Aria

“ LXXVIII. who has there proved by experiments with the air-gun and air-pump, that when any portion of the atmosphere becomes mechanically expanded, it absorbs heat from the bodies in its vicinity. And as the air which creeps along the plains, expands itself by a part of the pressure being taken off when it ascends the sides of mountains; it at the same time attracts heat from the summits of those mountains, or other bodies which happen to be immersed in it, and thus produces cold. ”

“ For here the wind not only has free scope, but it also finds another element, fluid but incompressible, to obey its impulse and follow in the course which it takes. If the WIND be like a wild spirit, the WATER is a mighty, irresistible body, endowed with motion by the other, and capable of any work, from the drowning of a sea-gull to the wrecking of a stately ship. ”

“ The varieties of cloud-form and the mixture of structures are of course infinite, but still the delicate fibrous or hairy clouds, the lovely white fleeces on the blue sky, the mountainous rocky masses, and the curious drooping festoons of cloud, are all only the products of condensation under different circumstances.
The result of all modern research leads to the general conception that we live below a sea of air mixed with watery vapour; and that the earth has a coating of that physical manifestation which is called electricity. ”

“ Now, besides the mutual Affinity that Water has to almost all Kinds of Air, and to Floguiston; added to its Power of Absorption; and as the sea, particularly in Summer, also rivers and damp meadows are generally cooler than the Lands and Countries bordering on them; Currents of damp cool Air press forwards to supply the Defect or Vacancy caused by Heat, Rarefaction and Elevation of dry warm Air, which is necessarily, and almost constantly rising into the Atmosphere, from heated Lands, Plains, and gentle Eminences long shone on by the Sun. ”

“ This air, driving the vapour everywhere as it rushes along, produces gales and constantly increasing currents by its mighty blasts. Wherever the winds carry the vapour which rolls in masses from springs, rivers, marshes, and the sea, it is brought together by the heat of the sun, drawn off, and carried upward in the form of clouds; then these clouds are supported by the current of air until they come to mountains, where they are broken up from the shock of the collision and the gales, turn into water on account of their own fulness and weight, and in that form are dispersed upon the earth. ”

“ In that community when the wind is south, the people fall ill; when it is northwest, it sets them coughing; with a north wind they do indeed recover but cannot stand about in the alleys and streets, owing to the severe cold.
2. Wind is a flowing wave of air, moving hither and thither in­definitely. It is produced when heat meets moisture, the rush of heat generating a mighty current of air. That this is the fact we may learn from bronze eolipiles, and thus by means of a scientific invention discover a divine truth lurking in the laws of the heav­ens. ”

“ It is not clear whether the light of the cloud means the lightning again or the varied hues which make an Oriental sunset glorious in purple and gold. But the balancings of the clouds must be that singular power which the atmosphere has of sustaining vast quantities of watery vapour—either miles above the earth's surface where the filmy cirrhus floats, dazzling white against the blue sky, or lower down where the rain-cloud trails along the hill-tops. ”

“ After sunset, when the sky is clear, you know that the grass gets wet with dew. In the morning you may see mists hanging over woods, and streams, and hills, and gradually melting away as the sun mounts in the sky. At all times of the year you may watch how clouds form and dissolve, and form again, ever changing their size and shape as they move through the air. Now these are all examples of the condensation of vapor. ”

“ It is something to have learned so much at all events with regard to the composition of the air we breathe. But we have been able to find out a great deal more, and to discover that the behaviour of these little molecules is of the most extraordinary and vivacious description. That air is eminently mobile is sufficiently obvious; but the air which fans our faces, or the wind which turns our windmills, or even the hurricane which devastates whole towns, gives only a very imperfect idea of the real mobility of air. ”

“ Mountains may be more cloudy and rainy than plains, for the currents of air that cross them must rise, and in rising they cool by expansion and often reach the dew point of the air, moisture being precipitated in the form of clouds, rain, or snow. ”

“ Let the clouds appear as driven by tempestuous winds against the summits of lofty mountains, enveloping those mountains, and breaking and recoiling with redoubled force, like waves against a rocky shore. The air should be rendered awfully dark, by the mist, dust, and thick clouds. ”

“ Everything is saturated and dripping with moisture; the very air we breathed seemed a clammy, aromatic vapor. In these vast forests atmospheric changes are continuous and abrupt; drifting banks of gloomy clouds are followed by glaring sunshine, and then tempestuous showers—all in rapid succession. ”

“ When we were talking about the clouds we learnt that from every wet place, as well as from the seas, lakes, and rivers, water is constantly being drawn up, so that we can see it again in the fleecy clouds which float across the sky, and again when it comes down in the showers which water the earth—the tiny heat-waves are the messengers which perform this work of evaporation. ”

“ Wind then by agitating the air should contribute to cool the earth and warm the atmosphere, by bringing a more rapid succession of fresh strata of air in contact with the earth, and yet in general wind feels cooler than still air? ”

“ The second region or stratum of air terminates I suppose where the twilight ceases to be refracted, that is, where the air is 3000 times rarer than at the surface of the earth; and where it seems probable that the common air ends, and is surrounded by an atmosphere of inflammable gas tenfold rarer than itself. ”

“ Offices of the cloud-ring.—Returning and taking up the train of contemplation as to the office which this belt of clouds, as it encircles the earth, performs in the system of oceanic adaptations, we may see how the cloud-ring and calm zone which it overshadows perform the office both of ventricle and auricle in the immense atmospherical heart, where the heat and the forces which give vitality and power to the system are brought into play—where dynamical strength is gathered, and an impulse given to the air sufficient to send it thence through its long and tortuous channels of circulation. ”

“ So, as the cooler air from above drops down, it acts like a mirror to the breath of the earth or the air that lies close over it; and this air is condensed into mist. All through the night both air and earth are cooling, but the earth more slowly, so that there is still a meeting of cooler and warmer air and consequent condensations, and the mist is hovering over the meadows when the next morning’s sun rises. As the sun mounts up, it begins to spread its warmth and the upper air is the first to feel it. Growing warm, it rises, drawing up after it the cooler air below. ”

“ Both land and water are heated by the sun’s rays, and the same change in the air then takes place which we find also at our firesides. The layer of air next the warmed earth becomes itself warmed. As it thereby grows lighter it ascends, and its place is taken by colder air, which flows in from the neighborhood to take its place. This flowing in of air is wind.
One of the most important ingredients in the air is the vapor of water. ”

“ To know whether the Air is hazy, tho’ the Sun continues shining.
The Method taken for that Purpose was by placing the Hand so as to cover his Disk or Body, and then observe the Glory blazing round him; which may, in general, be seen to issue in great Abundance, in Rays of a golden Colour: occasioned by a Haziness or Vapour which pervades the lower Regions of the Air, most frequently in the hottest and calmest Weather, and in the hottest Climates. ”

“ Look up at the clouds as you go home, and think that the water of which they are made has all been drawn up invisibly through the air. Not, however, necessarily here in London, for we have already seen that air travels as wind all over the world, rushing in to fill spaces made by rising air wherever they occur, and so these clouds may be made of vapour collected in the Mediterranean, or in the Gulf of Mexico off the coast of America, or even, if the wind is from the north, of chilly particles gathered from the surface of Greenland ice and snow, and brought here by the moving currents of air. ”

“ I know nothing to which the wind has not some happy use. Is there a grain of dust so small the wind shall not find it out? Ground in the mill-wheel of the centuries, the iron of the distant mountain floats like gossamer, and is drunk up as dew by leaf and living lung. A thousand miles of cloud go by from morn till night, passing overhead without a sound; the immense packs, a mile square, succeed to each other, side by side, laid parallel, book-shape, coming up from the horizon and widening as they approach. ”

“ It is seen when the wind is in the act of changing its direction, and the clouds, arrested in their march, are thrown out of rank. That which was the side becomes the rear of the cloud, and is banked up by the sudden pressure. Clouds coming in from the sea are met with a land wind, and so diverted. ”

“ Perched on such an uncertain support, they walk with the mincing steps and swaying gait which, for them, constitute the acme of grace, but which, in barbarian eyes, suggest nothing more alluring than an imminent danger of toppling over. ”

“ Forests produce rain. Under the influence of vertical sun-rays trees exhale the aqueous vapors which their leaves have absorbed from the atmosphere, and in contact with the night-air or any stray current of lower temperature, these vapors discharge rain-showers even in midsummer, and at a great distance from the sea. ”

“ It is little more than a drift of the air in all its quills, it breathes through its whole frame and flesh and glows with air in its flying, like blown flames; it rests upon the air, subdues it, surpasses it, outraces it,—is the air, conscious of itself, conquering itself, ruling itself. ”

“ Place me on the coasts beyond the tropics—place me where the wind blows toward the shore in the day-time, and toward the sea by night—and I instantly advance toward conclusive experiments. For example, I know that the heat of the sun during the day rarefies the air over the land, and so causes the wind. ”

“ We have learned further, that the vapor of which clouds are formed is resolved into rain and snow, and, in one or other of these forms, descends to the earth again. There is thus a circulation of water between the solid earth beneath and the air above. This circulation is as essential to the earth in making it a fit habitation for living things, as the circulation of blood is in keeping our bodies alive. ”

“ After nightfall the air on mountain peaks and on hills and ridges soon becomes cooler than the air at the same elevation out over the open valley, due to contact with the elevated earth, which radiates heat and cools faster than the air. ”

“ Clouds, you doubtless know, are masses of vapor from water. Now, when these vapors are sufficiently condensed to acquire a certain weight, they can no longer float in the atmosphere, and they fall in the form of rain. But they fall in rain because they have to traverse the air in order to fall to the ground. ”

“ There was not the least breath of wind to bring cooler air to the heated soil upon which we lay. Our lungs struggled to gulp down as much air as possible, and we could not bear to turn our eyes upon the glowing atmosphere. ”

“ You now produced for yourself in miniature a storm and wind. The air that has been heated rises over a heated area, and cooler air from all directions around is passing into the space underneath the chimney and taking the place of the heated air that has gone up. This experiment illustrates what takes place, except on a smaller scale, out in the atmosphere when a portion of the earth becomes heated. ”

“ Thus over a level plain on a clear calm night there is found a relatively thin layer of cold air near the ground, which increases in temperature up to two hundred or three hundred feet, or which may be only five or ten feet deep. ”

“ If fixed air tend to correct air which has been injured by animal respiration or putrefaction, lime kilns, which discharge great quantities of fixed air, may be wholesome in the neighbourhood of populous cities, the atmosphere of which must abound with putrid effluvia. ”

“ Cloud is formed by the cooling by expansion [288] as currents of air are carried aloft. Clouds are composed of minute watery droplets or of ice spiculæ, depending on their temperature, and the latter largely is determined by elevation. A cloud differs from mist or rain in the size and number of its particles, and from fog in its position and the method of its formation. ”

“ The moist air fares like the wet clothes we spoke of; the warm dry air absorbs its particles of water. But if a colder stratum of air approaches the stratum containing clouds, then the water-particles of the latter are condensed; the cloud becomes small drops of water; these drops are too heavy to be supported in the air, and they fall down as rain. ”

“ The invisible rays, as we have said, dissolve the ice into rivers.
The atmosphere produces clouds by expansion of vapour, which chills or cools it, and it descends as rain. To prove that expansion cools air is easy by experiment, but if we have no apparatus we must make use of our mouths. In the body the breath is warm, as we can assure ourselves by opening our mouths wide and breathing upon our hands. ”