and the other, 2,542 ounces; which are in the ratio of 8 to 17, being an increase of between one-fifth and one-sixth parts more than the ratio of the surfaces.

Direction of the Winds.] The winds do not move in the same direction through the atmosphere. On the contrary, we frequently observe the wind of the upper regions blowing in a totally different direction from that of the lower. The very loftiest regions of the atmosphere enjoy probably uninterrupted serenity. The winds generally move in a horizontal direction, and hence they receive their names from the quarter of the horizon from which they blow; but we also find currents of air moving in a direction inclined to the plane of the horizon and at various angles. It is a remarkable fact, that violent currents of air pass along, as it were, within a line, without sensibly agitating that beyond them. An instance of this kind occurred at Edinburgh, when the celebrated aeronaut, Lunardi, ascended in his balloon, which was conveyed with great velocity, by the wind, at the rate of 70 miles an hour, while a perfect calm existed in the city and neighbourhood.

Hurricanes.] The most dreadful storms which occur in the atmosphere are the hurricanes by which the Antilles and Mascarenes are so often ravaged. The fury of these appalling phenomena is beyond all idea, they appear to be a horrid mixture and chaos of all the elements, lightning, thunder, rain, hail, and wind, and communicate to the air a velocity surpassing that of gunpowder, which sweeps away every object which it meets with in its course, and lays whole districts bare and desolate. Mr. Stewart, in his View of the Past and Present State of Jamaica, says :— "A hurricane is usually preceded by awful and certain prognostics. An unusual calm prevails; not a breath of wind is felt; the atmosphere is close and sultry, the clouds wild, broken, and perpetually and rapidly shifting; at length a deep and portentous gloom gradually settles and overspreads the hemisphere; the sun is enveloped in darkness; a deep, hollow, murmuring sound, is indistinctly heard, like the roaring of a distant cataract, or the howling of winds through remote woods,-rapid and transient gusts of wind and rain speedily succeed,-various birds of passage are seen hastily driving along the sky, or are thrown down by the violence of these gusts,-even the cattle grazing in the fields, as if instinctively aware of the approaching danger, withdraw to the thickets for shelter. The blasts soon become more impetuous; at one moment they rage with unconceivable fury, and the ensuing instant seem as it were suddenly to expire. In a few hours the hurricane reaches its acme of violence-when all the winds of heaven, and from every point of the compass, winged with destruction, seem let loose from their caverns. The largest trees are thrown prostrate, or shattered and stripped of their foliage; the provision-grounds are laid waste; the sugar-canes levelled to the earth, and in the more exposed situations, torn up by the roots, and wafted about like chaff. Many of the dwellings are blown down, or unroofed, and their inhabitants too often either buried in the ruins, or driven forth to perish unsheltered. Nothing can be more appalling than the wild howling and threatening violence of a hurricane during the night, when the vivid and quickly-succeeding gleams of lightning, darting athwart the heavens, make darkness visible,' and heighten the horror of the scene." Fortunately, however, their duration is usually short, and their sphere of action very limited. Their usual prognostication is a small cloud which appears above some mountain, and spreads out with

great rapidity till it has enveloped the whole mountain; or a copper coloured cloud which rises in a serene sky, and suddenly obscures the whole horizon, after which the tempest bursts forth, and the whole air is thrown into the most violent agitation. The probable cause of these phenomena is thought to be the quick transition of a watery vapour into a fluid, from whence the air rushes in with violence into the vacuum thus occasioned, and a chemical action likewise takes place. Hurricanes are known only in the torrid zones.

Water-Spouts.] A phenomenon not less fearful and destructive in its sphere than the hurricane is the water-spout. Its appearance may be thus described: The sea is observed to become suddenly agitated under a low rainy-looking cloud,—the broken waves appear to collapse towards the centre of the troubled mass of water, and finally seem dissolved into a drizzly vapour, which rises in spiral lines towards the cloud,—at the same moment that this column rises from the sea, another is seen descending in an oblique line from the overhanging cloud, which unites with the former; and the united column, though frequently fifty fathoms broad at the base, seldom presents a greater diameter than that of 2 or 3 feet throughout the greater part of its length. The honourable captain Napier calculated the height of one observed by him at 1,720 feet, or very nearly one-third of a mile. The whole column appears like an empty glass cylinder, and in this form glides rapidly over the surface of the sea, though no wind be observable at the moment; sometimes they move in direct opposition to the prevailing wind, and when several water-spouts are raised at the same moment, they frequently take opposite directions. When the surmounting cloud does not move with the same rapidity as the base of the column, the spout assumes an oblique direction, or even a curvilinear form, and at last is torn asunder with a rushing noise like that of a cataract in a deep valley. In some instances electrical light appears to proceed from the columns, or is excited in the immediate neighbourhood at the moment of its dissolving. It is alleged, and with probability, that water-spouts may be broken and dissipated by the commotion excited in the air by the firing of cannons, which corresponds with the dissipation of thunder-clouds by the ringing of bells. Water-spouts usually appear after storms, or after a long tract of sultry weather, in narrow seas or straits, and occasionally upon large rivers, or lakes. Opposite currents of wind coming in contact with each other with unequal forces, communicate a rotatory motion to the cloud, till it assumes a hollow conical form, and into this tube, assisted no doubt by electrical influence, the waters are drawn up so as to form a waterspout. There is a species of water-spout called a typhon, which is very frequent in the Chinese Sea. The typhon descends not from the clouds, nor is produced by the action of opposite winds. It, on the contrary, rises from the water to the heavens with amazing rapidity. Whirlwinds often run along considerable tracts, bearing down houses, trees, and every obstacle that they meet with. But typhons remain always in the same places, and are probably owing to the action of subterraneous fires; for the sea is then in the greatest agitation, and the air is so impregnated with sulphureous exhalations, that the sky appears to be covered with a copper-coloured crust, although there be no clouds, and the sun or the stars appear through the vapour. Buffon thinks it is to these subterranean fires that we must ascribe the warmth of the Chinese Sea in winter, where these typhons are very frequent.

Peculiar Winds.] The winds generally assume the temperature of the countries over which they blow. They are consequently warm or cold, moist or dry, according to the character of the region from which they proceed. Some winds are likewise distinguished by peculiar qualities and effects arising from the presence of a peculiar air or vapour in excess. The most dreadful of these are the simoom which sometimes blows in Arabia and Persia. The chamsin of Egypt sometimes approaches the Simoom in character and destructive agency. But the harmattan of Guinea and other African districts is a less formidable wind. The description of these peculiar winds, however, belongs more properly to particular geography.

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Utility of the Winds.] The winds purify the air, by carrying off or dispersing noxious exhalations. They also convey the vapours and clouds of one district to another, without which provision of Nature, every district would only receive its own exhalations again by precipitation. They modify the temperature of the atmosphere,-refresh and dry the objects at the surface of the ground,-put collections of stagnant water into motion,—and supply a powerful agency to man in his mechanical arts. Physical Seasons.] As the warmth of the air is the effect of the solar rays, the proximity or distance of places from the sun must occasion a great difference in their respective temperatures: this difference, and the natural phenomena dependant upon it, form the physical seasons. the surface of the earth were a perfect sphere or ellipsoid, everywhere covered with water, the heat would gradually diminish in a certain proportion from the equator to the poles,-regularly follow the course of the sun,—and exhibit the same temperature in the same latitudes; but the different situations, heights, and physical qualities of different regions, cause very striking deviations from this rule. Thus countries lying under the same latitude often possess very different temperatures, and the physical seasons seldom agree exactly with the astronomical seasons which depend on the relative positions of the earth and sun. It is not even possible to give general definitions of the physical seasons.

The torrid zone has only two seasons; viz. the wet and the dry; the former corresponding to the winter-season, and the latter to that of summer, but they are in direct opposition to the astronomical seasons; for the rain accompanies the sun, and when the sun stands in the northern sign, the rainy season begins northwards from the line; and when the sun is situated in the southern sign, it is the dry or summer-season. The contrary of these changes takes place on the south of the equator. The beginning and duration of these seasons happens at regular periods, but is influenced in all other respects by local circumstances, particularly the presence of mountains. Thus, a country intersected by a high ridge runaing from N. to S. exhibits different seasons at the same moment on the E. and W. of the ridge. In some countries there are two summers and two winters, which are distinguished as the long and short summer and winter-seasons. Within 20 degrees of the equator, the difference of heat in summer and winter is usually very inconsiderable; but upon the limits of the torrid zone it becomes more perceptible. The ancients believed the torrid zone to be uninhabitable, on account of the extreme heat which

they supposed must rest there. But this heat is much tempered by various causes. The clouds which veil the sky in the rainy seasons absorb the sunbeams, and the violent gushes of rain which happen at this season greatly moderate the heat. The nights are even cold, being

almost throughout the whole year of equal length with the day, and consequently long enough to cool the earth considerably. The vast extent of ocean, and the prevailing east winds, also temper the heat; while the elevated situation of some districts greatly reduces the temperature. Quito enjoys a moderate climate, and extreme cold is felt upon the neighbouring Cordilleras. The greatest heat exists probably in the interior of Africa, and the countries of Senegambia and Guinea. Nothing can equal a tropical summer in magnificence. The cloudless sky reflects an intense light during the day,-and at night the light of the moon and the splendour of the milky way illuminate the whole heavens, while the serene repose in which all nature seems wrapt, produces the most pleasing effect on the mind of the spectator.

The temperate zone approximates very closely in climate to the torrid zone in its immediate neighbourhood; but the difference of seasons becomes visible as the distance from the limits of the latter increases. In physical respects, spring is here that season when the cold of winter yields so much to the heat of summer, as to allow the plants to put out their blossoms; summer is the season during which the fruit attains maturity; autumn that of harvest and the departure of the passage-birds, till whose re-appearance winter endures. It seldom snows in low countries till we reach the 40th parallel; but the trees lose their leaves during the short winter. The difference of seasons is most observable between the 40th and 60th parallels. Here the weather is most changeable, and local circumstances produce the greatest diversity of climate. Spring and autumn gradually shorten as we proceed towards the high north; and in the neighbourhood of the Polar zones we again observe only two seasons, the short summer and long winter, bordering so closely upon each other, that in the short space of a few days, hardly deserving the name of a season, vegetable life springs into activity. The summer is late, but hot, the power of the oblique sunbeams being assisted by the length of the days; but the cold of winter is so extreme, that brandy freezes even in closed apartments. In the district of Bigorre, in the French Pyrennees, there are only two seasons,-summer instantly succeeds to winter, and cool nights to intensely warm days.

Physical Climate.] The real, or physical, climate of a country agrees as little with the mathematical climate, as the physical seasons with the astronomical. The mathematical climate, however, which depends upon the absolute effect of the sun, its relative situation, and the length of the days, forms the basis of the physical climate. But the latter is modified by the physical qualities of a country; viz. its height above the level of the sea, the inclination of its mountains, the character of its soil, and the reigning winds.

With the elevation of a country the temperature decreases. Coast districts are always less cold than the inland ones, and that not merely because they are usually less elevated, but also because the sea preserves a more equable temperature, which it communicates to the adjoining country. Hence it happens, that Bergen, in Norway, under the 60th parallel, enjoys a milder climate than the middie of Germany under the 50th. Coast districts, however, are subject to more frequent and rapid changes of weather, and to storms. Mountains strengthen or impede, according to relative situation, the effect of the sunbeams and the wind The severe cold of Siberia is in a great measure attributable to the position of the mountains, which lying southwards, expose it to the north

winds, while they check the southern breezes. Sweden and the south of Norway owe their comparatively mild climate to the range of the Scandinavian Alps, which protects them against the rough north winds. Wooded mountains are of great utility, particularly in islands, by collecting and condensing the clouds into fertilizing rain, and the destruction of the woods in the Cape Verd islands, has been followed by the drying up of the springs and streams. An interesting and able investigation into the supposed changes in the meteorological constitution of the different parts of the earth, during the historical period, has been made by M. Schow, Professor of Botany in the University of Copenhagen; and, after an extensive examination of all that the ancients have left us, connected with their botany and agriculture, compared with our present experience on those subjects, the author thinks himself entitled to assume that the climate of Greece and Italy, like that of Palestine and Egypt, has undergone no important change since ancient times. But if, on account of the later harvest and the possible growth of the beech-trees in the Roman plains, we might be led to the opinion that formerly the climate had been a little colder than now, the difference will hardly come up to one or two degrees, and will not be greater than might be occasioned by the cultivation of the North of Europe. The quality of the soil modifies the climate, because all kinds of earth do not acquire an equal temperature under the same circumstances, and because incessant exhalations rise from the soil into the atmosphere, partaking of the nature of the substances from which they are detached, and communicating these qualities to the air. Thus, a dry sandy soil, every where acted upon by the sun's rays, as in the deserts of Arabia, heats the air, while the exhalations from the thick woods and putrid marshes of Batavia load it with the most noxious particles; and the quantity of saline particles which are present in the soil of Siberia, greatly contribute, upon well-known chemical principles, to increase the cold of that district. Hence too the happy change which agricultural art always effects upon the climate of a country. The Germania sylvis horrida of Tacitus is no longer to be recognized by the stern forbidding features under which that accurate observer beheld it; and those districts of our own country, once impenetrable to any foot save that of the wild beast, or his almost equally savage hunter, are now the abodes of peace, health, and plenty. It has been alleged, in the case of the valley of Aran, in the district of Bigorre, already instanced, that cultivation has rendered that tract of country less healthy, because the clouds now sweep over the country instead of being attracted and dispersed by the woods, which also no longer present their barrier to the scorching south-wind. Castile and Arragon are likewise represented as furnishing similar cases. But it seems probable that these instances have been overstated; and allowance must be given for the infant state of agriculture in these districts, for all countries necessarily suffer more or less during the earliest stages of agricultural improvement, when the lands are first thrown open and proper means have not been adopted for their draining and inclosing. The reigning winds render the climate of a country more or less humid. The winds coming from the nearest pole in the temperate zone bring serene and dry weather, and the winds blowing from the equator produce damp and misty weather.

The Thermometer.] The thermometer, long after its invention, remained a very rude and imperfect instrument, both in its construction and graduation. Water, oil, and alcohol, were successively used to fill it; but