THE ATMOSPHERE, ITS NATURE, LAWS, AND GENERAL PHENOMENA. INTRODUCTION. Of all the works of creation, the most beautiful, the most wonderful, and the most useful, is the air or atmosphere, with which the surface of the earth is every where covered. Of every living thing, whether animal or vegetable, and whether that thing floats in the atmosphere, moves on the earth, adheres to its surface, swims in the ocean, or clings to the lowest bottom of that, the air is the breath of life; and, deprived of the air, the animal, or the vegetable, soon loses its vitality and its organization, ceases to be an independent being, as it were, and becomes mere matter, subject only to the law of gravitation. But while it enjoys this living and lifegiving substance, it is endowed with powers by which, in its sphere, it can counteract that universal law. The plant can shoot up with a force which is great in proportion to its quantity of matter, and the oak can build its lofty tower in the sky; the fish can dart from the depth of the ocean with amazing rapidity, and the eagle can lean motionless on the breast of the sky. Every species of organised being receives this common supporter of life' in a different way: Man, and those animals, whether of the land or the sea, whose blood is warm, draw it into the lungs in large portions, and by frequent inspirations; the insect tribes suck it in through little pores in the surface of their bodies; the fishes separate it from the water by that peculiar fibrous organisation which is termed gills; and the plants collect it by those leaves, with which they are always adorned in the warmer regions of the world, and adorned in summer in the colder. In the latter situations, the tree, during winter, undergoes a temporary death; and when those leaves, which enabled it to drink life from the surrounding air, wither and fall off, all the powers and functions of the plant are suspended until the returning season again expands the bud. Nor is it in these single and detached instances alone that the atmosphere is, as it were, the preserver of nature. These, indeed, are the instances most apt to strike the attention of man in the ruder and less informed states of society; and it may be for this reason that, in most languages, the words which denote the air, or atmosphere, are nearly synonymous with those that denote life; and nowhere is that analogy more ARTS, No. 3. F beautifully stated than by the inspired historian of the creation: "The Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul." But when, by the help of philosophy, we extend our contemplation, we discover that the atmosphere preserves the world itself, and that but for its ministry, even the sun itself might shine in vain, and that nature would be one dull and unproductive mass; and it is somewhat curious to remark, that the grand principle upon which the atmosphere performs its more mighty and extended functions, is an apparent counteracting of that law of gravitation, by which the matter of the earth is held together, and the earth and all the celestial bodies are sustained in their places, and enabled to perform their revolutions. Where the sun is vertical, the influence of its heat would soon reduce the surface of the earth to a cinder, were it not that the atmosphere throws in its kind and mitigating power; and in those regions of the world where the solar light falls low and slanting, perennial ice would bind up every thing, did not the atmosphere continually fetch heat to it from the warmer regions. As nature is constituted, too, there are few organised beings which can subsist, and, perhaps, none of the great operations of nature that can be carried on without the presence and co-operation of water. But water contains in itself no power of counteracting its own gravitation. By means of that, the whole of it would speedily get away from the land, lose itself in the ocean, and leave every thing terrestrial to die, were it not that the atmosphere is endowed with a power of calling back the descending tide, and not only pouring it in copious streams upon the summits of the highest mountains, but of making it perform important operations in the regions of the air. The phenomena of a substance, which is so universal and so indispensable in the economy of nature, must well repay the labour of every one who may have the good fortune to study them; and that human being who can remain ignorant upon such a subject can have but small claims to rationality. Nor is it in the operations of nature only that the atmosphere is thus useful; for, although it be of all substances the most easily moved, it gives stability to every thing placed upon the surface of the earth. At the common level of the earth, and in ordinary states of the weather, it presses upon every inch of surface with a weight of about 15 pounds; and thus, if it can be expelled from between any two substances, this very pressure will keep them together with no inconsiderable force. Hence the stability of the walls of buildings; hence the firmness with which a tree is rooted; hence various animals, by an apparatus which nature has given them for sucking the air from between their feet and any substance, can run up a perpendicular wall, or cross the level ceiling of a room. In this way the fly and the beetle are instances not only of the most wonderful mechanism, but of the minute ramifications into which the utility of the atmosphere runs, In its more general operations the air may be considered as the grand messenger of nature. Light is transported by it with a degree of rapidity which, for ordinary distances, is almost instantaneous; sound is transmitted by it at a slower rate indeed, but still rapid enough for any purpose of utility; perfumes are wafted by it in a minuteness of parts, and to distances which are quite incomprehensible. In short, it is the vehicle of fragrance, and music, and beauty. Again, heat and moisture are, as has been said, distributed by it; for, wherever it finds either of them in excess, it snatches up the superfluity, and by the very quality which enables it so to do, it fumes off with that superfluity to some place where it is required. If there be anything good, the atmosphere distributes it over the whole earth; and if any thing noxious happens to collect at any particular place, the atmosphere so scatters it that its deadly influence is not felt. But it is a general law of nature that these powers and substances which are the most beneficial in their tranquil and ordinary states, are the most terribly destructive when, by any means, their economy is deranged. The same element of fire, or rather the same operation of burning, which enables us to cook our food, and follow our business or our pleasure in the dark, can, when it is pent up in the earth, rend that in pieces, dash mountains out of their places, and instantly overwhelm cities beneath fathoms of molten stone; and in the same manner that atmospheric fluid, which so cheers us in the breath of spring, perfumed with ten thousand essences, and rich with all the melody of the groves, can arm itself with the terrors of the hurricane, and brush man before it as dust, and his habitation as stubble. Even in milder operations it can chill with frost, or blight with mildew, the plant which it supports, and make man, of whom it is the life, to shiver in the agonies of an ague. Hence the atmosphere ought not to be merely wondered at as an astonishing production; its properties and its appearances should be carefully studied, so that the good may be enjoyed and the bad avoided. This is the object to which every thing deserving the name of learning should tend; and no department of learning tends so strongly, or so directly to this, as that which unfolds the book of nature,-" unfolds the book of nature," did we say? The book of nature is never shut; it is only man that is blind, or will not read. The properties and phenomena of the atmosphere are so many, and so curious, that it is hardly possible to bring them within the limits to which this little sketch is restricted; but if the reader can master this, he will need no persuasion to seek for more detailed systems, neither, it is hoped, will he find much difficulty in the perusal of them. SECTION I. GENERAL PROPERTIES OF THE ATMOSPHERE. Although to our ordinary perceptions the air appears to be one simple substance, yet it has been found to consist of four or perhaps five which are totally different in their natures, and when acting singly, produce very opposite effects. These are, 1. Nitrogen gas, or azote, which in every situation forms rather more than three-fourths of the whole mass of any portion of the air by measure, rather less than this by weight, because it is the lightest of the ingredients. The proportion of nitrogen is about 78 per cent. of the bulk, or 74 per cent. of the weight. As existing in air it seems to be the mere vehicle of the more active substances, at least inanimate substances are not burned or rusted by it, and it is incapable of supporting life. From the latter circumstance it is called azote-azote, in Greek, meaning the deprivation or taking away of life. It is called nitrogen, because when it enters into a different combination with the very element that is joined in the greatest abundance with it in the atmosphere, there results a substance of very different appearance and properties, nitric acid or aquafortis, the corrosive or burning properties of which are well known. 2. Oxygen, rather heavier than nitrogen, and forming somewhat less than one-fourth of the atmosphere. This is the most active substance with which we are acquainted, and there is hardly a natural or even an artificial process that can be performed, in which it has not a share in one way or another. United to about one-third of its weight of hydrogen, another invisible fluid much lighter than common air, it forms water; combustion or the act of burning is nothing more than the union of it with some substance; animal life is supported, and in all probability animal heat entirely produced by the quantity of it which is inhaled in breathing; very many of the colouring substances used in painting are combinations of it with the different metals; all acids or substances that taste sour, whether solid or liquid, contain it as an ingredient, and, in short, it is found almost every where. Nor are there many productions of nature from which it can long be excluded. 3. Carbonic acid gas. This is a substance so much more weighty than the atmosphere, that though invisible, it can be poured from one vessel into another like water. It is fatal to animal life, and will not support burning, for if it be poured upon a lamp or candle, that candle will be extinguished more readily and silently, than if water be poured upon it; but it forms a part, and a large part, of all vegetables and most animals; and therefore the distribution of it by the atmosphere answers many important purposes in the economy of the world. 4. Aqueous vapour, or water so dispersed as to be invisible. This in average cases forms about one per cent. of the atmosphere by weight, or one and a half by bulk; but, as will be more particularly explained hereafter, the quantity of it which is contained in the atmosphere is constantly changing, and upon these changes depend the whole phenomena of dew, rain, snow, and hail. 5. Volatile effluvia-which are exhaled from various substances and by various operations,-as, odours from plants, and different gases from substances undergoing putrefaction, or other chemical changes. Some of these are more weighty than an equal bulk of the atmosphere, and thus descend by their gravity into the low places and hollows in the earth's surface; but the greater part of them are far more rare than the common atmospheric fluid, and are thus dispersed through its mass, or conveyed into its upper and lighter regions. It is not, however, necessary to detail minutely, the separate qualities of these substances, because, for the mere purpose of understanding the use of the atmosphere, as a general agent, and these changes of weather, of which it is the instrument, it is quite sufficient to consider it as one substance. Taking it in this one point of view, the first thing that strikes one is the peculiarity of its constitution. The different parts of it have no cohesion whatever, that is, they do not stick together, so as to require any effort to cut them asunder; and yet the pressure of the whole when put into forcible motion is sufficient not only to impede the progress of light bodies and even to drive them before it, but to overturn buildings and tear up trees by the roots. The ease with which all the parts of the air move in every direction, upwards, downwards, or laterally, enables it to insinuate itself into every hole and crevice, and thus to give stability to every substance. This property is called mobility; and it is taken as the general characteristic of one of the three forms in which matter exists. These forms are solids, which adhere together and can be lifted in pieces; liquids, which adhere but cannot, generally speaking, be lifted but in vessels; and airs, aeriform fluids or gases, which partake of this mobility in common with the atmosphere. The word gas has been generally introduced as expressing any particularly aeriform fluid, and the word air, chiefly restricted to the compound, the atmosphere. Gas has nearly the same meaning as spirit, being the German word gheest, which is used in that sense. The same substance may exist naturally in either of these three states: thus water may be solid as ice, liquid as water, and aeriform as vapour combined with the atmosphere; and in all changes from a mere solid structure to one less solid, a certain degree of heat is consumed, or rather enters into combination with the other substance; while in all changes, the other way, a certain quantity of heat is separated and becomes visible, in flame if the change be very rapid, and increasing the heat of other things if it be slow, this alteration of heat by these changes is important in many operations, both of nature and art, and in none more so than in the functions performed by the atmosphere. The next general property of the atmosphere is its weight, that is, its being like other substances subject to the law of gravitation. In consequence of this it can fill any cavity by entering at the bottom as well t the top. A very simple experiment proves the existence of this property: if a common drinking glass be put into a basin of water, sufficiently deep |