I. Differences of the Seasons from the Equator to the Polar Circle. This table shows the increase of the difference between the winters and summers from 28° and 30° to the parallels of 55° and 65°. The increase is more rapid in the Transatlantic zone, where the isothermal lines of 329 and 50° approach one another very much; but it is re markable that, in the two zones which form the two systems of different climates, the division of the annual temperature between winter and summer is made in such a manner that, upon the isothermal line of 32°, the difference of the two seasons is almost double of that which is observed on the isothermal line of 68°. If, instead of the mean temperatures of the seasons, we consider, I do not say the days of the maxima and minima of the year, which are the ordinates of the concave and convex summits of the entire curve, but the mean temperatures of the warmest and the coldest month, the increase of the differences becomes still more perceptible. We request the reader to compare, in the following table, only the places which belong to regions bounded by the same meridians, and consequently to the same system of climate; as, for example, to the region of Eastern America to that of Western Europe and that of Eastern Asia. We must also attend to the changes of temperature produced by the monsoons in a part of the equinoctial regions, and distinguish, under the temperature zone, between the climate of the interior, or the continental climate, and that of islands and coasts. We may conclude, in general, that, for any given place in the curves which express the annual temperatures, the ordinates of the concave and convex summits differ the more from one another, as the temperatures diminish. In the New World, under 40° of latitude, we find a greater difference between the warmest and coldest months of the year than in the Old World, at Copenhagen and Stockholm, under 56°59° of latitude. At Philadelphia, the thermometer descends to 50° or 59° below the freezing-point, while, under the same parallel in Europe, it descends scarcely 30.6 below it. On high mountains in islands of little extent, and along the shores, the lines of annual temperature take nearly the same form as in warm climates, having only a less degree of curvature. The difference between the seasons, too, becomes smaller. At the North Cape, in 71° of latitude, and in the isothermal line of 32°, it is almost 11° greater than at Paris, in 49° of latitude, and in the isothermal line of 50°. The sea-breezes and the fogs which render the winters so temperate, diminish at the same time the heats of summer. The characteristic of any climate is not the difference between the winters, expressed in degrees of the thermometer: it is this difference, compared with the absolute quantities indicated by the mean temperature of the seasons. II. Difference between the Winters and Summers, in following the same Isothermal Line from West to East. The differences between the seasons of the year are less great near the convex summits of the isothermal curves, where these curves rise again towards the North Pole, than near the concave summits. The same causes which affect the inflexion or the greatest curvature of the isothermal lines, tend also to equalize the temperatures of the seasons. The whole of Europe, compared with the eastern parts of America and Asia, has an insular climate; and, upon the same isothermal tine, the summers become warmer and the winters colder, in proportion as we advance from the meridian of Mont Blanc towards the east or the west. Europe may be considered as the western prolongation of the old continent; and the western parts of all continents are not only warmer at equal latitudes than the eastern parts, but, even in the zones of equal annual temperature, the winters are more rigorous and the summers hotter on the eastern coasts than upon the western coasts of the two continents. The mean temperature of the year being equal to the fourth part of the winter, spring, summer, and autumnal temperatures, we shall have upon the same isothermal line of 53:6 (12° cent.) This analogy between the eastern coasts of Asia and America sufficiently proves that the inequalities of the seasons, of which we have endeavoured to fix the numerical relations, depend on the prolongation and enlargement of continents towards the pole; of the size of seas in relation to their coasts; and on the frequency of the N.W. winds, which are the vents de Remous of the temperate zone; and not on the proximity of some plateau, or elevation of the adjacent lands. The great plateaus of Asia do not stretch beyond 52° of latitude: and, iu the interior of the New Continent, all the immense basin bounded by the Alleghany range and the rocky mountains, and covered with secon dary formations, is not more than from 656 to 920 feet above thé level of the ocean, according to the levels taken in Kentucky, on the banks of the Monongahela, at Lake Erie.+ Leopold von Buch's Travels in Lapland, tom. ii. If, instead of the mean temperatures of the seasons, we consider, I do not say the days of the maxima and minima of the year, which are the ordinates of the concave and convex summits of the entire curve, but the mean temperatures of the warmest and the coldest month, the increase of the differences becomes still more perceptible. We request the reader to compare, in the following table, only the places which belong to regions bounded by the same meridians, and consequently to the same system of climate; as, for example, to the region of Eastern America to that of Western Europe and that of Eastern Asia. We must also attend to the changes of temperature produced by the monsoons in a part of the equinoctial regions, and distinguish, under the temperature zone, between the climate of the interior, or the continental climate, and that of islands and coasts, We may conclude, in general, that, for any given place in the curves which express the annual temperatures, the ordinates of the concave and convex summits differ the more from one another, as the temperatures diminish. In the New World, under 40° of latitude, we find a greater difference between the warmest and coldest months of the year than in the Old World, at Copenhagen and Stockholm, under 56°59° of latitude. At Philadelphia, the thermometer descends to 50° or 59° below the freezing-point, while, under the same parallel in Europe, it descends scarcely 30.6 below it. On high mountains in islands of little extent, and along the shores, the lines of annual temperature take nearly the same form as in warm climates, having only a less degree of curvature. The difference between the seasons, too, becomes smaller. At the North Cape, in 71° of latitude, and in the isothermal line of 32°, it is almost 11° greater than at Paris, in 49° of latitude, and in the isothermal line of 50°. The sea-breezes and the fogs which render the winters so temperate, diminish at the same time the heats of summer. The characteristic of any climate is not the difference between the winters, expressed in degrees of the thermometer: it is this difference, compared with the absolute quantities indicated by the mean temperature of the seasons. II. Difference between the Winters and Summers, in following the same Isothermal Line from West to East. The differences between the seasons of the year are less great near the convex summits of the isothermal curves, where these curves rise again towards the North Pole, than near the concave summits. The same causes which affect the inflexion or the greatest curvature of the isothermal lines, tend also to equalize the temperatures of the seasons. The whole of Europe, compared with the eastern parts of America and Asia, has an insular climate; and, upon the same isothermal tine, the summers become warmer and the winters colder, in proportion as we advance from the meridian of Mont Blanc towards the east or the west. Europe may be considered as the western prolongation of the old continent; and the western parts of all continents are not only warmer at equal latitudes than the eastern parts, but, even in the zones of equal annual temperature, the winters are more rigorous and the summers hotter on the eastern coasts than upon the western coasts of the two continents. The mean temperature of the year being equal to the fourth part of the winter, spring, summer, and autumnal temperatures, we shall have upon the same isothermal line of 53:6 (12° cent.) At the concave summit in America, 53.6 — 32° + 52·3 +75'6 + 54.5 74.40 West long. At the convex summit in Europe, 2.20 West long. At the concave summit in Asia, 116 20 East long. } 53.6= 53.6 = 4 40·1 +51·8+ 68·4 + 54·1 4 -248+547 + 80·6 +54′3 4 This analogy between the eastern coasts of Asia and America sufficiently proves that the inequalities of the seasons, of which we have endeavoured to fix the numerical relations, depend on the prolongation and enlargement of continents towards the pole; of the size of seas in relation to their coasts; and on the frequency of the N.W. winds, which are the vents de Remous of the temperate zone; and not on the proximity of some plateau, or elevation of the adjacent lands. The great plateaus of Asia do not stretch beyond 52° of latitude; and, iu the interior of the New Continent, all the immense basin bounded by the Alleghany range and the rocky mountains, and covered with secon dary formations, is not more than from 656 to 920 feet above the level of the ocean, according to the levels taken in Kentucky, on the banks of the Monongahela, at Lake Erie.+ • Leopold von Buch's Travels in Lapland, tom. ii. |