prevalent in our latitudes, as well as the almost constant westerly winds of the North Atlantic.

But although the trade-winds blow with remarkable constancy in the wide ocean, their general direction is affected by the proximity of land, and a deviation from their regular course may be observed near the shores of America, and yet more strikingly off the coast of Africa, in which region, especially in the vicinity of the Sahara, the air becomes more heated than over the sea, giving rise to sudden changes and violent storms, which are of frequent occurrence on that coast.

The monsoons, or periodical winds of the Indian Ocean, also owe their origin to the proximity of land. In the southern portion of the Indian Ocean, which is remote from this cause of disturbance, the trade-wind blows from the south-east with its wonted regularity; but in the seas between Sumatra and Africa, which form its northern belt, the course of the trade-wind is reversed for half the year, during which period there is a constant wind from the south-west. This change occurs from April to October, and appears to be occasioned by the great rarefaction of the atmosphere, in the extensive regions of Southern Asia, at that season of the year, the sun being then north of the equator. These winds are distinguished as the southwest and north-east monsoons; the former of which, passing over the ocean, arrives charged with moisture, and depositing copious supplies of rain, renders the vegetation of India so splendid and beautiful at that season of the year.

Sea-breezes are produced by causes similar to those which give rise to the south-west monsoon. The surface of land being more heated during the day than that of the sea, and the air consequently becoming rarefied, rises, and the cooler air, being heavier, rushes in from the surface of the sea, thus giving rise to the sea breeze; this usually commences about ten A.M., and continues throughout the day, until about six in the afternoon, when it gradually dies away. In some situations the reverse takes place at

night, the sea at that time retaining a higher temperatur than the adjacent land, and causing a land-breeze to rise this usually commences about eight in the evening, and die away before six or seven in the morning; it is much fainte and less regular than the sea-breeze, and also of much les general occurrence, requiring particular conditions of surfac for its production :-the sea-breeze, on the other hand, i more or less felt on the coasts of all warm countries, and ir hot sunny weather may even be observed on our own shores

In temperate climates, the winds are far less regular than in tropical regions, the general causes which produce them acting with less force and constancy, and the disturbing causes being therefore less under control. The most prevalent winds of Great Britain are from the south-west, attributable, as we have just seen, to equatorial heat and the rotation of the earth.

The hurricanes of the West Indies, the typhons of the China Seas, and the ox-eye of the Cape, where,

Amid the heavens,

Falsely serene, deep in a cloudy speck

Compressed, the mighty tempest brooding dwells;

are all violent and extraordinary agitations of the air, appearing to have a rotatory motion, being analogous to whirlwinds, and sweeping round, in a regular course, from one point of the compass to another. The tornadoes of the western coast of Africa, the pamperas of South America, and the storms called arched squalls, are considered by Colonel Reid to be of a different character.

The sirocco of Italy and Sicily, and the solano of Spain, as well as the simûn, or simoon, of Arabia, and the harmattan of Western Africa, are all winds which owe their origin to the heated surfaces of the sandy districts of Arabia and Africa. The principal difference between these winds appears to be, that the two former acquire some moisture in crossing the Mediterranean, and consequently have not that excessive aridity which characterizes the simûn and the harmattan.

THE term climate is used to express the combination of temperature and moisture which prevails in any particular region. The most prominent causes of diversity of climate are, the heat of the sun; the relative position of land and water; and the elevation of land above the level of the sea. To these may be added, as producing considerable, though less marked effects: the nature of the soil; the prevailing winds; the position of mountain ranges; and the currents of the ocean.

The sun is the grand agent in diffusing heat over the surface of the globe; the temperature of any part, mainly, if not wholly, depending on its exposure to his rays: this being, however, modified by circumstances, the power of the sun's rays being great in proportion to the vertical direction in which they strike the earth. Whenever the sun is above the horizon of any place, that place is receiving heat; when below, parting with it, by the process called radiation. Whenever, therefore, the sun remains more than twelve hours above the horizon of any place, and consequently less than twelve hours beneath, the general temperature of that place will be above average; and when the reverse occurs, it will be below average. As the earth revolves on its axis, successive portions of its surface are heated by the solar rays; and, owing to "the simple yet stupendous contrivance of the inclination of the axis of the earth to the plane of its orbit," the northern and southern

hemispheres are brought alternately more directly unde: the solar influence; and not only do we thus enjoy the varieties of day and night, and the grateful change of the seasons, but by this means the heat of the intertropical zone is moderated, and the limits of the temperate regions greatly extended.

The division of the earth into five zones, the torrid, the two temperate, and the two frigid, may convey a general idea of the temperature of these respective portions of the earth's surface; and in fact, did the temperature of any place depend solely on the heat of the sun, this arrangement, or any other, dividing the earth's surface into parallel bands, might present a correct indication of the temperature of each zone. The power of the sun's rays is, however, so modified by other circumstances, that great varieties of temperature are observed to prevail in countries situated in the same parallels or degrees of latitude. Thus, by some observations recently made at New Archangel, on Sitka Island, situated immediately off the western coast of North America, in lat. 57°, it appears that the mean annual temperature at that place is nineteen degrees higher than at Nain, on the coast of Labrador, in the same parallel of latitude. The difference between the winter temperature of the two stations is yet greater, amounting to no less than thirty-six degrees. At Sitka, the snow never lies long on the ground, but usually disappears as soon as it falls. In Labrador, on the other hand, there are hardly two months of the year perfectly free from ice and snow; and the latter accumulates on the plains near the sea, to the depth of twenty or twenty-four feet. In the interior of the continent, at Fort Chippewyan, in the same parallel, the summers are much hotter than at Sitka, and the winters more severe even than at Labrador, the thermometer sometimes falling to 20° or 30° below zero. Nor is this remarkable difference of climate confined to the New World; it is also observable in the Old, of which the respective climates of Kamtchatka and Great Britain may be mentioned as an

instance.

This variation of climate appears, in great measure, to be attributable to the different arrangement of land and water, which has been already mentioned as one of the principal causes of diversity of climate.

The waters of that great "climate agent,” the ocean, are of very equal temperature, and have, therefore, a tendency to preserve a similar mean, or equal temperature, wherever their influence extends, moderating alike both heat and cold. Thus, when a cold wind passes over the sea, it becomes warmed, and the cold of winter will be moderated. A hot wind, on the contrary, becomes cooled in passing over the sea, and the summer temperature of the adjacent regions will be lowered. And hence we find that the climate of. islands, and of countries bordering on the sea, differs considerably from that of the interior of continents, the former being usually characterized by milder winters and more temperate summers. Such countries are said to possess an insular climate. When, on the other hand, any region experiences great severity of cold in winter, and at the same time, a considerable degree of heat in summer, it is said to possess an excessive climate. Thus, Sitka has an insular climate, the summer temperature being low, and the winter moderate; but Fort Chippewyan presents an instance of an excessive climate. Labrador, from its littoral or coast situation, might seem entitled to an insular climate, but the difference between its climate and that of Sitka, is supposed by M. Baer to arise from the configuration of the land; Sitka being completely screened from the influence of the circumpolar regions by the peninsula of Alyaska, and its continuation in the Aleutian Isles, which in general form a range of high land, protecting it from the north and east, and preventing the ice of the arctic regions from drifting to its shores; whilst, at the same time, it is open to the influence of the warm currents flowing from the equatorial regions of the Pacific. Labrador, on the contrary, has no intervening land to protect it from the north, or from the icebergs which are formed in Baffin's Bay, from whence a current sets

E