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at the end of which the new and full moons happen on the same days of the year as they did at the beginning, is very remarkable, for by it Christians have always ascertained the days of their movable festivals, and the Greeks adopted it for the like purpose in 433 B.C., Meton having obtained the first prize at the Olympic games for its discovery. Now Meton may have derived it through Hecatæus from Britain, as above-mentioned, and the British Druids may have had it from the Jews, whose year in the time of Moses consisted, like our own, of 365 days, and whose great festival of the Passover was (like ours of Easter) regulated by the moon. It is, I imagine, to this cycle of nineteen years that the number 19, so prominent in our Druidical temples, refers.

On the Constitution of the Atmosphere. By M. LEWY. Read to the French Academy of Sciences.

The memoir which I have the honour to submit to the Academy contains the results of a series of researches on the constitution of the atmosphere, executed between France and New Granada, and from the coast up to 3193 metres above the level of the sea.

The analyses were performed by the new process of M. M. Regnault and Reiset, which consists, as is well known, in analysing the air by volumes. To measure the elastic forces of the gas I employed an excellent cathetometer, constructed by M. Perraux. The process thus combined enables us to obtain much greater precision than has hitherto been reached in this class of experiments. To judge of the degree of accuracy attainable, it suffices to examine the numerical details of two analyses; and it will be seen that the greatest difference between two analyses made with the same specimen of air never exceeded 1,0th, and most frequently was not more than roo,booth.

The various specimens of air which I analysed were collected in bulb tubes with the two ends drawn out and open; the capacity of these tubes was about 100 cub. centims. The air was collected in the following manner: one of the extremities of the tube was connected by means of caoutchouc

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.

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

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