THE AIR-OCEAN.

ENVELOPING this solid globe of ours are two oceans, one partial, the other universal. There is the ocean of water, which has settled down into all the depressions of the earth's surface, leaving dry above it all the high lands, as mountain ranges, continents, and islands; and there is an ocean of air, which inwraps the whole in one transparent mantle. Through the bosom of that ocean, like fishes with their fins and whales with their flippers, birds and other winged creatures swim; whilst, like crabs and many shell-fish, man and other mammalia creep about at the bottom of this aerial sea.

The air-ocean, which everywhere surrounds the earth, and feeds and nourishes it, is even more simple, more grand, and more majestic, than the "world of waters;" more varied and changeful in its moods of storm and calm, of ebb and flow, of brightness and gloom. The atmosphere, is indeed, a wonderful thing, a most perfect example of the economy of nature. Deprived of air, no animal would live, no plant would grow, no flame would burn, no light would be diffused. The air, too, is the sole medium of sound. Without it, mountains might fall, but it would be in perfect silence-neither whisper nor thunders would ever be heard. The atmosphere is supposed to extend from the earth to a height of between forty and fifty miles.

A philosopher of the East, with a richness of imagery truly Oriental, thus describes it :-" It surrounds us on all sides, yet we see it not; it presses on us with a load of fifteen pounds on every square inch of surface of our bodies, or from seventy to one hundred tons on us in all, yet we do not so much as feel its weight. Softer than the softest down, more impalpable than the finest gossamer, it leaves the cobweb undisturbed, and scarcely stirs the lightest flower that feeds on the dew it supplies; yet it bears the fleets of nations on its wings around the world, and crushes the most refractory substances with its weight. When in motion, its force is sufficient to level the most stately forests and stable buildings with the earth-to raise the waters of the ocean into ridges like moun

tains, and dash the strongest ships to pieces like toys. It warms and cools by turns the earth and the living creatures that inhabit it. It draws up vapours from the sea and land, retains them dissolved in itself, or suspended in cisterns of clouds, and throws them down again as rain or dew when they are required. It bends the rays of the sun from their path, to give us the twilight of evening and of dawn; it disperses and refracts their various tints to beautify the approach and the retreat of the orb of day. But for the atmosphere, sunshine would burst on us and fail us at once, and at once remove us from midnight darkness to the blaze of noon. We should have no twilight to soften and beautify the landscape; no clouds to shade us from the scorching heat, but the bald earth, as it revolved on its axis, would turn its tanned and weakened front to the full and unmitigated rays of the lord of day. It affords the gas which vivifies and warms our frames, and receives into itself that which has been polluted by use, and is thrown off as noxious. It feeds the flame of life exactly as it does that of the fire;-it is in both cases consumed, and affords the food of consumption; in both cases it becomes combined with charcoal, which requires it for combustion, and is removed by it when this is over."

"It is only the girdling, encircling air," says another philosopher, "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 seeks its way round the world. The datetrees that grow around 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, and 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. 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."

"The atmosphere which forms the outer surface of the habitable world is a vast reservoir, into which the supply of food designed for living creatures is thrown; or, in one word, it is itself the food, in its simple form, of all living creatures. The animal grinds down the fibre and the tissue of the plant, and the nutritious store that has been laid up within its cells, and converts these into the substance of which its own organs are composed. The plant acquires the organs and nutritious store thus yielded up as food to the animal, from the air surrounding it."

"But animals are furnished with the means of locomotion and of seizure-they can approach their food, and lay hold of and swallow it; plants must wait till their food comes to them. No solid particles find access to their frames; the restless ambient air, which rushes past them loaded with the carbon, the hydrogen, the oxygen, the water, everything they need in the shape of supplies, is constantly at hand to minister to their wants, not only to afford them food in due season, but in the shape and fashion in which alone it can avail them."

There is no employment more ennobling to man and his intellect than to trace the evidences of design and purpose in the Creator, which are visible in all parts of the creation. Hence, to him who studies the physical relations of earth, sea, and air, the atmosphere is something more than a shoreless ocean, at the bottom of which he creeps along. It is an envelope or covering for the dispersion of light and heat over the surface of the earth; it is a sewer into which with every breath we draw we cast vast quantities of dead animal matter; it is a laboratory for purification, in which that matter is recompounded and wrought again into wholesome and healthful shapes; it is a machine for pumping up all the rivers from the sea, and conveying the waters from their fountains in the ocean to their sources in the mountains; it is an inexhaustible magazine, marvellously adapted for benign and beneficent purposes.

MAURY.

and nitrogen.

acid gas.

WHAT IS AIR?

THE atmosphere is composed principally of two gases, oxygen It contains also a small but variable proportion of watery vapour, and a still smaller proportion of carbonic The leading characteristics of oxygen are, that it is the supporter of combustion, as fire will not burn without its presence; and it is also the life-sustaining element in the air we breathe. When a piece of charcoal, which is pure carbon, is burned in the open air, the combustion consists in the union of the carbon of the charcoal with the oxygen of the air, forming the compound, carbonic acid. When wood is burned, the process and the result are the same, with the exception that the wood is not wholly carbon, and the other ingredients appear during the combustion in the form of smoke and ashes. The rusting of metals is a slow combustion, termed oxydation; and whenever oxygen unites with any other element, some degree of heat is evolved in the process.

Iron and other metals burn with exceeding brilliancy in oxygen gas; and, what is more strange, the most intense heat known is produced by burning oxygen and hydrogen in the proportions which form water. Although no two things in nature are more opposite in character than fire and water, yet in this burning process the water is the product of the fire! Oxygen is heavier than common air, and may be poured from one vessel into another; yet it is invisible, inodorous, and tasteless, and can be detected only by its effects upon other bodies.

The other constituent of the atmosphere, nitrogen, or azote, is as inert in its properties as oxygen is active. In nitrogen no animal can live, no flame can burn; and its principal use in the atmosphere seems to be to dilute the oxygen, and subdue this wonderfully active being to the endless number of useful purposes required in the economy of nature. Every particle of oxygen in the atmosphere is accompanied by four particles of nitrogen; or, in other words, if we take a measure of any capacity full of atmospheric air, and divide it into five parts, the nitrogen will occupy

four parts, and the oxygen only one part: it is, however, an important and wonderful property of gases to mingle together so intimately, that, although oxygen is heavier than nitrogen, both these gases will be diffused through every part of the vessel; and it is the same everywhere on the grand scale of nature.

Carbonic acid exists in the air in a very small proportion. At ordinary elevations there are only about two gallons of this gas in every 5,000 of air. It increases, however, as we ascend, so that at heights of 8,000 or 10,000 feet the proportion of carbonic acid is nearly doubled. Even this increased quantity is very small; and yet its presence is essential to the existence of vegetable life on the surface of the earth. But, being heavier than common air, it appears singular that the proportion of this gas should increase as we ascend into the atmosphere. Its natural tendency would seem to be rather to sink towards the earth, and there to form a layer of deadly air, in which neither animal nor plant could live. But, independent of winds and aërial currents, which tend to mix and blend together the different gases of which the air consists, all gases, by a law of nature, tend to diffuse themselves through each other, and to intermix more or less speedily, even where the utmost stillness prevails and no wind agitates them.

The purposes which we know to be served by these several constituents of the atmosphere show both that they are all essential to the composition of the air, and that, in quantity as well as kind, they have been beneficently adjusted to the composition, the wants, and the functions of animals and of plants.

Thus, as to the oxygen

From every breath of air which the animal draws into its lungs it extracts a quantity of oxygen. The oxygen thus obtained is a part of the natural food of the animal, which it can obtain from no other source, and new supplies of which are necessary to it every moment. The oxygen of the atmosphere, therefore, is essential to the very existence of life in the higher orders of animals. The candle burns, also, and all combustible bodies kindle in the

air, only because it contains oxygen. This gas is a kind of necessary food to flaming and burning bodies; so that, were it absent