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the weather, it will be necessary to consider, briefly, some of the properties and constituent parts of that wondrous envelope of our globe.* Concise VIEW OF THE PROPERTIES AND CONSTITUTION OF THE
ATMOSPHERE. That the atmosphere is a fluid completely surrounding the whole earth needs no demonstration; how far its dimensions extend into space is a problem of far more difficult solution. Had it been a fluid of uniform den. sity, the length of the mercurial column suspended in the barometer, would have demonstrated that its greatest elevation could not have exceeded five miles; but the air being very elastic, the higher portions of the mass which covers our globe, sustaining a diminished pressure, must swell upwards, and occupy a proportionably wider space. This property removes the boundary of the atmosphere to a much higher elevation; and from the consideration that the reflection of the Sun's rays, unless the sky be overcast, is constant, so that there is total darkness in no climate, even at midnight, it has been inferred, that the elevation of the atmosphere must, at least, be equal to 1638 miles. This very great extension of a rare expansive atmosphere appears conformable to the general phenomena. Near the equator it may stretch out even much further, and yet its elevation can never exceed a certain absolute limit. Though this extreme boundary may surpass all our ordinary conceptions, it yet scarcely exceeds the twentieth part of the distance of the Moon, which was held by the ancients to communicate with our atmosphere.
Though we can sound the depths of this great aërial ocean but approximately, we are not so situated with regard to its weight. This property has been long demonstrated to exist, and even those differences of pressure upon the earth, its supporting surface, which must attend the fluctuations of a body of such attenuated fluidity perpetually agitated, can be measured and compared.
To the properties of magnitude and weight must be added those of elas. ticity, expansibility, transparency, and insipidity.
Air is also generally considered to be invisible, but it is certain that, like water, it is a colored fluid; it is naturally blue, as that of the latter is green,
* It would be extremely difficult, in an article which involves so great a number of facts and opinions, to assign an individual authority to each of the following statements. It is, therefore, proper to mention, that the authors who have been principally consulted for this abridgment of a very extensive and complicated subject, are these :
Daniell, J. F., Esq., F. R. 8.—“Meteorological Essays and Observations." 2d edit.
Leslie, Professor.–Articles“ Climate” and “ Meteorology," in the Supplement to the Encyclopædia Britannica; and “ On Heat and Moisture."
Forster, Thos., Esq.--Article “Cloud,” in Sapplement to Ency. Brit.
but both colors acquire intensity only from the depth of the transparent mass. This we perceive in air, on viewing distant objects, whose colors are always tinted by the deepening hues of the interjacent range of atmos. phere. The remotest hills seem lost in a cerulean vesture. The blending of the atmospheric azure with the colors of the solar rays, produces those compound, and sometimes remarkable, tints with which the sky and clouds are emblazoned.
The constitution of the rare medium in which we “ live, and move, and have our being,” has been unfolded by the brilliant discoveries of modern chemistry. Experiments have been made at distant points, repeated on the suminits of the loftiest mountains, and applied to portions of air brought down by balloons from the altitude of five miles; and the result has been the conclusion, that the constitution of our atmosphere is the same in all places on the surface of the earth, and at every elevation that has yet been explored. It appears to consist of a combination of two distinct expansible gases, the interstices of which are penetrated by ever-varying proportions of condensible elastic vapor. The gases are combined in different quantities, a single portion of oxygen being united to three parts by weight, or four parts by bulk, of nitrogen; there is also a very slight admixture of carbonic acid gas, amounting to perhaps a thousandth part of the whole. The particles of the condensible elastic vapor or steam are invisible, and insinuate themselves between the particles of air, and filter through them with as little union, but with a similar kind of retardation, as those of water ascend and diffuse themselves through a sponge. These distinct atmospheres of air and vapor thus mechanically mixed, have different relations to heat, and their states of equilibrium, when enveloping a sphere of unequal temperature, are incompatible with each other.
The triple assemblage is constantly exposed to the action of heat, a principle scarcely known but by some of its properties, which, combining with all bodies, even the most dense, either enlarges their bulk, or, dissolving the tie which holds their atoms in a solid form, sets them loose in fluidity, or finally expands them into vapor, and removes the seat of their existence from the earth to the heavens. The quantity of heat absolutely present in any one place is extremely difficult to measure; but its fluctuations are perpetual, and often evident. And as every accession or diminution of temperature is accompanied by some change, and often more than one, in the integral parts of bodies, or in the relation of one body to others which may be contiguous, it follows that these changes are infinite in number and character, and that the agent which produces them may be considered the main-spring of all the grand movements in the atmosphere.
The atmosphere, so compounded, may be considered a universal solvent, and though itself inodorous, it is the medium of all smells, and dissolving the different odorous effluvia, is charged with the emanations of all the various substances it sweeps.
There is still to be added to this enumeration of the ingredients of this astonishing compound, the subtle and mysterious agencies of light, and of the electric, galvanic, and magnetic fluids; and last, as if to baffle all inquiry, and render analysis impossible, there is, in universal operation, a perpetual agitation and commixion of the whole mass.
When we reflect upon this ever-agitated heterogeneous fluid, compounded of the most active elements of life and destruction, constantly combining, -separating, now evident to the most ordinary sense, now escaping the grasp of imagination, we cannot, rationally, be surprised at the little, comparatively, that is really known concerning it. All within the power of the most ardent student is to collect the few facts that are established, to dismiss conjecture and hypothesis, and to apply himself to make additions to our knowledge by carefully observing, and accurately and luminously describing, the processes during which he is permitted to be present.
“ By invisible, but ever-active agencies, the waters of the deep are raised into the air, whence their distribution follows, as it were by measure and weight, in proportion to the beneficial effects which they are calculated to produce. By gradual, but almost insensible expansions, the equipoised currents of the atmosphere are disturbed, the stormy winds arise, and the waves of the sea are lifted up; and that stagnation of air and water is prevented, which would be fatal to animal existence. But the force which operates is calculated and proportioned; the very agent which causes the disturbance, bears with it its own check, and the storm, as it vents its force, is itself setting the bounds of its own fury.'
It is evident, from a slight view of these “complicated and beautiful contrivances,” that it is hopeless to expect that all the causes of the phenomena of the atmosphere will ever be entirely attained by human science. At present but few are known, and those imperfectly. Ainongst the principal ones which most affect the subject of our present inquiry are, undoubtedly, heat and electricity. The first raises and suspends the evaporated waters invisibly in the air, until some more powerful attraction dissolves the union, and the deserted moisture, exposed to view, falls again to the earth, and revisits it in the varied forms of clouds, mist, rain, dew, snow, hail, sleet, and hoar-frost. To electricity may be principally attributed the more splendid phenomena of lightning, the aurora-borealis, and the other igneous meteors. And the effect of these causes, variously combined and infinitely modified by other agents, is felt in those currents of atmospheric air, which are described by a sacred writer, as “ going toward the north, and toward the south, as whirling about continually and returning again according to their circuits.”
Imperfect as the preceding sketch necessarily is, it is founded on facts which have been collected by some of the most indefatigable observers,
and faithful historians, of what they saw. While it enables us to judge a little more correctly, perhaps, of some of the causes of those conditions of our atmosphere, which are hourly presenting themselves to our view, or affecting the state of our existence, it cannot but excite emotions of astonishment and of pity, when we see some of the most ignorant of our species boldly pretending to predict the results of the operations, visible and invisible, near and remote, of this vast and complex, and almost unknown apparatus.
We shall present a contrast to the dicta of these daring empirics, by an extract from the recent publication of a gentleman, * highly distinguished by the services he has rendered meteorology, which contains a few of the most general and best authenticated facts relating to the phenomena of the atmosphere. From these we may safely reason; and a knowledge of them may frequently enable us to detect order and regularity among objects proverbially spoken of as uncertain and irregular.
SOME OF THE MORE PARTICULAR PHENOMENA OF THE
ATMOSPHERE OF THE EARTH. . « The mean height of the barometer (i. e. the mean weight or pressure of the atmosphere) at the level of the sea, is the same in every part of the globe.
“ The barometer constantly descends in a geometrical progression for equal ascents in the atmosphere, subject to a correction for the decreasing temperature of the elevation.
“ The mean temperature of the earth's surface increases gradually from the poles to the equator.
“ The mean temperature of the atmosphere decreases from below upwards in a regular gradation.
“ The barometer at the level of the sea is but slightly affected by the annual or diurnal fluctuations of temperature; but, in the higher regions of the atınosphere, is, on the contrary, greatly affected by them.
“ The heating and cooling of the atmosphere, by the changes of day and night, take place equally throughout its mass.
“ The average quantity of vapor in the atmosphere decreases from below upwards, and from the equator to the poles.
“ The western coasts of the extra-tropical climates have a much higher mean temperature than the eastern coasts.
“A wind generally sets from the sea to the land during the day, and from the land to the sea during the night, especially in hot climates.
“ Between the tropics the fluctuations of the barometer do not much exceed one quarter of an inch, while beyond this space they reach to three inches.
* Daniell. Essays.
“ In the temperate climates the rains and the winds are variable.
“ As we advance towards the Polar Regions, we find the irregularities of the wind increased; and storins and calms repeatedly alternate, without warning or progression.
“ In the extra-tropical climates, a fall in the barometer almost always precedes a period of rain, and indicates a change or acceleration of the aërial currents.
“ Barometers, situated at great distances from each other, often rise and fall together with great regularity.
“More than two currents may often be traced in the atmosphere at one time, by the motions of clouds, &c.
“ The force of the winds does not always decrease as the elevation increases ; but, on the contrary, is often found to augment rapidly.
“ The variations of the barometer are less in high situations than in those at the level of the sea.
In Great Britain, upon an average of ten years, westerly winds exceed the easterly in the proportion of 225 to-140; and the northerly winds exceed the southerly, as 192 to 173.
“ Northerly winds almost invariably raise the barometer, while southerly winds as constantly depress it.
“ The most permanent rains from this climate come from the southern regions.
“ The mean height of the barometer varies but little with the changes of the seasons.
“ The apparent permanency and stationary aspect of a cloud is often an optical deception, arising from the solution of moisture on one side, and its precipitation on the other.
“ The quantity of vapor in the atmosphere in the different seasons of the year (ineasured on the surface of the earth, and near the level of the sea) follows the progress of the mean temperature.
“ The pressure of the aqueous atmosphere, separated from that of the aërial, generally exhibits directly opposite changes to the latter.
“ Great falls of the baroineter are generally accompanied by a tempera. ture above the mean for the season, and great rises by one below the
The same authority also states, that “ The British islands are situated in such a manner as to be subject to all the circumstances which can possibly be supposed to render a climate irregular and variable. Placed nearly in the centre of the temperate zone, where the range of temperature is very great, their atmosphere is subject, on the one side, to the impressions of the largest continent of the world; and, on the other, to those of the vast Atlantic Ocean. Upon their coasts the great stream of aqueous vapor, perpetually arising from the western waters, first receives the influence of the land, whence emanate those condensations and expansions which de