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CLIMATE. 155

intch affects the climate, and as a general rule the western sides of continents and large islands, are warmer than the eastern. Certain portions of the globe, which from their nearness to the equator would be extremely warm, are rendered tolerably cool by their elevated situations. This is the case with much of the tropical land in America, which is so raised that it rivals even European climates in mildness and agreeable temperature. The air of these elevated tropical districts is remarkably pure and transparent, and the winds which sweep over the plains, are cooled by their passage down the snow-capped mountains, which rear their bright summits to the skies. The vast expanse of table-land, forming the empire of Mexico is of this character, being elevated 7000 feet above the level of the ocean. This land in many parts has the fertility of a cultivated garden. The plains of Columbia in South America, and indeed all along the ridge of the Andes, are similarly situated. The chart which we have given represents the direction of the isothermal lines, or lines connecting places which have the same mean annual heat. It will be evident that places may thus be situated on the same isothermal line, which have very unequal mean temperatures of summer and winter. We need only refer to the table on page 157, to be convinced of this. Thus, the mean annual temperature of London, and Cambridge, Mass, is the same, 50°36'; but the mean temperature o the warmest month at London is 64°40', while at Cambridge it is 72°86', and of the coldest month, at London 37°76, at Cambridge 29.84, London therefore has a colder summer and a warmer winter than Cambridge. The reason of this, is undoubtedly, the insular situation of the former, for as a general rule the extremes of temperature are experienced in large inland tracts, and little felt in islands remote from continents. The difference between the mean temperature of summer and winter is nothing at the equator, and increases continually with the latitude. When the mean annual temperature is low the difierences between the 'extremes of the seasons is great, and the contrary.

The effect of climate upon the geographical distribution of plants and animals is very marked. Each, generally has its pe

culiar climate where it thrives best, and beyond certain limits it ceases to exist. The successive zones of vegetation, as we recede from the equatorial regions, have sometimes been supposed to be represented by the different altitudes upon the mountains under the equator, as it is evident we have in ascending from the valleys to their snow-capped summits, every variety of temperature. The analogy fails however in one essential point, for as we ascend the mountains the pressure of the atmosphere is continually diminished and it is evident that less nutriment is thus afforded for the growth of the plant. The influence which the variations of climate alluded to, must have upon vegetation is very evident, thus in many parts of Siberia, wheat and rye are raised upon a soil which is constantly frozen at a depth of three feet, while in Iceland, where the mean temperature of the year is much warmer, and the winter's cold but inconsiderable, it is not possible to raise any of the ceralia or common grains, as the low summer temperature does not suffer them to ripen. It is for the same reason that the vine does not flourish in England, for although it can endure a tolerably great degree of cold, yet it requires a hot summer to make the fruit ripen, and yield a drinkable wine. There is no subject connected with meteorology which requires a more careful, and studied investigation than that of climates. So many causes influence the temperature of the air, and some of them are so variable, that no labor short of a well conducted series of observations, extending through a long course of years can give a satisfactory result. In the brief account we have given, we have been able to present little else than the leading facts, and must refer the reader to the writings of Leslie, De Candolle, Mirbel, and Humbolt, for further information.

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Exhibiting the mean temperature of various places compiled principally from the observations of Baron Alez. Von Humboldt.

Isother- Position. Mean mal Names of Places. |tempera| Bands. ture of o __|the Year. Lat Long. Hght. O 1 O I Feet o o' |Melville Island.......... 74 47|110 48w. 0– 2.00 * ain ...................|57 8 61 20w. 0+26. s |Enontekies.............. 68 30, 20 47E. 1356. 26.9 o Hospice de St. Gothard...46 30 8 23E. 6390. 30. 3. North Cape .............71 0 25 50E. || 0 32. a Ulea ...................65 3| 25 26E. 0| 35.0 & Umea ..................[63 50120 16E. U 33.26 * |St. Petersburg ...........59 56|30 19k. || 0 38. | 5 |Prontheim .............63 24 10 22. Q 39.9 | 3 |Moscow ................|5545, 37 32E. 970 40.1 ................ ...60 27 22 18k. 0 Upsal ..................|59 51] 17 38E. 0 . Stockholm ..............|59 20 18 3E. 0 Quebec.................)46 47 71 0w. 0 Christiania..............|59 55 10 48E. 0 of Convent of Peissenberg 47 47 10 34E. 3066 § Copenhagen ............|5541 12 35E. 0 & Kendal .................|54 17, 2 46w. 0 3 |Falkland Islands.........[5] 25, 59 59W. 0 § |Prague ........... .50 5 14 24E. 0 # 90ttingen... .......|51 32 9 53E. 456 5 |Zurich .................|47 22 8 32E. 1350 of Edinburgh ..............|55 57 3 10w. 150 3 Warsaw ............... . 52 14, 21 2E. 0 § |Coire...................46 50 930E. 1876 Dublin .... ............ .53 21 6 19w.| 0 Berne . . . . . . . . . . . . . . . . . . 46 5. 7 26E. 1650 Geneva.................|46 12 6 8E. 1080 Manheim...............)49 29| 8 28E. 432 Vienna .................|48 12, 16 22E. 420

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Isother- Position. | Mean mal Names of Places. temperaBands. ture of _____the Year. Kat. Long. Hght. O 1 || O || ||Feet O Clermont...............|45 46 3 5E. 1260 50.00 Buda... . . . . . . . . . .......|47. 29 19 le. 494 51.08 . Cambridge, Mass......... 42 22 71 Tw. 0 50.36 g. Paris...................H.8 50 2 20. 222, 51.08 § London.................5i 30| 0 5w. O 50.36 3 Dunkirk................ 31 2. 2 22E. 0. 50.54 2 Amsterdam ... . . . . . . . . . .5222 4 50E. 0. 51.62 * Brussels ................|50 50 4 22E. 0. 51.80 # Franeker . . . . . . - - - - - - - - - 52 36|| 6 22E. 0. 51.80 & Philadelphia.............|39 56 75 10w. 0 53.42 To New York ..............|40 40| 7358w. 0. 53.78 3 |Cincinnati ..............!39 6, 84 27 w. 510, 53.78 * St. Malo ................]48 39| 2 1 w! 0. 54.14 Nantes ... . . . . . . . . . . . . . .47 13 1 32w. Q 54.68 Peking . . . . . . . . . . . . . . . . .39 54116 27E. 0. 54.86 Milan ....... . . . . . . . . . . .45 28, 9 11E. 390 55.76 | Bordeaux . . . . . . . . . . . . . . .44 50| 0 34w. 0. 56.48 Marseilles...............A. 17 § 23. Q 33:00 5 o' Montpellier .............|43 36 .352k. Q. 53.36 & 3 Rome . . . . . . . . . . . . . . . . . .41 53| 12 27E. 0 60.44 Too Toulon ... . . . . . . . . . . . . . .43 7 5 50E. 0, 62.06 ## Nangasaki .............. 32 45||129 55E. 0 60.80 * Natchez ................ 31 34 91 24W.; 180 64.76 68° to Funchal . . . . . . . . . . . . . . . . [32 37' 16 56w. 0| 68.54 72°. Algiers . . . . . . . . . . . . . . . . .3648] 3 le. 0| 69.98 co Cairo...................!30 2. 30 18E. 0 72.32 ##3. Vera Cruz ..............|19 11! 96 lw. 0 77.72 ###|Havana.................23 10| 82 13W. Q. 1803 Cumana .... .... .......]10 27| 65 15w. 0| 81.86

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“Why do those cliffs of shadowy tint, appear
More sweet than all the landscape smiling near 7
'Tis distance lends enchantment to the view,
And robes the mountain in its azure hue.”
Campbell.

In the present chapter we shall describe and explain the general optical appearance of the sky, and some of the more striking optical phenomena connected with our present subject. When the rays of the sun strike the minute particles of air, which, according to circumstances, may be more or less dense, or charged with watery vapor, they are either reflected, or transmitted; in either case sometimes returning the most beautiful colors. It is a fact to well known to need much illustration from us, that light, whenever it is refracted by any medium, such as glass or water, is al-, ways separated into the prismatic colors, whenever the surfaces of the medium are curved, or inclined to each other. It is not however, so generally understood, that these different colored rays have different powers of penetrating through various media, and that they move with different velocities. This however, is susceptible of demonstration, and it is to this that the beautiful colors of an autumnal sunset are owing. The red, violet and orange rays have the greatest velocity, and penetrate the thick dense strata of horizontal air, with the greatest facility, giving us the rich and brilliant hues of sunset and sunrise, tinging the morning and evening clouds with glowing red, and gold; and the sobertwilight,with that purple fading into gray which is assumed when the ruddy glare of sunset is tempered by the azure of the sky. Since the red and yellow rays which compose white light, are transmitted by the air, unattended by the blue fays, it follows that these latter must be reflected, hence the beautiful

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