It is only the girdling, encircling air that flows above and around all that makes the whole world kin. The carbonic acid with which to-day our breathing fills the air, to-morrow makes its way round the world. The date-trees that grow round the falls of the Nile will drink it in by their leaves; the cedars of Lebanon will take of it to add to their stature; the cocoa-nuts of Tahiti will grow rapidly upon it; and the palms and bananas of Japan will change it into flowers. The oxygen we are breathing was distilled for us some short time ago by the magnolias of the Susquehanna; the great trees that skirt the Orinoco and the Amazon, the giant rhododendrons of the Himalayas, contributed to it, and the roses and myrtles of Cashmere, the cinnamon-tree of Ceylon, and the forest, older than the Flood, buried deep in the heart of Africa, far behind the Mountains of the Moon. The rain we see descending was thawed for us out of the icebergs which have watched the polar star for ages; and the lotus-lilies have soaked up from the Nile, and exhaled as vapour, snows that rested on the summits of the Alps.—North-British Review.
THE HEIGHT OF THE ATMOSPHERE.
The differences existing between that which appertains to the air of heaven (the realms of universal space) and that which belongs to the strata of our terrestrial atmosphere are very striking. It is not possible, as well-attested facts prove, perfectly to explain the operations at work in the much-contested upper boundaries of our atmosphere. The extraordinary lightness of whole nights in the year 1831, during which small print might be read at midnight in the latitudes of Italy and the north of Germany, is a fact directly at variance with all we know according to the researches on the crepuscular theory and the height of the atmosphere. The phenomena of light depend upon conditions still less understood; and their variability at twilight, as well as in the zodiacal light, excite our astonishment. Yet the atmosphere which surrounds the earth is not thicker in proportion to the bulk of our globe than the line of a circle two inches in diameter when compared with the space which it encloses, or the down on the skin of a peach in comparison with the fruit inside.
COLOURS OF THE ATMOSPHERE.
Pure air is blue, because, according to Newton, the molecules of the air have the thickness necessary to reflect blue rays. When the sky is not perfectly pure, and the atmosphere is blended with perceptible vapours, the diffused light is mixed with a large proportion of white. As the moon is yellow, the blue of the air assumes somewhat of a greenish tinge, or, in other words, becomes blended with yellow.—Letter from Arago to Humboldt; Cosmos, vol. iii.
BEAUTY OF TWILIGHT.
This phenomenon is caused by the refraction of solar light enabling it to diffuse itself gradually over our hemisphere, obscured by the shades of night, long before the sun appears, even when that luminary is eighteen degrees below our horizon. It is towards the poles that this reflected splendour of the great luminary is longest visible, often changing the whole of the night into a magic day, of which the inhabitants of southern Europe can form no adequate conception.
HOW PASCAL WEIGHED THE ATMOSPHERE.
Pascal’s treatise on the weight of the whole mass of air forms the basis of the modern science of Pneumatics. In order to prove that the mass of air presses by its weight on all the bodies which it surrounds, and also that it is elastic and compressible, he carried a balloon, half-filled with air, to the top of the Puy de Dome, a mountain about 500 toises above Clermont, in Auvergne. It gradually inflated itself as it ascended, and when it reached the summit it was quite full, and swollen as if fresh air had been blown into it; or, what is the same thing, it swelled in proportion as the weight of the column of air which pressed upon it was diminished. When again brought down it became more and more flaccid, and when it reached the bottom it resumed its original condition. In the nine chapters of which the treatise consists, Pascal shows that all the phenomena and effects hitherto ascribed to the horror of a vacuum arise from the weight of the mass of air; and after explaining the variable pressure of the atmosphere in different localities and in its different states, and the rise of water in pumps, he calculates that the whole mass of air round our globe weighs 8,983,889,440,000,000,000 French pounds.—North-British Review, No. 2.
It seems probable, from many indications, that the greatest height at which visible clouds ever exist does not exceed ten miles; at which height the density of the air is about an eighth part of what it is at the level of the sea.—Sir John Herschel.