as the sun at that period is vertical, or nearly so, the summer heat, on which the line of perpetual snow depends, is greater than directly under the equator. The gradual decrease of temperature at increasing elevations above the level of the sea, has a marked and very beneficial effect, in diversifying the climates over the surface of the globe, and in fitting it for the production and maintenance of an almost endless variety of plants and animals. All countries situated between the tropics are subject to an excessively high temperature; and in such localities, when the land is nearly level with the sea, the heat is extreme ; and unless furnished with most abundant supplies of rain, they present a highly parched and arid appearance; such regions being more destitute of vegetation, and consequently of animals, than almost any others on the surface of the globe. Of this description is the Sahara, or Great Desert of Africa. Where tracts of land occur, similar in latitude and elevation, but abundantly supplied with rain, the most luxuriant fertility prevails, enlivened by innumerable tribes of animated beings, but usually insalubrious, and unfitted for the abode of man. Such are the swampy and pestilential shores of Comayagua, or Honduras. At an elevation of about 3,000 feet above the sea, however, a totally different climate prevails; thus, the elevated lands of Central America, at no great distance from the last-mentioned district, are described by Colonel Galindo, as presenting the most delightful climate imaginable, where "perpetual spring and verdure ever exist, and realize the dream of the ancient European poets, who, without experiencing it, imagined a similar climate for their favourite Elysian fields, or the island of Calypso." At still greater elevations we arrive at the line of perpetual snow. The mountains of Central America, or Guatemala, however, scarcely attain that height above the sea; but the Andes present a vast number of snowcapped summits within the torrid zone. The snow-line, as has been already observed, is subject to variation in different localities, though situated in the same parallels of latitude. Thus, it appears that an elevated plain, or table-land, in the vicinity of a mountain, tends to elevate the temperature of the mountain, and consequently to raise the snow-line, which will be found to be higher on a mountain so situated, than on one that is isolated, or where the ascent is more sudden and precipitous. As it has just been stated, that the temperature of elevated land is not so high as that of low plains, we might expect the very reverse to be the case. A familiar illustration, if we may be permitted to introduce it, will perhaps afford the clearest explanation of this phenomenon. The higher temperature on mountains so situated, appears to be owing to the effect produced on the atmosphere by the radiation or the reflection of the sun's rays from the high table-land; an effect very similar to this may be observed in our own dwellings. If the windows of our apartments are situated near the ground, we may, in hot sunny weather, perceive that the temperature of our rooms is increased by the reflection of the sun's rays, more especially if they fall on a stone pavement, for the amount will vary according to the nature of the surface; and should it consist of turf or meadow land, the reflection will be scarcely perceptible. If, then, we ascend into our upper apartments, we shall find the reflection from the stone pavement-partly Owing to the greater distance, and partly to the different angle or direction from the ground to the upper window— will, if not wholly without effect, be far less intense, and will communicate little or no heat to the upper rooms. Should, however, a balcony, or a portico, extend in front of our upper windows, this will form no bad representation of a table-land adjoining a mountain; and will, by reflecting the sun's rays directly into our upper rooms, elevate their temperature. The stupendous Himalaya mountains afford a striking instance of the effect produced by such an elevated tableland. On the southern side of this mighty range, in lat. 30°, the snow-line commences at the elevation of about 12,500 or 13,000 feet above the level of the sea; whilst on the northern side, where, from the aspect, we might be led to expect a greater degree of cold, the snow-line does not descend below 16,000 feet above the sea. Our readers will readily perceive that this is capable of a satisfactory explanation, when they are reminded that the northern declivity of this mountain mass terminates in the immense elevated plains of Tibet, the surface of which exceeds 10,000 feet above the level of the sea; whilst on the southern side, the mountains rise directly to a great elevation, from a flat country scarcely 1,000 feet above the sea, and covered with a close jungle; of all descriptions of surface the least favourable for radiating heat. In high latitudes, however, where table-lands occur of sufficient elevation to be covered with snow during the greater part of the year, the very reverse takes place; and in such situations, the temperature will be lower on mountains so circumstanced, than on such as are isolated. And it has even been observed that, in sunny calm weather, the temperature on isolated mountains, in very high latitudes, increases with the elevation. Thus, in Spitzbergen, the temperature at a lower station was found to be about 36°; and at the summit of a mountain, 1,542 feet above the sea, it rose to 40°. Among the causes which produce some effects on the climate of any region, though not so important as the preceding, is the nature of the soil. This is principally owing to the greater or less power any soil possesses of radiating heat. Thus, sandy soils are subject to become rapidly and intensely heated, and when the sun's rays are withdrawn, they readily radiate, or impart to the atmosphere, the heat they have acquired, thus increasing the general temperature. Clayey soils, on the other hand, become slowly heated, and as slowly part with heat. Swampy ground chills the air, and extensive forest tracts have a similar effect. And thus, cultivation not unfrequently effects a change in the climate of any country; for if marshes are drained, or forests cleared, the temperature will be raised. Such has been the case in some parts of North America, where the clearing of the forests and the progress of cultivation have improved the climate, and rendered the winters milder. The destruction of woods has, however, proved highly detrimental to the climate of some regions. Thus the sultry atmosphere and dreadful droughts experienced in the Cape Verde Islands, are attributed to the destruction of the trees in those islands; whilst a remarkable improvement has taken place in the climate of the Island of Ascension since that has been brought into cultivation. The prevailing winds produce considerable effect on the climate of any place; and at the same time the character of a wind depends on the nature of the surface over which it passes, and consequently on the configuration of the land, and the relative position of land and water. The prevailing winds of Great Britain and Western Europe, sweep, as we have seen, across the vast Atlantic Ocean; their character is, therefore, usually mild; and those regions are not subject to extremes of heat or cold. If the wind, in lieu of crossing an expanse of sea, pass over a large tract of land, its character will be greatly influenced by the nature of the surface over which it sweeps. This is illustrated by the character of the easterly winds in the eastern counties of England. These winds, before they reach our shores, cross the vast plains of Northern Germany. In the latter part of the spring, the surface of those plains is damp and chilly; and the intervening sea not being of sufficient extent greatly to temper them, they bring with them a cold and chilly character, which, especially in our eastern counties, renders these winds at that season so ungenial, and not unfrequently injurious to vegetation. Yet even, These seeming cruel winds Blow not in vain: far hence, they keep repressed Those deepening clouds on clouds, surcharged with rain, In endless train, would quench the summer blaze, And cheerless drown the crude unripened year. But though in spring and early summer these winds are chilly and damp, in the autumnal months they assume a totally different character. At that season, the plains of Germany are usually dry and sandy; they accordingly become warmed, and also radiate a considerable degree of heat. The consequence of which is, that the easterly winds acquire a higher temperature in passing over them; sometimes, indeed, sufficient to raise the thermometer several degrees on our eastern shores at that period of the year. The position of mountain ranges may also be mentioned as producing considerable effects on the climate of any region; more especially if extending from east to west, and thus screening it from the north, or leaving it unsheltered in that direction. Of this, the different climates of Poland and Hungary afford a striking example. The Carpathian Mountains form the separation between the two countries; and Poland, situated to the north of this range, and having no elevated land to protect it from the piercing blasts which sweep across the plains of Northern Europe, suffers from a very cold and humid climate, the winters being nearly as severe as in Sweden. Hungary, on the contrary, sheltered by the Carpathian Mountains from the cold blasts of the north, and sloping gently towards the south, enjoys a milder climate than any part of Germany. The currents of the ocean may be considered as very influential causes of the diversity of climate. The principal currents are produced by the movement of the waters, perpetually setting from the polar regions towards the equator; and by the progression of the tropical seas towards the west; both of which originate in the earth's diurnal rotation. By the laws of mechanics, any fluid body in rotation has a tendency to culminate, or accumulate in a heap at the part in most rapid motion; and accordingly we find the waters of the polar circles naturally flowing from their own stiller region, to that of the more rapidly revolving equatorial zone. Powerful currents are thus formed; which in some instances bear with them vast masses of ice, these being carried to |