VOL. III. No. 58.] SHARPE'S London Magazine: A JOURNAL OF ENTERTAINMENT AND INSTRUCTION A SCOTTISH SCENE.-(See Illustration.) "As they neared the land, the hills appeared to recede from them, and a little valley, formed by the descent of a small river from the mountains, evolved itself, as it were, upon their approach. The style of the country on each side was simply pastoral, and resembled in appearance and character the description of a forgotten Scottish poet, which runs nearly thus: "The water gently down a level slid With little din, but couthy what it made; The bonny banks all in a swarm did go.'"-SIR WALTER SCOTT. THE ATMOSPHERE. IN how many shapes does atmospheric influence present itself! In the brightness of a summer's morning we feel refreshed and delighted by the invigorating buoyancy of the air, and listen to the pleasant sound of the merry breeze, as it stirs the forest leaves, or ripples the surface of the lake. The countless forms of life around us,-feathered and insect tribes making the air their home, animals upon and in the earth, and the uncounted tenants of ocean,-all depend for existence on the agency of the atmosphere. The vegetable kingdoms, also, own their dependence on this mighty agent, which, covering all regions of the earth, is felt in every land, and by all orders of being. Let us then consider some of the most interesting circumstances connected with the atmosphere. It is principally composed of two gases, oxygen and nitrogen; but, as two other elements, carbonic acid gas and vapour, enter into its composition, we shall consider it to consist of these four substances. The chief gas is nitrogen, as, in 100 parts of the atmosphere, nearly eighty consist of this element, which is sometimes called azote, a term indicating its life-destroying properties. Four-fifths of that air, without which we must all perish, is therefore a most pernicious element, Thus vital and deadly gases are so beautifully mingled as to produce that life-sustaining fluid which every where girdles the earth, and invests it with countless forms of loveliness. Carbonic acid gas is also destructive to life; but this and the nitrogen are so adjusted to and worked up with the oxygen, that we gladly breathe the pure compound, and require it more constantly than any other nourishing agent. Before proceeding further, we must give the proportions in which these four substances exist in atmospheric air. If we take 100 cubic inches of air, and analyze the mass, we shall find it to consist of the following proportions: Thus it will be seen, that both by weight and bulk, the principal elements of the atmosphere are nitrogen and oxygen gas, the vapour and carbonic acid gas forming only about one and seven-fifths of a cubic inch in 100 inches. It will be seen that the gases destructive to life are far more abundant than the vital gas; but the commingling of all produces a wholesome fluid. As we stated in the article on Water, oxygen gas is without taste, colour, or smell, and so is the atmosphere. Nitrogen possesses the same properties, though differing in other respects. Carbonic acid gas is found in mines, where it causes the choke-damp; vast quantities are also locked up in limestone, a cubic yard of which has been calculated to contain 16,000 cubic feet of this gas, which some suppose to have formerly existed in immense quantities in the ancient atmosphere of the earth. Were the air wholly composed of oxygen, animal life would be hastened in all its movements, and, probably, speedily exhausted; whilst an atmosphere of nitrogen, or carbonic acid, though favourable to some forms of vegetable and animal life, would have rendered the earth unfit for man and terrestrial beings. But The mingling of the different gases in the atmosphere is a matter calling for our attention and admiration. Were each permitted to arrange itself according to weight, we should have an atmosphere composed of three distinct strata, the lowest being carbonic acid gas, the next oxygen, and the third nitrogen gas. This is the arrangement we should have expected the fluids to take by the natural laws of gravity. In such a disposition, the earth would have been a silent expanse; vast forests might have covered its surface; but no sound of life would have arisen from vale or mountain. this tendency to accumulate in strata, according to the weights, has been checked by another law, by which these various gases are so mingled together, that the carbonic acid, which would naturally have fallen to the surface of the earth, is diffused through the whole atmospheric mass, and does not compose more than theth part of the air. This tendency to diffusion is of vast importwith 500 men working there for eight hours; in that ance in our towns and dwellings. Take a factory, time 6,000,000 inches of carbonic acid is given off by respiration; were that product to accumulate, day after day, in our streets, depopulated cities would soon bear witness to its destructive qualities. The tendency of the gases to mingle prevents -a pours are forty-five miles above the surface of the globe; we naturally infer the existence of a supporting fluid, where those vapours float, and therefore conclude that our atmosphere extends to such an elevation. Some give to the air an altitude of fifty miles; but nothing like exactitude can be expected in calculations respecting a fluid, the density of which is exceedingly rare at great heights. Meteors have been observed sixty or a hundred miles above the earth; but it does not follow that such bodies must always take fire in the atmosphere, they may be exterior to it; no conclusion can therefore be formed respecting its extent from these phenomena. When, however, we represent the atmosphere as having an elevation of forty or fifty miles, it is not intended to assert that it maintains the same properties throughout the whole range; this is far from being the case. The density, for instance, must diminish with every mile of elevation, until at last a state of the greatest rarefaction is produced. Thus, at very slight heights, the air is too thin to admit of free respiration, and the discharge of a gun is scarcely heard, from the slight resistance offered to the exploded gas. If we ascend to the summits of the Andes or the Alps, and discharge a gun on the top of Chimborazo or Mont Blanc, the report is scarcely equal to that of a child's pop-gun,-so small is the resistance of the air at such heights. At an elevation of three and a half miles, the density of the air is one-half that upon the surface, a fact which can easily be tested, as aëronauts have attained to such heights; at fourteen miles it is reckoned at onesixteenth. these results. The gaseous proportions given above | lines through space, and that the reflecting vaare nearly the same in every part of the globe,fact illustrated by the experiments of the most eminent scientific chemists, who have analyzed the atmosphere in different climates, with the same general result. Some, however, have supposed that oxygen is more permanently abundant in some places; an opinion which has not been confirmed by experiment. But it may be said, that, if the atmosphere is every where composed of the same proportion of its gases, it ought to be equally healthy in all places, and the air of Sierra Leone as bracing as that of Devonshire. It must be remembered, however, that many circumstances combine to prevent, in some regions, the natural diffusion of the gases, or retard their mixture, from which it follows that some disturbances must happen in the animal economy. Thus, in a hot and thickly-wooded country, the free circulation of the air currents will be prevented, the atmospheric tide will not, so to speak, ebb and flow with due regularity, and a deleterious gas, such as carbonic acid, will take a longer time to diffuse itself, and is in the mean time breathed by animals. But, in all such cases, the natural tendency is to mingle in the proportions given above; such, therefore, may be considered the proper elements of the atmosphere. Every one knows that the quantity of vapour entering into the air must vary at different times, being much greater in hot than in cold weather, the difference being as to; but there is, nevertheless, an average quantity of such vapour mingled with the atmospheric gases, which is the proportion expressed in the tables. A similar remark applies to carbonic acid gas, the amount of which in the air is not always the same, being greater in dry seasons, but the moistened soil and saturated vegetation of a wet summer imbibe it largely from the air. 20 Was the atmosphere always supposed to be a compound fluid? No; men had breathed it for thousands of years without suspecting its compound character. Nor was it likely the viewless air should be deemed a complex fluid, when water, a more tangible and evident substance, was so long deemed simple. Until the year 1774, men were ignorant of the constituents of the atmosphere; but Priestley then obtained a glimpse of the truth in perceiving that oxygen entered into its composition; whilst Scheele, Lavoisier, Berthollet, Cavendish, and a host of enthusiastic students of Nature, soon gave to the world a true interpretation of many beautiful laws relating to the atmosphere. Into the history of these discoveries we cannot enter, nor wander into the rich and wide regions which on every side present their pure beauty to the eye, but confine our observations to the facts presented to our view in the atmosphere itself. The height of this world-belt cannot, of course, be ascertained by actual and close observation,the loftiest summits of the Andes do but pierce through the first stratum of air; nor has any aeronaut ever penetrated to its remoter depths. We are, nevertheless, able to make a tolerable guess at the depth of this gaseous sea which surrounds us, and forty-five miles is usually regarded as the height to which our atmosphere extends. One means by which we arrive at this calculation is, the reflection of light. The process may thus be described: suppose we observe a certain portion of light from the sun arrested by vapours, and reflected to the earth, instead of passing in straight Were the density preserved the same through the whole height of the atmosphere, the pressure would far exceed that which now weighs down with a force of fifteen pounds every square inch of the globe. This would occasion a corresponding change in our bodies, the temperature of our climates, the growth of vegetables, and in the whole organized world. We should be bowea down by an ever-crushing weight; no flower would raise its delicate head above the ground, whilst every gale must become a furious and destructive tempest. On the other hand, were the atmosphere at the same density from top to bottom as at the height of seven miles, we should not be able to exist; the blood must become corrupted; no refreshing breezes ever felt; and, in all probability, a perpetual winter would rule over the earth. All these consequences are prevented by the present adjustment of the atmosphere, by which the parts nearest the earth are of the density requisite for the support of animal and vegetable life, and the portions above so gradually attenuated as to keep the whole atmospherical machine in perfect order. This attenuation of the air has no assignable limits, but continues to increase the higher we go. It has been calculated that a cubic inch of our air, taken from any part of the earth's surface, would become so expanded at the height of five hundred miles, as to fill a space equal to the whole bulk of the planet Saturn. Thus the atmosphere may be described as a series of numerous air-strata, diminishing in density as they ascend. It is, perhaps, needless to remark, that the higher we rise the less is the pressure of the atmosphere upon us, as may be proved by the gradual fall of the barometer while ascending a mountain. Let us suppose ourselves at the foot of some lofty hill; we observe the barometer, and perhaps find the column of mercury standing at thirty inches high; we begin the ascent, and, having gained an elevation of some hundred yards, again observe the instrument; the quicksilver has fallen. We again proceed; the fluid still continues to fall the higher we rise. This results from the diminishing pressure of each more elevated stratum of air upon the mercury in the bowl of the barometer; the metal therefore falls in the tube and rises in the bowl. If we descend, the increasing aerial pressure forces the fluid from the receptacle into the tube again. The uses of this atmospherical pressure are various: it prevents the water of seas and rivers from being too rapidly evaporated by heat, which would cause an undue saturation of the air, and the production of a perpetual rain. It also enables us to heat water to a much higher degree than we otherwise could, as it now preserves the fluid form until heated to 212° of Fahrenheit's thermometer. Were the pressure of the atmosphere much less, water could not be raised to such a temperature, but must be turned into steam before fitted for many of its present purposes, in the preparation of food, and manufacturing operations. The common pump depends upon this atmospherical pressure. When a child sees water issuing from the spout of a pump, he imagines that the water is raised by the action of the handle, drawing up the contents of the well: and such may be the notion of many very old men too. In fact the water is not drawn up at all: the air is pumped out of the pipe, and the water rushes in to take the place of this fluid. Why does the water rush up the empty pipe? It is forced upwards by the pressure of the air in the well on its surface, and rises to the height of about thirty-four feet, above which the common pump will not raise water. Thus the construction of this domestic machine depends upon the universal and unchanging laws which rule the atmosphere. This effect of aerial pressure was long ascribed to a peculiar property supposed to belong to all matter, and which was called nature's dread of a vacuum. When, it was said, air is withdrawn from the pump-tube, the surrounding water rushes in to fill the vacancy, because nature abhors emptiness. We should say, because it is forced up by the pressure of the superincumbent atmosphere; and we are right. Let us not, however, fall into the silly habit of ridiculing the men of olden times for their ignorance in these matters; they gave the best explanations in their power of the phenomena around them, and we can do no more; but our opportunities for observing Nature working in her secret places, and dealing with her strange mysteries, are superior to theirs; let us rejoice for ourselves, but forbear from insulting those who gazed from a valley at the objects which we calmly survey from high mountain summits. The atmosphere may be reduced by means of the air-pump to any degree of rarefaction, even to three hundred times less than its usual density. This is not surprising, since if a cubic foot of air be in a vessel, and the air pump applied, 299 parts may be pumped out; when the 1-300th part will still attempt to fill the vessel. However small the quantity left in the receiver, it will attempt to occupy the whole space, but its effects are then so trifling as to be inappreciable. Air is not only capable of such extreme rarefaction, that no instruments can detect its presence, but will take a liquid form. To accomplish this result it must be subjected to vast artificial pressure, amounting to 30,000 lbs. on every square inch. This state of condensation is, however, wholly artificial, and never exhibited in any natural operation, the greatest pressure being that which we feel on the surface of the earth. Liquefaction of the atmosphere cannot therefore be a natural result. The peculiar conformation of the atmosphere has a strong influence upon the laws of vision, and the phenomena of light. When we walk abroad in the early beauty of a summer's morning, we see a thousand objects from the hill top, which we have climbed for the sake of the prospect, and a softly-diffused light invites the eye to scan plains, hills, forests, rivers, and the distant sea, with its playfully agitated waters. The atmosphere is fitted to receive light; there is, therefore, a peculiar relation, a species of brotherhood, between the air and light, by which they act in concert, one adapting itself to the other. Suppose the atmosphere were so constituted as to resist light, to prevent its reflection, or refraction, or to separate it into its different colours, how altered would be the aspect of all things! A bright overpowering glare, a dazzling kaleidoscopical earth, with a sharp and painful light, would be our lot, instead of the beauties which now gladden the eye and exalt the taste. What a powerful agent is the atmosphere in the production of sounds! without it the globe might abound with living myriads; but silence, the sign of death, would be the law of all existence in earth and air. Those numberless sounds from the world of rejoicing insects, the fine and touching harmonies of birds, the solemn echoes of woodland voices, and the deep tones of the water-fall, would be unknown. What a singular change in our mode of life, the matter of our thoughts, and the nature of language, does this suggest! Thus we see how closely our present mode of being is linked to certain particular arrangements of two or three invisible gases, and how fluid matter is made the medium of intercourse with our fellowcreatures, and with the most impressive forms of natural beauty. How various are the results thus produced from one agent! life supported, vegetation upheld, rivers and seas kept in their channels, light and sound made vehicles of delight and interest; all by the duly-adjusted workings of a fluid which attracts not the notice of one-tenth of those living in the very sight of its wondrous agency, and beneath the most direct manifestations of its sublime power. This atmosphere is not a quiescent mass of stratified air, but active as the ocean, and perpetually excited by numberless currents blowing in every direction, and at all elevations. Every peasant, though bookless and unlearned-every school-boy, though regarding the rule of three as the limit of science, has a knowledge of those movements, which, in breeze, storm, or hurricane, roll their aerial waves through the lower regions of the air. But vast tidal streams-the Mississippis of the atmosphere-are perpetually flowing in the higher regions; some sweeping from the equator towards the poles, others heaving their invisible billows towards earth's central line. Besides these movements, there are multitudes of minor ebbings | and flowings, by which the salubrity of the globe is preserved, and numerous meteorological phenomena produced. When we gaze into the clear blue deeps of the sky, all seems still in that expanse; a thousand wonderful movements are, nevertheless, continually operating in these seemingly passive regions. Common observers may often notice these diverse agencies, and especially the different currents of air setting in opposite directions. Frequently, when we feel a breeze blowing towards one point of the compass, the clouds are seen to move in the opposite direction, intimating the existence of a contrary current at that elevation; whilst, higher still, other atmospheric rivers are distinguished, bearing along their light cloudy films. That all such movements are necessary to the accurate working of the great machine-that each is under the control of well-devised and harmoniously-acting laws, we cannot doubt, though such agencies are yet hidden from the scrutiny of our philosophy. When these hidden mysteries of the atmosphere become known in their full significance, we shall see the wisdom and love of the Deity as beautifully developed in the movements of the air as in the courses of the stars. is drawn into the lungs: it must undergo a pecu- When the exhausted blood returns to the lungs for fresh food, it has a deep purplish hue, but, having received the oxygen, it rushes off on its errand, exhibiting a brilliant scarlet tint. How does the oxygen reach the blood? Through the thin membranes of the vessels, which are, in some cases, not more than a thousandth part of an inch in thickness. These delicate tubes are spread, like a system of the finest net-work, about the aircells of the lungs, and by such exquisite agencies the great business of life is carried on. The nitrogen of the air is not used by the lungs, and is therefore returned, by respiration, to the atmosphere around us; thus, with a nice discrimination, the vital gas is separated from the noxious; the former being instantly absorbed, the latter rejected. Carbonic acid gas, a fluid most destructive to animal life, is formed by breathing. For the oxygen which has been separated from the atmosphere, and united with the blood, does not return to the air, but carbonic acid gas is formed by its combustion, which is given out in large quantities by respiration, and vitiates the air around. When it is considered that 40,000 cubic inches of this deleterious gas are respired by one man every day, it will be seen how pernicious a long confinement in close rooms and crowded factories must be to the becomes noxious by the carbonic acid poured into it, and, unless a good system of ventilation exist, the lungs will be gradually poisoned, the blood deprived of its vital energies, strange diseases commence their attack on the constitution, and consumption slowly urge its victim to the grave. A man may exist in health on the simplest food, and on surprisingly small quantities; but diminish his proper supply of oxygen, and death begins to work. Let us now consider the atmosphere as supplying to the human frame those gases which feed the ever-active flame of life within us, by furnishing, from the first to the last moment of our earthly existence, a constant supply of air to the lungs. The vital energies in each human body may be likened to a furnace, which requires an incessant supply of fuel; part of this fuel is supplied by the oxygen extracted from the air by the beautiful agency of the lungs. This singular machine consists of two soft divisions, called the right and left lobes, and is composed of countless air-cells and blood-human constitution. In such places the air soon vessels, the latter of which penetrate every part of the former, in order to expose the blood within them to the action of the air. Were the blood injected into the lungs in one mass, much of it must remain beyond the influence of the air; the surface alone would experience its agency. To secure the exposure of every portion of the blood to the aerial influence, it was necessary that it should be subdivided into minute tubes, around which the freshly-inhaled atmosphere may readily press. Few are aware of the vast extent of lung-surface thus exposed to the air in consequence of its division into these passages and channels, an area which some reckon at 150 square feet. To cool such a surface requires an immense quantity of air, and the lungs are accordingly fitted to hold above 300 cubic inches, which are drawn in through the nostrils incessantly. What quantity of air is required daily for one man? Let us suppose that twenty inspirations are made every minute; that forty cubic inches are received into the lungs by each of these efforts; this will give 800 cubic inches of the atmosphere to support breathing for one minute only. Thus a man requires each day of his life 1,152,000 cubic inches of wholesome air. From this constant inrush of a cold fluid to the lungs it happens that they are the coolest part of the body. But how is this vast quantity used up? through what process does it pass? This air is but the raw material, so to speak, which is to be worked up by an elaborate system of machinery. The air is useless to the vital system in the shape in which it exists around us, and in which it All classes of the animal kingdom depend for existence upon the atmospherical influences; some requiring more air than man, as birds, others less, as reptiles. Fish procure oxygen from the water by the gills, which are complicated machines adapted for this purpose. Some have imagined that certain reptiles are able to exist without a supply of air; and strange stories are recorded of toads, shut up for ages in the solid rock. But many of these reports rest upon suspicious authorities, and are weakened by certain experiments recently made to test this presumed vital capacity of the toad. In the year 1825, Dr. Buckland enclosed twelve toads in holes, cut in hard sandstone, but all died within a year. Dr. Macartney also found that a week's separation from air sufficed to destroy life in a toad. Thus it seems unlikely that these animals can exist for long periods without air, in the manner described by some marvel-mongers. Our conclusion is, that the atmosphere contains an element essential to the support of life, and wherever living creatures are found, deep in the ocean-waters, or beneath the earth's surface, there |