Rarefied air

“ A case more frequently to be met with is where currents of air set down Chimnies in consequence of a diminution and rarefaction of the air in a room, occasioned by the doors of the room opening into passages or courts where the air is rarefied by the action of some particular winds. ”

“ Remous are probably caused by electrical disturbances of the atmosphere, which cause the air streams to meet and mingle, breaking up into filaments or banding rills of air. The wind—that is, air in motion—far from being of approximate uniformity, is, under most ordinary conditions, irregular almost beyond conception, and it is with such great irregularities in the force of the air streams that airmen have constantly to contend. ”

“ In going from convectionally still air into an updraught, he gets a “bump.” The same result is apparent if, while traversing a downdraught, he strikes still air.
It has been noted that the air ranges itself in layers differing in density, temperature, and moisture content. In many cases an acquired sense born of experience enables the airman to discern these layers and to adjust the wings of his plane in encountering them. Frequently a sheet of smoke or dust separates two cloud layers and experience has taught how to avoid or how to penetrate it.
Air is either going up or coming down. ”

“ Alternate currents, especially of high frequencies, pass with astonishing freedom through even slightly rarefied gases. The upper strata of the air are rarefied. To reach a number of miles out into space requires the overcoming of difficulties of a merely mechanical nature. ”

“ When you stand on the ground and turn your eyes upward all the sky looks alike. But it's far from it. It's full of all kinds of winds, currents and strata, pockets, of which all aviators stand in deadly fear, mists, vapors, clouds of every degree of thickness and complexion, and then you have thunder and lightning, just as you do on land and sea. It's these shifting elements that make the navigation of the air so dangerous, John. The whole question would be solved, if there was nothing but stationary air, growing thinner in exact proportion as we rise. ”

“ The heavens at times are hung with a great veil of what is called "high fog." This bank of vapor shuts out all the upper sky. Between it and the earth is a stratum of hot, dry air, down through which the collected moisture above can never descend. It has to float off to the distant mountains. It has to be caught by their rocky arms, and turned into rain or snow, and then descend as rivers to the dry and dusty plains beneath.
When we were starting out on our carriage ride in the morning, as I noticed this lowering mass of vapor above us, I asked the driver if it was going to rain. ”

“ The surrounding Air is instantly contracted by Condensation, during the Absence of the Sun’s Rays, and therefore occupies a less Space: fresh Air is received, and as instantly dispersed by Expansion towards those Parts, which are the warmest, i. e. where there is least Resistance: so that a gentle216 Breeze is constantly kept up, probably by a Depression from above.⁠ [86]
281. Analagous to this, are those Winds which generally rise early and die away at Sunset: the nocturnal Condensation of the Air being sufficient for the reception: as Air suffers some Compression without Tumult. ”

“ 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. ”

“ But what the self-torturers are really afraid of is a "draught;" in other words, air in motion. Perceptible currents of air, no matter how pure, no matter how passionately welcomed by the miasma-clogged lungs, they dread as messengers of death. Their fear of night-air is founded chiefly on the circumstance that the cooling of the atmosphere generates air-currents within a few hours after the sunset even of the sultriest day. So they close their bedroom windows or nail them down; they invent double window-sashes and "weather-strips," to exclude the slightest breath of life-air. ”

“ Although the motion of the air depends on a great number of causes, there are nevertheless principal ones, of which it is difficult to estimate the effects, because of the modifications from secondary causes. The most powerful cause is the heat of the sun, which produces successively a considerable rarefaction in different parts of the atmosphere, and gives rise to an east wind that constantly blows between the tropics, where rarefaction is the greatest. ”

“ Standing on an open heath on a gusty day, we may often note the rhythmic buffeting of the wind, resembling the assault of rolling billows of air. The evidence of these billows has been actually traced far aloft in balloon travel, when aeronauts, looking down on a wind-swept surface of cloud, have observed this surface to be thrown into a series of rolls of vapour, which were but vast and veritable waves of air. ”

“ Later experiments proved, however, what every one now knows, that the paper-bag rose, not because of the gases given off by the fire, but by reason of the hot air with which it became filled. Nearly all substances, no matter how solid, expand more or less under the influence of heat, and air expands very greatly indeed. By thus expanding heated air becomes lighter than the surrounding air, and, because it is lighter, rises upwards in the atmosphere, and continues to rise until it has once more regained the average temperature.
Montgolfier’s Balloon. ”

“ I myself had formerly this prejudice, this aerophobia, as I now account it, and dreading the supposed dangerous effects of cool air, I considered it as an enemy, and closed with extreme care every crevice in the rooms I inhabited. Experience has convinced me of my error. I now look upon fresh air as a friend: I even sleep with an open window. I am persuaded that no common air from without, is so unwholesome as the air within a close room that has been often breathed and not changed. ”

“ That quantity of water which had been frozen by the mixture of snow and salt, was almost as much like snow as ice, such a quantity of air-bubbles were contained in it, by which it was prodigiously increased in bulk.
The pressure of the atmosphere assists very considerably in keeping fixed air confined in water; for in an exhausted receiver, Pyrmont water will absolutely boil, by the copious discharge of its air. ”

“ And does not the Effect of a sudden Calm, suppose the Wind to descend from above with a Kind of saltatory Motion, instantly counteracted by the new elastic Air?—For if the Wind be supposed to blow sideways or horizontally,210 to any considerable Height above the Water, woud not the fresh lateral Air glide away, and prevent the Continuance of the Calm?
269. When a Squall happens, or only Rain falls; Air will rush from all Sides, and from above, to supply the Vacancy of the fallen Cloud and Vapour.
The Air immediately above must fall: the lateral Air gravitating towards other Places. ”

“ If the apparatus is in a darkened room, and a powerful beam of light from a lantern is sent through the receiver, the damp air will be seen to be quite clear; but a stroke or two of the pump removes some of the air, the remainder is chilled by its own expansion, and a dense cloud is precipitated. ”

“ But it requires a much more violent and longer continued agitation of air in water than is ever occasioned by the waves of the sea to do the least sensible injury to it. Indeed a light agitation of air in putrid water injures it very materially; but if the water be sweet, this effect is not produced, except by a long and tedious operation, whereas it requires but a very short time, in comparison, to restore a quantity of any of the most noxious kinds of air to a very great degree of wholesomeness by the same process. ”

“ But an expanding body always becomes colder as the result of its expansion. Thus the vapour-laden air is chilled by its expansion. It is also chilled by coming in contact with the colder, higher air. The consequence is that the invisible vapour which it [Pg 267] contains is chilled, and forms into tiny water-drops, like the steam from a kettle or the funnel of the locomotive. And so, as the air rises and becomes colder, the vapour gathers into visible masses, which we call clouds. ”

“ While the air is thus calm below, the circling wisps of vapor high up on the mountain, rising and descending, show that the battle between the sun and the clouds is still raging. From above the saturated forests, the rising vapors condense and increase in size till at length, caught in some counter-current, they are swept away or carried downward, while the dissolving cloud spreads out in wisps and streamers till suddenly it disappears into transparent air,—a veritable cloud ghost. ”

“ Snow and ice and fibrous and porous substances are poor conductors, and are called insulators. Air and water are also poor conductors. The fur of animals and the feathers of birds protect against the rapid loss of heat because they contain numerous interstices filled with air, a poor conductor. Heat is lost by radiation when the molecules of matter set up vibration in the ether. The atmosphere itself performs this function on a large scale when the sky is cloudless, so that radiated heat is not absorbed by the cloud covering and its loss into space restricted. ”

“ No matter how fiercely the sun might shine, life on the earth would be entirely destroyed by cold.
When water vapor, clouds, or dust motes intercept certain portions of the sun’s rays, they change them from vibrations in ether to the motions of molecules, and the motions of these molecules are expressed in a rise in temperature in the vapor, cloud, or dust. Earth radiations of heat, having longer and slower wave lengths than those that come from the sun, are more readily absorbed by the atmosphere. ”

“ In the future the traveler in the upper reaches of the atmosphere will carry oxygen and make the kind of air that he wishes to breathe, and he will properly protect himself against the cold of his new world, which he will find deficient in dust motes and doubtless entirely wanting in the bacteria of putrefaction and of disease. ”

“ The pure vapor of water, for example, is a gas as invisible as the air itself. It is everywhere diffused through the air; but, unlike the oxygen and nitrogen of the atmosphere, it is not constant in quantity. We have now to examine whether meteorological observations do not clearly indicate its influence on terrestrial radiation:
January 16th.—Extremely serene; air almost a dead calm; shy without a cloud ”

“ On the other hand, if the air contain transparent vapour, and the sky appear clear, the counter-radiation will be less, the earth will cool rapidly, and the deposit of dew will be copious; provided the night be comparatively calm, for, when the wind blows, the circulating air supplies heat to the radiating substances, and prevents any considerable chilling. ”

“ Having once remarked the foregoing Process at Leisure; the same may be seen over any open Vessel of Water just warm enough to emit visible Steam: but the Air shoud be as still and calm as possible: the Steam never rising from all Parts of the Surface at once; but a depressing Spunge of Air always descends to the Surface, the Instant a Lamina of Vapour has been detached. ”

“ A mouse will live very well, though a candle will not burn in the residuum of the purest fixed air that I can make; and I once made a very large quantity for the sole purpose of this experiment. This, therefore, seems to be one instance of the generation of genuine common air, though vitiated in some degree. It is also another proof of the residuum of fixed air being, in part at least, common air, that it becomes turbid, and is diminished by the mixture of nitrous air, as will be explained hereafter. ”

“ He replied, “all bodies exposed in a clear night must undoubtedly radiate as much of their heat during a storm as in the most perfect calm; but, whenever radiation is going on, the air is more or less warmed by it; and consequently wind, which is only air in motion, serves to bring a continual stream of its warm particles into contact with those bodies. This restores almost as much heat as they had lost, and prevents the deposition of dew; for, you know, dew is nothing but the moisture of the atmosphere condensed by meeting with colder substances ”

“ The lightning itself, however, often does mischief. This happens when the discharge, instead of being between two clouds in the air, takes place between a cloud and the ground—a cloud surcharged with electricity understood. Then all intervening objects are struck by the fluid."
"There, however, you are wrong," said Fritz. "All objects are not struck; on the contrary, the fluid avoids some things and searches out others, even moving in a zig-zag direction to manifest these caprices; it often discharges itself on or into hard substances, and passes by those which are soft or feeble." ”

“ Down and down the crowd goes through the long winding, cold, damp, rancid-smelling passages, devoid of the remotest gleam of ventilation, and where one breathes air so thick and foul that it sticks to one's clothes and furs one's tongue, throat and lungs for several hours after one has emerged from the catacombs into fresh air again. ”