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tubing, with a little pair of bellows, which was moved sufficiently long to be certain that the whole of the air contained in the tube was replaced by the atmospheric air of the locality, taking the necessary precautions to avoid any mixture of the air of respiration; as soon as the air was collected the tubes were sealed before the lamp.

I have divided the analyses into three series: 1st, Analysis of the atmospheric air of France; 2d, Analysis of the atmospheric air of the Atlantic Ocean and Carribean Sea; 3d, Analysis of the air of New Granada.

The comparison of the results obtained in this investigation with previous ones shows that the constitution of the atmosphere is nearly the same in the New World and the Old World. Taking the mean of the analyses, executed in eleven different localities of New Granada, we find that 10,000 vols. of normal atmospheric air contain 4.008 carbonic acid, 2101 425 oxygen, and 7894-557 azote, which are nearly the same proportions as those which have been found for normal atmospheric air in various parts of Europe. However, on examining carefully all the experiments hitherto made on the constitution of the atmosphere, it is readily seen that the composition of the air is not absolutely constant. Perceptible differences exist, which vary with the meteorological conditions; thus after a long rain the carbonic acid and oxygen are always in smaller proportion than after a long drought; however, these differences are only appreciable when the analysis has been carried out with very great accuracy.

In the New World, where the seasons are more defined than in Europe, these variations are more easily detected. During the fine season the normal air always contains a little more oxygen and a little more carbonic acid than in the season of the rains. Thus taking the mean of a large number of analyses, I found that 10,000 vols. of normal atmospheric air of Bogota contain:

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The difference which exists between the atmospheric air of the two seasons is therefore on an average 0.751 for the carbonic acid, and 2-653 for the oxygen in 10,000 vols. of

air.

Taking the maximum and minimum of the results obtained in the analyses performed during the two seasons, we have,

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Volumes, 10,000.000 Volumes, 10,000.000

The greatest difference amounts consequently to 1.434 for the carbonic acid, and to 4-167 for the oxygen. These differences are nearly the same as those which I found between the atmospheric air of Paris and that of Havre, analysed under meteorological conditions corresponding to the two seasons of South America.

It follows that the composition of the air which we breathe is the same in Europe and in the New World as far as regards the oxygen and the azote, whether it be taken at the level of the sea, or at an elevation of 3000 metres; the only difference is the amount of carbonic acid, which appears, especially on the high mountains, to be somewhat greater than in the valleys, and on the sea-shore.

With respect to the analyses of the air collected on the ocean, they have yielded a very interesting result. In the day-time this air constantly contains a little more oxygen, and a little more carbonic acid, than during the night. This difference becomes more perceptible as we leave the coasts; and it is probably owing to the solar rays, which, heating the surface of the sea during the day, disengage a portion of the gases which the sea-water holds in solution, and which, as is well known, contains more oxygen and carbonic acid. than atmospheric air.

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Taking for term of comparison the specimens of atmospheric air collected on the Atlantic, on the same day, with the same wind, and at more than 400 leagues distant from land, we find :—

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The difference is therefore 2.074 for the carbonic acid, and 9-960 for the oxygen in 10,000 volumes of air.

The analyses of the abnormal air of New Granada present us with results not less interesting. From time to time, once or twice in the year, the atmosphere of New Granada contains an extraordinary proportion of carbonic acid, which coincides with an appreciable decrease of oxygen; and, consequently, alters the constitution of the atmosphere in a very marked manner.

The great number of volcanoes which exist in the New World, and the clearing of forests which are effected every year in this country, may cause these alterations. It is, in fact, during these clearances that the constitution of the atmosphere experiences the extraordinary changes which I have just mentioned.

These clearings which are effected by vast conflagrations in the country las quemas, produce considerable quantities of carbonic acid, which, mixing with the atmosphere, alter its composition. The amount of carbonic acid which I found in this air, rose in some analyses to 49 in 10,000 volumes of air. It is consequently from 10 to 11 times greater than in the air in its normal condition. The diminution of oxygen amounted sometimes to 68.350 in 10,000 volumes of air; instead of 2101-425 oxygen, I found only 2033-075. This decrease is therefore readily detected even by less sensitive methods than the one which I employed.

On the other hand, the air of the table-land of Bogota sometimes presents an amount of carbonic acid far greater than the atmosphere of the Tierra caliente. This difference may be explained either by the existence of volcanoes, which are situated not far from Bogota, or by the more or less active influence of the solar light. It will be conceived, in fact, that in the Tierra caliente, where the temperature is very eleVOL. LII. NO. CIII.-JANUARY 1852.

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vated, the decomposition of the carbonic acid by the green parts of the vegetables must be effected in a far more rapid manner than on the high table-land of Bogota, where the temperature is not higher than from 37° to 64° Fahr.

It is perhaps allowable to suppose, on observing this enormous quantity of carbonic acid appear from time to time in the atmosphere of the New World, and considering the large number of volcanoes which exist in the country, that a portion of the carbonic acid of the air is due to them, and that they thus contribute in part to nourish the vast and beautiful vegetation of the tropics.-Comptes Rendus, Sept. 29, 1851.

M. B. Lewy's Expedition to New Granada. 1. Geology and Mineralogy, especially the remarkable discovery of the Geological Position of the Emeralds of Muzo. 2. New Animals and Plants of that Country.

The accomplished naturalist and traveller M. B. Lewy, who left Europe in 1847 for the republic of New Granada, on a natural history expedition, has returned to Europe with rich and important collections illustrative of the geology, mineralogy, botany, and zoology of that interesting part of the New World. These collections have been deposited in the Museum of the Garden of Plants in Paris. The French Academy of Sciences appointed the following commissioners to report on the collections made in New Granada by Mr Lewy, viz., MM. Duméril, Isidore Geofroy-Saint-Hilaire, Ad. Brongniart, Elie de Beaumont, Dufrénoy, Milne Edwards, Valenciennes. This report contains many important facts, some of these we shall now mention.

Geology and Mineralogy.

The rocks and specimens of minerals deposited in the Museum of the Garden of Plants were collected by Mr Lewy in the valley of the Magdalena and the eastern Cordillera. The greater number of specimens are from the north side of that chain, and others from the south side, on which is

situate, at a height of 2661 metres, Santa Fé de Bogota. Mr Lewy explored the mountainous regions to the north of that city, in the direction of Velez, de Tunja, de Muzo, &c. In ascending the course of the river Magdalena, he examined the alluvium of that river. Among the blocks rolled by the water of this river were masses of mica-slate, sienite, diorite, porphyry, sandstone, and varieties of black limestone. On the banks of the Magdalena, in other points of the valley, he observed a recent conglomerate, consolidated by a ferruginous base.

The table-land of Bogota and the mountains which vary its surface are formed of a very thick calcareous deposit, composed of numerous beds of red and white sandstone and schist, and of carburetted black limestones. These rocks had already attracted the attention of several observers, as Humboldt and Boussingault. More lately the Baron Gross observed and described with care the white sandstones which, in great masses, form the picturesque and singular escarpments of the Pont di Pandi, and also those from which is precipitated the celebrated waterfall of Tequendama.

The sandstones, whether red or white, contain no fossils, but such were found in several points in the beds of black limestone.

M. Lewy visited the fossiliferous localities where MM. Boussingault and Degenpart had already made collections which enjoy a just celebrity, and of which the species have been described by MM. de Buch and d'Orbigny. He has added many new species to those collected by his predecessors. We may mention Crioceras Lewyanus, Val. de Velez, one of the most beautiful which exists in any collection in Paris, and different species of Ammonites, d'Exogyres, of Trigonia, of Inocerama, &c.

Viewed in a general way, these fossils seem to confirm the conclusions which Buch and d'Orbigny have arrived at, by the study of the collections of MM. Boussingault and Degenpart, viz., that the great sedimentary table-land of Bogota corresponds to the lower cretaceous deposits of Europe, and particularly to that stage of those formations known under the name of Terrain Neocomien.

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