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rise to currents, interrupted, however, by the presence of masses of clouds, and even by the effects of their own shadows. · The influence of plains, on the other hand, depends on the equality of their surfaces, their extent, the presence or absence of vegetation, and their juxtaposition in steppes. Humboldt found, by direct observation, that in the Cordilleras of the Andes, between the tropics, plains having the trifling extent of 25 square leagues, raise the mean temperature of the air from 20.7 to 4o.2 Fahr. above that which is found at an equal elevation on the steep sides of mountains.p. 529.

It is important to observe that the snow line must not be con-founded with an isothermal curve, that is to say, a curve of equal annual temperature. It indicates neither the stratum of air of which the temperature is at the point of congelation, nor that of any stratum of air whatever, having an equal mean temperature. Under the equator, in the plain of Quito, the snow line corresponds with the atmospheric stratum whose mean temperature is 34o.7, while at the polar circle its elevation corresponds to a temperature of only 20°. Hence it appears that the altitude of the snow line is not, in the language of mathematicians, a function of the mean temperature of the year alone; it depends also on the distribution of the annual heat through the different seasons, and on the duration and mean temperature of the summer. As we proceed from the equator towards the pole, its altitude decreases more rapidly than that of the line which indicates the mean temperature of the hottest months, but much more slowly than if it depended solely on the mean temperature of the whole year.

The altitude of the snow line on the different ranges of mountains in Asia has been hitherto very imperfectly determined; but in a general view, it may be regarded as very considerably greater than in Europe, or even America, under the same parallel of latitude. From the report made to the Imperial Academy of Sciences of Petersburg, of a journey to the summit of mount Elbrouz, by MM. Kupfer and Lenz, in 1829, it appears that the limit of perpetual snow on that mountain is elevated to the height of 11,000 English feet, while, in the Pyrenees, under the same latitude, its elevation, according to the observations of Ramond, is only 8,690 feet, so that it is 2,300 feet higher in the Caucasus than in the Pyrenees. The great influence of local circumstances on the position of the snow line is strikingly exemplified by the phenomena of the Himalaya range. the southern side of this immense chain, towards Hindostan, under the latitude of 30° or 31°, the snow line is at an elevation of 12,400 feet; but on the side towards Thibet, snow disappears in summer, even at the enormous elevation of 16,600 feet. This

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remarkable difference of 4,200 feet, which was first made known by Captain Webb, in 1816, is ascribed by Humboldt to the powerful radiation which takes place in summer from the elevated plains of Thibet, to the small quantity of snow that falls in winter, when the temperature sinks below 10° of Fahrenheit, and to the serenity and clearness of the atmosphere on the northern side of the Himalaya ;-circumstances which at the same time increase the radiation from the plains, and facilitate the transmission of the heat to the colder regions.

The mean temperature of the equatorial zone is as yet very imperfectly determined; but Humboldt thinks it does not exceed 80° of Fahrenheit. The greatest summer heats are found in countries contiguous to the tropics. On the Red Sea, for example, the thermometer is often seen to rise to 110° at mid day, and to remain at 94o during the night. In the production of this extreme heat, astronomical causes combine their influence with the local peculiarities of the circumjacent countries. A few degrees within the tropic, the sun at midsummer continues for a considerable space of time to pass daily very near the zenith; and the day, increasing with the latitude, 'is longer than under the equator, so that the amount of nocturnal radiation is diminished. Among the local causes which contribute to give an excessive climate to the Arabian peninsula and the tropical countries of Africa, we may reckon the sandy surface, almost entirely deprived of vegetation, the constant dryness of the air, the direction of the winds, and the quantity of heat radiated from earthy particles carried about in the atmosphere.

We shall not attempt to follow M. Humboldt through his last Memoir-On the Causes of the Inflexion of the Isothermal Lines -more especially as it contains few facts of any importance which were not already stated in his former essays in the Memoires d'Arcueil and Annales de Chimie, and with which the public are in consequence already acquainted.

The last subject to which we shall advert is one of great geognostical interest, and which has excited much controversy,we allude to the discovery in the frozen plains of Siberia, of the carcases of animals belonging to species that are now found only in tropical regions, in a state of almost entire preservation. Cuvier was of opinion that this extraordinary circumstance could not be explained without supposing some instantaneous cause of cooling, such as would result from a sudden and violent change of the axis of the earth's rotation; for it is impossible to suppose that the skin and flesh of an entire carcase, such as that found by Mr. Adams, could have been preserved from corruption, unless it had been instantaneously en

VOL. X. NO, XIX,

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veloped in the ice in which it was found; and thus, says Cuvier, every hypothesis which involves a gradual cooling of the earth, or a gradual change in the position of its equator, falls of itself. Humboldt thinks the true explanation of the phenomenon is to be found in the frozen state of the earth, under high latitudes, at the depth of five or six feet below the surface; but we cannot regard his reasoning on this subject as altogether conclusive and satisfactory. The existence of thick strata of ice, or rather of frozen earth, is, however, an incontestable fact, supported by numerous observations, and in itself of no little importance to geology. In the months of July and August, when the temperature of the air rose to 86°, Humboldt found between the convent of Abalak and the city of Tara, in latitudes corresponding to Scotland and the north of England, namely, between 561° and 58°, some springs of no great depth, the temperature of which was only 34°. 7 and 360,5. Some degrees to the north of Irkoutsk, or about the latitude of 69°, where the mean temperature of the year is between two and three degrees below the freezing point, the soil remains always frozen to the depth of twelve or fifteen feet. At Bogoslowsk, in the middle of summer, a bed of frozen earth, nine and a half feet thick, was found at the depth of six feet under the surface; and at Jakoutsk, 41° to the south of the polar circle, notwithstanding the high temperature of the air in the months of July and August, the subterranean ice is a "general and perpetual phenomenon." It is easy to suppose that between Jakoutsk and the mouths of the Lena, froin 620 to 72° of latitude, the thickness of the congealed stratum must rapidly increase.

Now if we can only admit the existence in high latitudes of animals corresponding to those whose fossil remains are now so plentifully found, these capacious beds of everlasting ice will enable us to account for the phenomena of their preservation. Humboldt thinks their existence, even in the actual state of the system of Asiatic climates, to be by no means improbable, and in support

of this opinion cites the example of the royal tiger of Bengal. This animal, which we are accustomed to consider as belonging to a tropical country, is at the present day frequently met with in Siberia, even as far north as the parallels of Berlin and Hamburg. Individuals of the tribe live, beyond all dispute, on the northern side of the Thian-chan, or Celestial Mountains; on the steppe of the Kirghiz and the banks of the Upper Irtyche; and they make excursions even to the western declivity of the Altai, between Boukhtarminsk, Bernaoul, and the celebrated silver mine of Schlangenberg, where many of them have been killed of an enormous size. But what is at present true of the royal tiger may have been formerly true of the elephant and rhi

If then we suppose that in one of the last revolutions which the earth has undergone, for example, in the upraising of a recent chain of mountains, like the Oural, elephants and other species had fled beyond their usual haunts to the banks of the Vilhoui and the mouths of the Lena, numerous accidents might bring their carcases in contact with the frozen strata always existing a few feet under the surface, and in this case they would be safely preserved from putrefaction,

noceros.

This hypothesis relieves us from the necessity of supposing that any great change of temperature has ever taken place at the surface of the earth; but it is hardly possible to believe, in the face of numerous geological facts, that the climatology of the ancient continent has not undergone at least a very great modification. No one, we think, who takes the trouble to read the luminous exposition of facts given by Mr. Lyell in the first volume of his excellent work on geology, will pretend to doubt that a great alteration of climate in the northern hemisphere has been fully established. Part of the effect may be, and most probably is, owing to a change of conformation, arising from the elevation of mountains, or of insular or continental masses from the bottom of the sea by the action of subterraneous forces; but much of it may also, we think, be ascribed to the diminution of the quantity of internal heat communicated to the atmosphere through crevices in the oxydized crust of the earth.

We cannot conclude our account of these Memoirs, without expressing the satisfaction we have in believing that, owing to the zeal with which the natural and physical sciences are at present cultivated among the Russians, the great want of positive information respecting the geography, natural history, and climate of Asia, under which science still labours, will soon be removed. During his recent expedition Humboldt left a number of thermometers in various parts of Siberia, in the hands of persons capable of making excellent use of them, and many valuable results have already been communicated. The Academy of St. Petersburg, also, with that spirit which it uniformly displays when the interests of science are concerned, has adopted the design of causing a regular series of simultaneous observations to be made, over the whole extent of the Russian empire,-of the diurnal variations of the barometer, thermometer, and hygrometer-of the temperature of the earth,--the direction of the winds, and the quantity of rain and snow deposited by the atmosphere. If this design is carried into execution, the laws which regulate the distribution of heat over the terrestrial surface will become better known to us than they have hitherto been, and Climatology be raised to a higher position among the accurate sciences than it at present occupies.

It con

Art. III.-Opinion de M. Cristophe, deuxieme partie; suivie de

son voyage, commerciale et philosophique. Par M. Boucher de

Perthes. Sm. 8vo. Paris. 1831. In our last number we gave an account of the measures adopted within the last few years affecting our Navigation Laws and Colonial system, and of what is called the “ Reciprocity” arrangement. We now propose to pursue a similar inquiry into that branch of the “ New System,” which has acquired the popular but inaccurate designation of “ Free Trade." It has been already shown that the “ Reciprocity" and the “ Free Trade, " though often confounded, are things perfectly distinct. Either might exist without the other. The first is essentially an arrangement in which foreign powers are directly concerned, which varies according to the conduct of each foreign power, and has, in fact, been the subject of stipulation with most of them. sists in treaties of Commercial Peace. The second only indirectly concerns foreign countries; it is not adjusted with reference to their conduct, and has not been the subject of any of the recent treaties. While, therefore, we are in many cases restrained by stipulation from imposing a duty upon importations in foreign vessels, as being in such vessels, we have within our own power the arrangement of our duties upon merchandize of all sorts, imported or exported; with full competence to augment to any extent the duties on foreign articles, because they are foreign; provided only, that we do not favor the produce of one country more than that of another, with which we have made the stipulation to treat, and be treated, as the “ most favoured vation.”

The two branches of the new system are not less distinct in practice than in law. Our duties upon foreign goods imported have not been arranged with any reference to the existence, or non-existence, of a reciprocity treaty: it has happened that we have favored, by our application of the system of free trade, the goods of a country, with which we have been engaged in a contest as to the reciprocity in regard to ships ;* and it has also bappened that we have renewed a reciprocity treaty with a nation, with which we have been at the same time engaged in a contest as to the duties on goods.

It is thus a great mistake to consider the new measures affecting the duties on silk, iron, and most manufactured articles, which measures constitute what is not very accurately called the system

• France.-We admitted French silks, while we imposed a retaliatory duty on French ships under the order of 10th March, 1894.

† The United States of America.

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