How much do you know of the great aërial ocean on the bottom of which you live and in which human beings are just beginning to fly? Its variations of heat, cold, sunshine, cloud, and tempest materially affect not only the health and happiness of man but his commercial and industrial welfare, and yet few know more than little of the wonders of the life-giving medium that so intimately concerns them.
At the Height of Two Hundred Miles. Here is only the invisible, the intangible ether which, while too tenuous to be detected or measured by any appliances of man, is supposed to transmit the rays of the sun. These rays, coming in the form of many different wave lengths, and with widely differing velocities of vibration, produce a multitude of phenomena as they are absorbed by or pass through the air, or as they reach the surface of the earth. The longer and slower waves are converted into heat, the shorter and more rapid ones into light, and the minutest movements probably into electricity.
Oxygen and nitrogen, which form the greater part of the atmospheric gases, absorb comparatively little of the solar rays, while water vapor, which constitutes a little more than one per cent. of the atmosphere and which remains close to the earth, absorbs large quantities. From the fact that one half of the atmosphere, including nearly all of its water vapor, lies below an elevation of three and one half miles, it becomes evident that the greater part of the absorption of the sun’s rays must take place in the lower strata. On clear days the atmosphere absorbs nearly one half of the sun’s heat rays; the remainder reaches the surface of the earth, warms it and in turn is radiated back into the air,—with this difference: that as earth radiation the wave motion of the rays is longer and slower than it was when the rays entered our atmosphere as solar radiation. In this slower form the rays are the more readily absorbed. The atmosphere is thus warmed largely from the bottom upwards, which accounts for the perpetual freezing temperatures of high mountain peaks, although they are nearer the sun than are the bases from which they rise.
At the Height of One Hundred Miles. The temperature at this altitude must be that of outside space, probably 459° F.[1] below zero. Air liquefies at 312° below, and therefore it cannot exist in the gaseous state in a region having a lower temperature. When it liquefies it has the color and general appearance of water, and about the same specific gravity.
When a piece of steel and a lighted taper are brought together inside of a vessel filled with liquid air, the dense supply of oxygen makes combustion so rapid that the hard metal burns like tinder.
At the Height of Fifty Miles. There is enough air here to refract light slightly, as at twilight, and to render luminous the meteors that rush with fearful velocity against its widely scattered molecules. At this distance from the earth there probably is no more air than would be found under the receiver of the best air pump, and, the reader will be surprised to learn, darkness is practically complete, although the hour may be midday, for there are no dust motes to scatter and diffuse and render visible the light rays of the sun. (See Chapter III.)
The Darkness of Outer Space. It may be proven by taking an inclosed volume of air, freeing it of dust motes, of which there are millions per cubic centimeter, and then trying to illuminate it; it will be found that no matter how powerful the light directed into it, it remains wholly dark. When one looks upward on a clear day, he apparently sees the whole universe illuminated; but in point of fact only the thin stratum of the earth’s air in which he lives is illuminated. Outer space is practically without temperature or light. The rays of the sun do not become either light or heat or electricity until they encounter the molecules of the air, or the invisible dust motes, or the cloud particles near the earth and through interference are transmuted from etheric vibrations into other forms of energy.
The Bacteria of Disease and of Putrefaction. These rapidly diminish in number with elevation, and on the tops of the highest mountain peaks practically none are found. Mid-ocean also shows but few.
At the Height of Twenty-five Miles. Air, light as it is, has still sufficient density to obstruct the passage of the minutest wave lengths of light, and here probably begins to be appreciable the blue tint of the heavenly vault. At this short distance from the earth there must be a deathlike stillness, for there is no medium sufficiently dense to transmit sound. Two persons could not hear each other speak, even if they could live in this rare atmosphere, which they could not. Here is eternal peace and no apparent motion, for storms and ascending and descending currents cease long before this level is reached. The cold is intense and daylight but a feeble illumination. There are no clouds.
Isothermal Stratum Entered at the Height of Seven Miles. We know that the temperature decreases rapidly with ascent—about one degree for each three hundred feet—until the top of the storm level is reached, at about seven miles, when a most wonderful discovery is made: the thermometer no longer falls as the aviator rises, or as balloons float to great altitudes carrying self-registering instruments. The temperature remains practically stationary, so far as exploration has been made, which is to the height of over nineteen miles. Major R. W. Schroeder, U. S. A., flew in an aëroplane to 36,000 feet and recorded a temperature of 69° below zero.
We have named this region above storms the Isothermal stratum. (See Figure 1.) Its temperature everywhere is about 70° below zero and it changes only about six degrees between winter and summer. Of course we must assume that ultimately the temperature shades away to practically nothing as outer space is reached.
Scientific and inventive genius is becoming so skillful in harnessing the forces of nature to man’s desires that it is reasonable to anticipate that within a quarter of a century or less human beings will be nearly as numerous in the air as insects, they will remain aloft longer, and sail to vastly greater distances and to higher altitudes. In time dirigible ships may sail for days and possibly for weeks in the pure air aloft, carrying millions of passengers.
At a Height of One and One Half Miles. There is little difference in the temperatures of day and night, except that the coolest time of the twenty-four hours is during daytime and not at night, as would be most naturally supposed. This is important information to an aviator or to the pilot of a balloon.
At an Altitude of One Thousand Feet. In free air at the hottest time in midsummer’s heat, the air is found to be as much as fifteen degrees lower than that at the ground. Almost within arm’s length of the streets of great inland cities there is a cool and healthful atmosphere when humanity is sweltering and dying from heat below. Some youth who is reading this may develop the genius that will lift up whole city blocks into this cool and healthful region. Open steel work below, the first level at one or two thousand feet above the hot streets, express elevators to carry passengers, and the climate of the cool mountain air is accessible to those who now live in discomfort at low populous centers. Man is just beginning to disport himself in the hitherto trackless wilderness of the air. Certain it is that the hanging gardens of Babylon will be outdone in the Twentieth Century and the eyrie of the eagle left far below by those who will live a part of their time in elevated structures having bases resting upon the earth; or who will fly to great distances aloft and remain at whatever altitude furnishes them the most pleasant and beneficial conditions, and that they may thus remain not only for days but for weeks without returning to the surface of the earth.
Only during recent years have we realized how thin is the stratum of air next to the earth which has sufficient heat and moisture for the inception, growth, and maturity of animal and vegetable life. The raising of the instrument shelter at the New York station of the U. S. Weather Bureau from an elevation of one hundred and fifty feet above the street to an altitude of three hundred feet has caused an apparent lowering of the mean annual temperature of two and one half degrees.
Air is so elastic and its density diminishes so rapidly with elevation that nearly one half of the weight of the entire mass of the atmosphere lies below the level of the top of Pike’s Peak, which has a height of a little less than three miles above sea level. It presses with a weight of about fifteen pounds per square inch of surface, and its pressure is exerted in all directions, upward as well as downward. An ordinary man sustains a pressure of over one ton on each square foot of his surface, but as the air penetrates all portions of his body and exercises a pressure outward as well as inward he feels no inconvenience. If his body could be so tightly sealed that no air could enter and if then the air of the interior should be removed with a pump, his body instantly would be crushed to a shapeless pulp.
A cubic foot of atmospheric air weighs one and one third ounces. Water is 773 times, and mercury ten thousand times, as dense as air. But air is a more ponderable substance than many suppose; an ordinary lecture hall forty by fifty feet and thirty feet from floor to ceiling contains two and one half tons of air at freezing temperature. It would contain less at a higher temperature, because heat expands its volume; it would contain more at a lower temperature, because cold contracts its volume.
Everything Evolved from the Air. Air is so common that we seldom stop to consider the magnitude of the force it exerts or the grandeur wrought by this invisible architect of nature. In the great cycle of world building—birth from the nebulæ, growth, maturity, decay, disintegration, death, and then possibly back again to the nebulæ—the atmosphere, be it light and tenuous as at present, or be it filled with the hot vapors of earth and metal, is the vehicle and the medium of the builder, transporting and transmuting, in mysterious ways and to wondrous forms, the materials of planets. Its work as a builder may be further illustrated by showing that the body of man itself returns not to the earth earthy, as we have been taught, but largely to the air whence it came. Decomposition is but the liberation of the aëriform gases of which it is mainly composed; the residue is but a handful that goes back to mother earth. Let us take the dried corn plant; weigh it, then burn it in a closed vessel so that none of the ashes can blow away. Continue the burning until the ashes are perfectly white and it will be found that the weight of the ashes is only about one twentieth of the weight of the great stalk, ear, and foliage we began with. What has become of all the rest? The fire has destroyed it, you say. No, we can destroy nothing. Remember that; we can destroy nothing that the Creator has made, neither matter nor force. The fire has simply changed the form of the plant; the nineteen twentieths that have disappeared have gone back to the air whence they came.
Thus we see that the body of man, the cereal and fruit that furnish him food, the structure that gives him shelter, aye, the many things that please the eye: the landscape, the beautiful flowers, the green fields, the babbling brooks, even the rose blush on the maiden’s cheek,[2]—really come from this wonderful fluid surrounding the earth, and well may it be said that the queen of life rides upon the crest of the wind.