Air current

“ When a current of air is created naturally or artificially in the open air or in a room, you perceive at once an increased velocity in their motion; they move with rapidity in all directions; but when a strong current or wind prevails, they are carried with it in a stream, preserving however, as yet, their irregular up and down motion.
10. Its formation is sometimes very rapid, and its accumulation very thick in the lower strata of our atmosphere, but the intensity is variable. ”

“ But we have pointed out that if the rate of cooling as we ascend in the still air is less than the rate at which an ascending current will be dynamically cooled, such a rising current will come to rest. If, on the other hand, the rate of cooling in the ascending current be less than in the still air, the equilibrium will be unstable, and a violent uprush will result. ”

“ That heavier and lighter air may move in currents of different and even opposite direction, appears sometimes by the clouds that happen to be in those currents, as plainly as by the smoke in the experiment above-mentioned. Also in opening a door between two chambers, one of which has been warmed, by holding a candle near the top, near the bottom, and near the middle, you will find a strong current of warm air passing out of the warmed room above, and another of cool air entering below; while in the middle there is little or no motion. ”

“ A. Yes; animals reject the nitrogen of the air (as not suited to the use of animal life) , but vegetables absorb it, as it is the food they live on; and thus the vegetable world restores the equilibrium of the air, disturbed by man and other animals.
Q. Is air a good conductor?
A. No; air is a very bad conductor.
Q. How is air heated?
A. By “convective currents.”
Q. What are meant by “convective currents?”
A. When a portion of air is heated, it rises upward in a current, carrying the heat with it: other colder air succeeds, and (being heated in a similar way) [Pg 246] ascends also ”

“ A. The current of hot air up the chimney, striking against the oblique vanes of the smoke-jack, drives them round and round; in the same way as the sails of a wind-mill are driven round by the wind.
Q. Why are some things solid, others liquid, and others gaseous?
A. As heat enters any substance, it drives its particles further asunder; and a solid (like ice) becomes a liquid; and a liquid (like water) becomes a gas.
Q. Why does water simmer before it boils?
A. The particles of water near the bottom of the kettle (being formed into steam sooner than the rest) shoot upwards ”

“ But as regards the process by which the electricity of the atmosphere is developed, we have, up to the present time, no certain knowledge. It has been said that electricity may be generated in the atmosphere by the friction of the air itself, and of the minute particles floating in it, against the surface of the earth, against trees and buildings, against rocks, cliffs, and mountains. ”

“ Just as water, by seeking its own level, acquires an even and uniform pressure, so the electricity of the air seeks an even and uniform potential. If a body of cold, dry and highly charged air flows into a region of low potential, or into one oppositely charged, an interchange, or flow of electricity, results. ”

“ The mechanical arrangement by which the light is produced consists of a series of concentric rings, perforated on the upper surface for the escape of the gas, placed at equal distances from each other, and so arranged as to regulate the quantity of atmospheric air, and to communicate by conduction and radiation sufficient heat to raise the temperature of the gas to a given point, so as to effect the separation of its charcoal immediately on its leaving the burner, and then, by an arrangement above, to bring fresh atmospheric air to the proper points of the flame. ”

“ The flame, therefore, is negative, and it tends by its presence to reduce the positive charge of electricity which generally characterizes the air of fine weather to zero, or to change it to a feebly negative-charge. We learn from various writers upon meteorology that the normal electricity of the atmosphere is positive. ”

“ See note VII. Atmospheric air is a bad conductor of electricity and thence confines it on the body where it is accumulated, but when it is made very rare, as in the exhausted receiver, the electric aura passes away immediately to any distance. The same circumstance probably happens in respect to heat, which is thus kept by the denser air on the plains from escaping, but is dissipated on the hills where the air is thinner. 4. As the currents of air rise up the sides of mountains they become mechanically rarefied, the pressure of the incumbent column lessening as they ascend. ”

“ 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. ”

“ Q. What is meant by “convection of hot and cold currents?”
A. The air (which is heated by the surface of the earth) ascends, warming the air through which it passes. Other air (being warmed in a similar way) also ascends, carrying heat; till all the air is made hot.
[Pg 220]
Q. Is the air made cold in a similar way?
A. Yes. The air resting on the earth is made cold by contact: this cold air makes the air above it cold; and cold currents or winds shake the whole together, till all becomes of one temperature. ”

“ Provided, therefore, with these modern and more refined means of observation, we are in a condition to study the fluctuations of that subtile manifestation of energy which is ever present in the air, and seems to lurk in all matter. The influence of the electrical state of the air upon atmospheric changes is doubtless far-reaching. We are accustomed to think of thunder-storms as the only manifestations of atmospheric electricity ”

“ 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. Eolipiles are hollow bronze balls, with a very small opening through which water is poured into them. Set before a fire, not a breath issues from them before they get warm; but as soon as they begin to boil, out comes a strong blast due to the fire. ”

“ Every substance must possess surface and the molecules of the gases composing the air are not an exception; neither are the dust particles floating in the air; therefore they act as condensers, receiving and discharging electrons. ”

“ In clear weather we find the air near to the earth in a neutral condition, but gradually assuming the condition of a positive charge as we ascend; so that the upper air and the earth are oppositely charged like the two sides of a Leyden jar or two leaves of a condenser. This condition is intensified and localized when a thunder-cloud passes over the earth. The moisture globules have been charged with potential energy by the power of the sun's rays when evaporation took place ”

“ But varying external influences, such as currents of air, caused by opening doors, or by persons passing along near the apparatus during the progress of an experiment, which would introduce disturbing irregularities, can best be guarded against by such spaces as I have described, filled with the poorest heat-conductor and the lightest solid substance attainable. Air, although a poor heat-conductor, and extremely light, is diathermous, and offers no obstruction to the escape of radiant heat. ”

“ A schoolboy’s knowledge of the change of temperature always accompanying the compression of air would prevent such an assertion from being made by anyone who had witnessed the operation of the Liberator in the production and storage of etheric force, during which there is not the slightest change of temperature. ”

“ These ceaseless motions, it must be clear, contribute greatly to the cooling of our bodies; but the effect is most marked in the open air, when we are exposed to the action of the winds. In our climate, the average velocity of the atmospheric currents is about ten feet a second, or seven miles an hour. Supposing that the extent of the surface of the body exposed to the currents is one square metre, there pass over a man walking out for an hour about eleven thousand cubic metres of fresh air. ”

“ As currents of air, with the clouds therein, pass different ways, 'tis easy to conceive how the clouds, passing over each other, may attract each other, and so come near enough for the electrical stroke. ”

“ When the air, with its vapours raised from the ocean between the tropics, comes to descend in the polar regions, and to be in contact with the vapours arising there, the electrical fire they brought begins to be communicated, and is seen in clear nights, being first visible where 'tis first in motion, that is, where the contact begins, or in the most northern part ”

“ Now these hot gases rising up thus on all sides would leave room below for cooler gases to pour down from above, and these, as we know, would cut off, or absorb, much of the light coming from the body of the sun, so that the centre, where the down current was the strongest, would appear black even though some light would pass through. ”

“ Fundamental Facts regarding Atmospheric Electricity.—The general electrical condition of the atmosphere is positive in relation to the surface of the earth and ocean, becoming more and more positive as the altitude increases. When the sky is overcast, and the clouds are moving in different directions, it is subject to great and sudden variations, changing rapidly from positive to negative, and the reverse. ”

“ The observations of atmospheric electricity consist essentially in determining the amount and character of the difference of potential between two points not very far distant from each other, as, for instance, the end of the pipe from which the water-drops are discharged, and the nearest point of the earth or buildings resting on the earth. ”

“ In the production of aërial currents, heat is converted into force, and hence vapor is converted into watery globules mechanically suspended on clouds, which, by their friction, sweep the electrical ether into excessive condensation in the great Leyden-jar arrangement of the sky. ”

“ In all probability the action of the sun’s rays upon the earth’s surface, producing a constantly varying difference of temperature, and also the temperature which has been observed as existing at great depths, give rise to thermo-electrical currents, which may play an important part in the results thus briefly described. ”

“ Is not the Heat of the warm Room convey'd through the Vacuum by the Vibrations of a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum? And is not this Medium the same with that Medium by which Light is refracted and reflected, and by whose Vibrations Light communicates Heat to Bodies, and is put into Fits of easy Reflexion and easy Transmission? And do not the Vibrations of this Medium in hot Bodies contribute to the intenseness and duration of their Heat? ”

“ 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. ”

“ It will be seen that my apparatus for experiments on air is, in fact, nothing more than the apparatus of Dr. Hales, Dr. Brownrigg, and Mr. Cavendish, diversified, and made a little more simple. ”

“ In the pause, after the Susquehanna's disaster Bert became aware of a trivial sound like the noise of an ill-greased, ill-hung door that falls ajar—the sound of the men in the Furst Bismarck cheering.
And in that pause in the uproar too, the sun rose, the dark waters became luminously blue, and a torrent of golden light irradiated the world. It came like a sudden smile in a scene of hate and terror. The cloud veil had vanished as if by magic, and the whole immensity of the German air-fleet was revealed in the sky; the air-fleet stooping now upon its prey. ”

“ Friendship is evanescent in every man's experience, and remembered like heat lightning in past summers. Fair and flitting like a summer cloud;—there is always some vapor in the air, no matter how long the drought; there are even April showers. Surely from time to time, for its vestiges never depart, it floats through our atmosphere. ”

“ In the morning the sun rose brilliant and quickly wore away the thin layer of ice that covered the water, and all the warm air was quivering with the steam that rose up from the quickened earth. ”

“ It requires but little imagination to see in the flying earth a living monster followed by shadowy furies which hurl themselves upon it, now vainly attempting to reach the air-protected body or again striking it with terrific force, lodging deep in its sides amid loud reverberation and dazzling blaze of light. ”

“ Through the constant revolution of the fifth element, with all contained therein, the four elements are forced to move and to change their respective positions, so that fire and air are driven into the water, and again these three elements enter the depth of the earth. Thus are the elements mixed together; and when they return to their respective places, parts of the earth, in quitting their places, move together with the water, the air and the fire. In this whole process the elements act and react upon each other. ”