THE OCEAN OF AIR

Taranaki Daily News, 10 February 1934, Page 13 (Supplement)

THE OCEAN OF AIR

QUEER WORLD AT BOTTOM

(By

the Rev. B. Dudley, F.R.A.S.)

When we speak of the materials constituting the atmospheric ocean, at the bottom of which we dwell, being as “light as air,” we grossly violate the truth. Not even the most well informed person realises, except by an effort of the mind, the great density of the air he breathes. Suddenly remove the air pressure from within above the pressure of the miles . weighs would crush you instantly, f oo t more than a ton to the The experienced airman mter ? statement that we live in an not in the metaphorical u i . sense, for he knows-smce he feeta the atmosphere under his spread it is substantial. Ages ago it was state that if you hit the air hard enough, it is a solid; and the air pilot tods it to be so. It is so solid, indeed,, that he actually climbs or rests upon it. At the bottom of this sea is a of gases. Near the surface of the earth about 78 per cent, of the a^ volume is oxygen, about 21 P e . nitrogen and 0.94 argon. The remamnio substances are mixed with the J^ d ™eh smaller quantities. Those named not components of two or more elementa they are chemical elements. Nitrogen and argon are said to be chermca. y - ert because they do not readi y form chemical compounds with other elements. ■Oxygen differs from them inasmuch a it ta a very active element, and easily unites with others. It has been out that if there had been 0^ mal one per cent, or even one-tenth per cent, more free hydrogen on the sm face of the earth, apparently the free oxygen which is now in the air would have united with it, in the formation .of water, and left the atmosphere tirely without this element on which all higher forms of life depend. A balloon released at the bottom of this sea'of gas decreases its buoyancy with every mile it rises, . density of the air decreases with the altitude. At a height of three miles the density is only half as great as at the surface of the earth, at 12 miles only one-tenth as great, and at 24 miles; <my one-four hundredth. Sixty miles : above the earth’s surface the air is 12,000 times rarer than the atmosphere we breathe. In composition, too, at that height, i very different, 90 per cent, being hydrogen. The greatest heights reached by artillery projectiles are about 25 miles.

We are evidently hot-house creatures who could quite easily freeze to death. Only a short distance overhead the mn cent looking cirrus clouds which give so many pretty effects to the eye are made up of ice-spicules, afloat m arctic cold. Above us, but a little, is deadly cold; even as below our feet, under the surface of the earth, is equally deadly heat. So that we . belong to a tiny margin between the two and dare not, if we could, venture .outside it.

There are several methods by which the depth of this ocean of air has been determined. A careful observation of meteors or shooting stars enables us attain ’an approximation. These bodies are minute masses utterly invisible until they “hit the air hard enough” to become luminous from the friction set up. The height at which the atmosphere is dense enough to render a meteor incandescent can be ascertained by noting from- two widely separated places on the earth the directions at which it first becomes visible. Such observations show that meteors first become visible, as a rule, at a height of from 60 to 90 miles. From this it can safely be inferred that the air is about 100 miles high. We never see meteors, as such, when they are nearer to the earths surface than 30 to 45 miles.

Another means of getting at the height of the atmosphere is found in the auroral lights, a phenomenon belonging to the upper air, at altitudes where- it is extremely thin. An aurora is an electrical effect, probably caused by ionized particles which pour out constantly from the sun and are sometimes drawn in upon the earth. The altitude _of an auroral streamer is measurable in precisely the same way as that used in computing the height at which a meteor becomes visible. And it has been proved that the phenomenon occurs hi portions of the atmosphere which are much too rare to have sensible- effects upon the velocities of meteors.

A third test is the duration of twilights. Ere the sun rises the dawn has long heralded its coming, as in the evening the lengthened • twilight keeps alive its memory. Both dawn and twilight are due to upper portions of the atmosphere being illuminated while the sun itself is below the observer’s horizon. At the heights of meteors and auroral displays the atmosphere does not reflect sufficient sunlight to be .visible. It is impossible, of course, to decide exactly when twilight ceases, but it has been found that under favourable conditions of weather the day’s afterglow does not entirely fade away until the sun is about 18 degrees below the horizon. The conclusion arrived at is that traces of solar light can be seen at least 50 miles above the earth’s surface.

It used to be thought that in all probability the decrease in temperature with altitude occurred gradually. And up to about 6 or 7 miles of ascent this is actually the case. The fall is at the rate of 18 degrees Fahrenheit for each mile regularly. Beyond that height, however, as is ascertained when balloon-soundings are made, no further decrease takes place. Throughout a wide stratum of air the temperature is almost constant at about 70 degrees below zero. Only in the regions below this do storms occur. There are reasons for the conclusion that at the upper limits of the atmosphere temperature is comparable with the absolute cold of stellar space, viz., 459 degrees below zero.

Enveloped within this wrapping of gas the human race struts about on the surface of a ball, which is itself in other than a gaseous condition only because the temperature has, in the evolution of things, become too low to maintain it in that state. At the bottom of this ocean we congratulate ourselves on our fine achievements; we love and hate by turns; we clamour for place and power; we exult with joy or moan with pain and sorrow. Every living thing nevertheless is a centre from which the world is apprehended; and, as Amiel reminded us, even if we are as fish in the depths of an ocean, at whatever point of the planet we are stationed we are equally near to heaven and the infinite.