region of calms. On the confines of the two trade-winds, in the western ocean, between the fourth and 10th degrees of north latitude, and the 330th and 365th of longitude (from Ferro,) there is a space of sea where navigators find perpetual calms, accompanied by a suffocating heat, by thunder-storms and dreadful lightning, with rains so frequent and so copious, that this tract has been called the rainy sea. The slight winds that occur here are but sudden squalls, of short duration and little extent; so that sometimes every hour affords a different wind, which degenerates into a calm before another succeeds it. Calms prevail equally about the common limits of the trade-winds and variable winds; but, in these cases, they BOOK are soon destroyed by blasts and tornadoes. XVI. It is from observing this habitual condition of the atmo- Tornasphere, that fixed methods have been laid down for sailing does. to and from the continent of America. In the first case, a navigator always endeavours to get southward to a latitude near the tropic, because in that quarter he is sure of finding a fresh easterly or north-easterly wind, which, joined to the prevailing current, will rapidly drive him towards the American coast. For returning to Europe, he endeavours to reach at least the 30th degree of latitude; because it is here that the winds first become variable, though still more frequently they blow from south-west. winds of In the Great Ocean, or Pacific Sea, we again find the Tradegeneral movement of the atmosphere from east to west, mo- the Pacific. dified by the two polar currents. The vast extent of this sea allows the atmosphere to unfold its natural 'movements in a regular manner. The north-east and the south-east winds are here so steady and strong, that, if at Panama, in place of an isthmus, there were a strait, the voyage to China would be accomplished much sooner by sailing westward than by sailing eastward. As those movements set out from America and the Andes mountain-chain, they are more feeble and circumscribed on the coast of America, where they begin, than near or even within the tropics. On the opposite coasts of Asia and the regions to the south, they extend as far as the fortieth parallel. In sailing from Acapulco to the Philippines, the Spaniards simply allow themselves to be carried forward by the winds and currents, which drive them in a straight line, and very speedily, to their place of destination; and this is the reason why, though navigating that ocean so long, they have discovered so very few of those southern regions, from which they were frequently at no great distance. In returning to Mexico, they ascend as far as Japan, and then direct their course to the north-west coast of California. This great extent of the trade-winds must be attributed to the weakness of the polar currents, aërial as well as marine; BOOK Monsoons, or half yearly India. while it is the superior strength of the south polar currents which causes south winds to prevail along the coast of Peru. It is in the Indian Ocean alone that the famous monsoons, or half yearly winds, seem to destroy the uniformity of the winds of general atmospheric movement. No doubt, however, they might be made to accord with it, provided we know all the circumstances which influence them. We exhibit the facts in the first place. From the 10th degree of south latitude to the tropic of Capricorn, and beyond it, the general east or south-east trade wind prevails over all the Indian Ocean, sometimes in summer extending as far as the 2d and 3d degrces of south latitude. On this side the 10th degree, we first meet with the monsoons* or periodical half yearly winds. North of the equator, from April to October, a violent south-west wind prevails, accompanied with tempests, storms, and rain; while a soft and pleasant north-east wind blows during the other six months. Between the second and twelfth parallels of south latitude, the winds blow generally from north-west during the winter six months, from south-west in summer.t Varieties in the During winter, then, the constitution of the atmosphere exhibits the following principal circumstances: North-east winds north of the line; north-west winds south of it, to the 10th parallel; and finally, the east and south-east tradewinds. In summer, the phenomena are less contradictory: South-west winds from the 10th parallel to the northern limits; trade-winds south of the 10th parallel. These general tendencies are subject to variations, deMonsoons. pending on the figure and elevation of coasts, on straits, and currents of the sea. The north-west and south-west monsoons are weaker and more variable in the Bay of Bengal, more steady and violent in the gulf of Arabia. Both those monsoons grow broader to the west, ranging in this direction over the whole tract of sea that lies between Af From a Malay word, moussin, signifying season. + Moore's Practical Navigation, 12th edit. London, 1796, p. 124, et seq. XVI. rica and Madagascar. In the seas extending between Chi- BOOK na, the kingdom of Siam, Sumatra, and the equator, those monsoons are felt likewise; but here, excepting local variations, they are almost entirely north and south. They extend as far as the Philippine Islands, and though with much inconstancy, even to Japan. Between the equator, the island of Java, and New Guinea, the monsoons are nearly similar to those of the Chinese Sea, in regard to their direction, which merely varies a little to the northwest in the north monsoon, and a little to the south-west in the south monsoon. But they do not begin till six weeks monsoons change. after those of the Chinese Seas. Some other striking circumstances still remain to be no- How the ticed. The monsoons do not change, or, as sailors express it, do not break, of a sudden. Their change, which usually takes place fifteen days or four weeks after the equinoxes, is announced by the decay of the existing monsoon, by calms and squalls in rapid succession, by storms, water-spouts, tornadoes, and by Indian hurricanes, called taifouns, particularly terrible from the explosions of electric matter accumulated by the monsoon. The beginnings of the subsequent monsoon are, at first, liable to variations, till finally it establishes an absolute dominion. winds. Navigators assert, that, on quitting the region where a Double monsoon prevails, one is sure, in ordinary circumstances, to fall in with a very strong and impetuous wind, blowing from a quarter directly opposite. They must naturally have observed this phenomenon with much care, since the calms and whirlwinds it occasions are productive of great danger. It can hardly be explained, except by admitting, with Halley, the existence of two currents,-one above, composed of warm and rarified air; another below, composed of the column of cold and condensed air. This hypothesis will become almost a settled truth, if we observe how small is the elevation to which the monsoon extends-a fact clearly exhibited in the peninsula on this side the Ganges, where the monsoons are arrested for several months by the mountain chain of the Gauts, (not certainly of extraordinary |