THE AIR ABOVE US
Monograph Number Five in The Mentor Reading Course
ETEOROLOGISTS are not content to limit their investigations to the stratum of air lying close to the earth's surface. Even before the demands of the aeronaut for information concerning the structure and phenomena of the atmosphere far overhead became pressing, many efforts had been made to secure such information, in view of its important bearing upon many scientific problems. As long ago as the year 1784 a balloonist, equipped with various meteorological instruments, made an ascent from London and brought back an interesting series of observations, which were communicated to the Royal Society. For more than a century the manned balloon was the principal means of sounding the upper atmosphere.
Nowadays, as a rule, the meteorologist, instead of going aloft in person, sends up a kite or a balloon to which are attached automatically registering instruments. When the aerial vehicle returns to earth its record shows in detail the conditions encountered during the journey.
Everybody remembers how Franklin brought lightning from the clouds; but it is a far cry from the simple apparatus that served Franklin's purpose to the "box kite" of modern meteorology. Science has perfected the kite almost beyond recognition. It has been shorn of that crucial feature of the schoolboy article, the tail. Even the kite "string" has become several miles of steel piano wire, wound around the drum of a power-driven winch, with elaborate apparatus for recording the force of the pull, and the angles of azimuth and altitude.
Captive balloons are sometimes used for similar investigations. When, however, it is desired to attain great altitudes the meteorologist has recourse to the so-called "sounding-balloon," which is not tethered to the earth. This is usually made of india-rubber, and when launched is inflated to less than its full capacity. As it rises to regions of diminished air pressure it gradually expands, and finally bursts at an elevation approximately determined in advance. A linen cap, serving as a parachute, or sometimes an auxiliary balloon which does not burst, serves to waft the apparatus, with its delicate self-registering instruments, gently to the ground. This commonly happens many miles—sometimes two hundred or more—from the place of ascent. Attached to the apparatus is a ticket offering the finder a reward for its return, and giving instructions as to packing and shipping. Sooner or later it usually comes back; though often months after it falls. Indeed, the large percentage of records recovered, even in sparsely settled countries, is not the least remarkable feature of this novel method of research. The instruments attached to sounding-balloons register the temperature of the air, the barometric pressure, and sometimes the humidity.
By means of the sounding-balloon the air is explored to heights of twenty miles and more! The records obtained by means of these balloons have, within the past fifteen years, completely revolutionized our ideas concerning the upper atmosphere.
Still another device employed by meteorologists is the pilot-balloon. This is also a free balloon, but carries no meteorological instruments. Its motion in the air is followed by means of a theodolite, and it serves to show the speed and direction of the wind at different levels. During the winter of 1912-13 a pilot-balloon sent up from Godhavn, Greenland, by a Danish exploring expedition reached the unprecedented altitude of more than 24 miles.
PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION
ILLUSTRATION FOR THE MENTOR, VOL. 4, No. 10, SERIAL No. 110
COPYRIGHT, 1916, BY THE MENTOR ASSOCIATION, INC.
THE EFFECTS OF SNOW AND ICE—THE CAMPUS, PRINCETON UNIVERSITY
