A SYNOPTIC PICTURE OF THE AIR
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.
[Illustration: FIG. 1.—Winter and Summer Vertical Temperature
Gradients, in degrees Centigrade and Fahrenheit.]
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.