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THE NEW AIR WORLD

Fig. 4.—Instrument Shelter. Frontispiece.
([Page 66])

THE
NEW AIR WORLD

The Science of Meteorology
Simplified

BY

WILLIS LUTHER MOORE, Sc.D., LL.D.

PROFESSOR METEOROLOGY GEORGE WASHINGTON
UNIVERSITY, EIGHTEEN YEARS CHIEF
UNITED STATES WEATHER BUREAU

BOSTON

LITTLE, BROWN, AND COMPANY

1922

Copyright, 1922,

By Little, Brown, and Company.

All rights reserved

Published October, 1922

Printed in the United States of America

AFFECTIONATELY DEDICATED
TO
A FRIEND OF MANY AND PLEASANT YEARS
A BELOVED TEACHER AND A
GREAT CHEMIST

Dr. CHARLES E. MUNROE, Ph.D.

INTRODUCTION

The author’s “Descriptive Meteorology” (Appleton, 1914) is designed for the teaching of those who intend to make Meteorology a profession. This book is planned for the reading of those who desire to know something of the wonders of the New Air World into which man is just now entering, for those who desire to become weatherwise and make forecasts for themselves, and to apply their knowledge to their business, their health, and their happiness; and for the reading of the more advanced pupils of the public schools.

So far as possible technical terms are avoided and an effort made to tell a simple story that will awaken curiosity and lead the reader to wish to know more and more of the mysteries of the atmosphere, of which practically nothing was known at the time of the landing of the Pilgrims, Torricelli not having discovered the barometer until twenty-three years later. It will be made plain how atmospheric air was formed, how long it will remain, whither it will go, how it is heated, cooled, and lighted; where and how storms, cold waves, clouds, frosts, and fair-weather conditions originate and how move; how the cyclone, the tornado, and the thunderstorm may be recognized on the Daily Weather Map of the Government and their future activities forecast; how a fund of simple yet wonderful information that will be of inestimable value may be acquired by any intelligent person.

The author acknowledges courtesies extended to him by Prof. Charles F. Marvin, present chief of the Weather Bureau, and by R. H. Weightman, chief clerk of the Bureau, in the matter of securing several important illustrations; and like favors extended to him by D. Appleton and Company, John Wiley & Sons, and the Taylor Instrument Company, of Rochester, N. Y.

W. L. M.

August, 1922

CONTENTS

LIST OF FIGURES

LIST OF CHARTS

THE NEW AIR WORLD

CHAPTER I
ATMOSPHERES OF THE EARTH, THE SUN,
AND THE PLANETS

How Atmospheres Are Formed. Once there were no such things on the earth as hills and mountains, singing brooks, roaring rivers and vast oceans; and the delicately hued landscape, with its winding roads, hedges, flowers, green fields, and golden grain, had not evolved from the atmosphere. The earth had not yet cooled down to the condition of a solid crust, everything that the eye now sees existed in the form of invisible gases, or as clouds incandescent with white heat. Fiery blasts swirled over the face of the earth. Storms a million times more powerful than the most destructive West Indian hurricane of the present day moved through the indescribably hot atmosphere, throwing down not rain as we understand it, but liquid earth and metal, as their rising clouds ascended and cooled. It is difficult for the human mind to grasp the wonders of this.

Small planets cool quicker than large ones and sooner come to the conditions of a crust and to a temperature suitable for the development of the various forms of life.

Atmosphere of the Sun. To the unaided eye it appears as a smooth, bright, quiescent sphere, but the telescope reveals millions of agitations and hundreds of red flames that shoot outward to distances of hundreds of thousands of miles. One can form no adequate picture of the convulsions of the atmosphere of the sun. During eclipses, when the intense glare of its center is obscured, hydrogen flames may be seen darting outward for as much as a million miles.

Lifeless Planets. The larger a planet the longer is the time that must elapse before the hot vapors of rock and metal, which largely compose its early atmosphere, cool and congeal into a crust, leaving as a residual an atmosphere of such heat, density, and composition as to permit of the beginnings of the forms of life that have inhabited the world. Before the sun can reach this condition, an indescribable period will have elapsed, its light will have gone out, its heat will have ceased to reach the earth and the other planets in quantities sufficient to maintain life, the earth will have been dead millions of years, and the sun itself will only receive heat and light from the feeble rays of the stars that, unlike itself, have not yet ceased to shine. But even then the sun ever must remain dead, for there is no external source whence it may receive heat. No vegetation can adorn it, no water flow upon its surface, neither can the foot of any man press its soil.

Jupiter, and perhaps Neptune, Uranus, and Saturn, have hot atmospheres still in violent agitation,—molten surfaces composed of all kinds of matter, from which bubble and boil off hot clouds of vapor that surge about in huge eddies or cyclonic storms, and that here and there are shot outward in tongues of fire. The earth millions of years ago had a similar atmosphere. But when the heat energy of these vaporous planets wanes, and they cool down, as the earth did many years ago, the simplest forms of life cannot be evolved upon them, for they are too far away from the sun to receive life-giving heat. Mars receives less than half the intensity of the solar rays that come to the earth, Jupiter only 0.037, Saturn 0.011, Uranus 0.003, and Neptune 0.001.

In due time—some hundreds of millions of years—the cooling of the sun will leave the earth to freeze and all life to become extinct, unless, perchance, the oxygen of the air is so far absorbed by its rocks, or filtered away into space, as to destroy life before that time. No matter what may be the achievements of the human mind, what wonderful civilizations may be developed, what powerful empires created, or what wonderful secrets of creation discovered, it seems certain that these all will pass away, and finally the surface of the earth be as if man never lived. The dust of ages will wipe out and obliterate every trace and vestige of the operations of life. Silence, cold, and darkness will then reign supreme. But the time of this is indescribably far off in the future, and man will have ample opportunity to develop to the highest mental and spiritual estates of which he has inherent possibilities.

The moon already is dead. If it is formed of matter abandoned by the earth, as we believe, it once must have had an atmosphere, a portion of which was absorbed by its rocks as it cooled, and the remainder lost as the result of the low power of attraction of so small a body, which is insufficient to prevent the darting molecules of the gases of its air from shooting off into space. The absence of an atmospheric covering allows the heat from the sun to escape almost as rapidly as it is received; and the long nights of the moon (each as long as fourteen of our days) during which the sun’s rays are entirely cut off, permit the temperature of the dark side to fall to something like -400° F.

How Atmospheres Are Maintained and How Lost. The processes of nature are always adding to the various gases of the atmosphere in some ways, and transforming or taking from them in other ways. On the earth the loss and the gain are so nearly equal as to maintain at present a nearly constant condition. Marked changes have taken place, however, in long geologic periods. Our early atmosphere probably contained large quantities of carbon dioxide which were absorbed by the rank vegetable growth that now forms the coal beds of the earth, and the slowly cooling rocks that constitute the crust took in large quantities of oxygen; in fact, nearly one half of the weight of the crust of the earth is composed of the latter element.

In consequence it may be said that our present atmosphere is what remained after the earth had absorbed its gases nearly to depletion, and after the lighter gases, like hydrogen and helium, which seem to have too great molecular velocity to be imprisoned by the earth’s attraction of gravitation, had been lost in space. Gases that cannot be held by the moon may be imprisoned by the earth and those that can escape from the earth may be held by the larger planets.

Height of the Earth’s Atmosphere. Exact computation has shown that if the air were the same density at all elevations, which it is not, it would extend upward a distance of only five miles. From laws that are well understood it is known that at a height of thirty miles the atmosphere is only about one hundredth as dense as it is at the surface of the earth, and that at fifty miles it is too light to manifest a measurable pressure. The oxygen ceases at about thirty miles and the nitrogen at about fifty miles, the water vapor being restricted below the five-mile level. The appearance of meteors, which are rendered luminous by rushing into the earth’s atmosphere, and whose altitudes have been determined by simultaneous observations at several stations, reveals the presence of hydrogen and helium at a height of nearly two hundred miles.

CHAPTER II
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.

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.

CHAPTER III
EXPLORATION OF THE ATMOSPHERE

DISCOVERIES AS VALUABLE TO THE FUTURE AS THOSE MADE BY COLUMBUS

An entire new world is coming within the range of man’s vision. Its possibilities for adding to the health and happiness of mankind are almost limitless. The geographic poles have been conquered and the jungles of Africa traversed; and deep borings have been made into the bowels of the earth until heat has arrested further progress. The further exploration of both regions is of the utmost importance to the coming age. It is not at all visionary to assume that the heat of the earth’s interior in near time will furnish the power necessary to do the drudgery of mankind, give warmth and light to habitations, and operate transportation systems; and the New World Above offers pure, electrified, and highly stimulating air into which helium-inflated dirigible balloons will sail, and in which they will remain not only days but weeks or longer, with their multitudes of people.

While the use of kites and balloons in sending automatic meteorological instruments far aloft has revealed more of the wonders of this hitherto uncharted wilderness of cold and partial or total darkness than the general public is aware of, only the outer fringes of the mysterious regions above the clouds and the storms have been penetrated.

When the manufacture of helium, a noncombustible gas almost as light as hydrogen, becomes more general, as seems imminent in the United States, the dirigible balloon may successfully compete with the railroads in the carrying of long-distance passengers. The recent loss of over forty lives in England by the collapse of the dirigible ZR2 probably was largely if not entirely due to the explosion and fire of the hydrogen gas with which the ship was inflated.

A decade ago, in a number of Chautauqua lectures, the writer invariably was greeted with looks of incredulity when he prophesied that within ten years travelers of the air would take breakfast at the Waldorf-Astoria in New York and afternoon tea on the banks of the Thames. And yet the ocean already has been crossed by an aëroplane in continuous flight, and in the near future it is highly probable that aërial navigation will be safer than travel by rail or automobile. The hitherto inaccessible parts of the earth will be sailed over and closely scrutinized, while travelers enjoy the comforts that heretofore have been associated with Pullman service.

In 1862 the English meteorologist Glashier ascended in a balloon to about the same height as that attained by Major R. W. Schroeder, U. S. A., who achieved a more difficult feat when he flew in an aëroplane to over 36,000 feet. And at Dayton, Ohio, celebrated as the home of the Wright brothers, on September 28, 1921, Lieutenant John A. Macready, U. S. A., reached the unprecedented height of 40,800 feet. These are the extreme altitudes to which human beings ever have attained, but they are only the beginning of explorations into a vast and largely unknown and extremely cold region,—one in which darkness increases with elevation until at the outer limits of the atmosphere no illumination whatever exists.

The high eastward wind and 69° below zero encountered by Schroeder are conditions that already had been revealed by the work done at the research station of the Weather Bureau, at Mount Weather, Virginia, and at other stations in this country and in Europe, by the sending up of instruments unaccompanied by observers. Under the direction of the writer the Weather Bureau liberated numerous small hydrogen gas balloons in the Rocky Mountain region, to which were attached automatic instruments registering the temperature, pressure, and the hygrometric conditions. As they came eastward in the atmospheric drift that always prevails above the storms in the middle latitudes they attained to great altitudes, one balloon reaching 19.1 miles, the greatest altitude ever reached at that time by the appliances of man. Ultimately the balloons would explode as they expanded under the influence of decreasing air pressure and the case of instruments would descend slowly under a parachute designed to open at the right moment. The barometer traced a line on a paper cylinder revolving by clock works, as did the thermometer. The thermogram gave the temperature that corresponded with the varying elevation shown by the tracing of the barogram.

In 1898, twelve hundred observations were made with kites by the observers of the Weather Bureau at seventeen stations selected by the writer, during the six warm months from May to October. It was surprising to find the temperature often losing as much as fifteen degrees with the first thousand feet ascent during middays of extremely hot periods. The average decrease in temperature per thousand feet elevation for all stations for all times, and at all elevations up to 5280, was 4°.

For over five years kites were used nearly every day in the year at Mount Weather to carry instruments aloft to heights ranging from two to four and one half miles, and at times to keep the apparatus up during all hours of the day, so that a comparison could be made of the difference between day and night temperatures. There is but little difference between midday and midnight at only a few thousand feet above the earth.

Few are aware that the rectangular kite of the weather man was the forerunner of the aëroplane of the aviator. In 1903, while directing wireless experiments in the sending of messages at Roanoke Island, North Carolina, the writer saw the Wright brothers, or their representatives, lying flat upon the lower planes of what appeared to be Weather Bureau kites and gliding in the air from the top of the sand dunes. This was the beginning of real flight by man. The ingenuity of the Wrights transformed the weather man’s kite, strengthened it, took out the ends, hitched on a rudder, and when the petrol engine had developed sufficient power with a given weight, installed it, and flew.

In the future the meteorologist and the aviator will be closely associated. With a sufficient number of weather observations made by aviators simultaneously and well distributed over the United States it will be possible to construct a daily weather map on some high level—say the three-mile level—similar to the map now based upon sea level. The pressure, temperature, wind direction, clouds, and rainfall would be recorded and charted for the upper region clear across the continent. Three miles is about halfway to the top of cyclonic storms and probably in the region of greatest activity. More accurate forecasts would be possible by the study of this additional weather chart. This coöperation of the bird man and the weather man in studying the geography of the new air world will mark an epoch in meteorological science as far-reaching in its consequences as were the discovery of the barometer by Torricelli and the uncovering of the principles of the thermometer by Galileo, the former of which was not known until more than twenty-three years after the landing of the Pilgrims at Plymouth Rock. Thus swiftly does the mind of man to-day explore the hidden recesses of nature’s mysteries, and with each conquest carry itself to a higher realm of existence.

In the not distant future, more storm warnings may be issued by the Weather Bureau for ships of the air than for those of the sea, for the navigation of the air must play an increasing and important part in the coming activities of the world. Science is becoming so skilled in the harnessing of the forces of nature to man’s desires and in the development of mechanical appliances, that it is reasonable to anticipate the possibility that long-distance travel over land or ocean ultimately will be almost entirely confined to the air.

As the result of the explorations of the atmosphere made by the institution at Mount Weather there was ready for our fighting air men at the front, immediately on our entry into the World War, a fund of useful information concerning a region that but a short time before was entirely uncharted. The instruments carried by the exploring kites and balloons had keen scientific eyes and they recorded on clock-timed cylinders what they saw. Thus did the air pilot know much about the direction and the force of the wind that he would encounter as he rose, the altitude where he would pass above clouds, the degree of cold that he would encounter, etc. He was told that the temperature would fall about one degree for each three hundred feet of his ascent until he reached the top of the storm stratum at six or seven miles, and that if he could reach that altitude he would observe a most wonderful phenomenon: the temperature no longer would fall with gain in altitude; he would enter a cold but an equally heated stratum, without finding any temperatures lower than were encountered upon entering the region, which is always about seventy degrees below zero.

If the aërial explorer could stop his ship and keep it at an altitude of about one and one half miles for twenty-four hours he would be startled to find that the coolest time of the period was during the daytime, not during the night, as he had expected to find it.

In the future the traveler in the upper reaches of the atmosphere will carry oxygen and make the kind of air that he wishes to breathe, and he will properly protect himself against the cold of his new world, which he will find deficient in dust motes and doubtless entirely wanting in the bacteria of putrefaction and of disease. There will be no clouds to obscure his vision; no rain or snow. He will not often ascend above the region where there are not some dust motes to scatter and diffuse a part of the solar rays and give him at least a partial illumination.

Few persons are familiar with the simple problems of the air which have such important bearing on the distribution of man into realms above those he has been accustomed to occupy. They do not know that the northwest wind brings physical energy and mental buoyancy because it has a downward component of motion that draws air from above, where it is free of impurities, and where high electrification has changed a considerable quantity of its oxygen into ozone, in which condition it remains but a short time after reaching the lower potential near the earth’s surface. More people die under the influence of the south wind than under the influence of the north wind, because the south winds hug the surface of the earth and become laden with impurities and are lacking in electrical stimulation. When inventive man becomes more familiar with the ocean on the bottom of which he has heretofore lived, he will not wait for the north wind to bring down to him the beneficial conditions that always exist higher up; he will go after them and remain aloft as long as he desires to do so.

The further development of the dirigible balloon and the aëroplane are among the most important duties that the engineer of the future owes to civilization; and the meteorologist must establish the climatology of the vast untracked regions above the highest mountain peaks, for here man will largely disport himself in the time to come.

The writer agrees with the opinion of Major William R. Blair, formerly of his staff when he was the head of the U. S. Weather Bureau, but since the beginning of the World War the chief meteorological assistant of the Chief Signal Officer of the U. S. Army when he says:

“With reference to air travel in the future: the present stage of aircraft development seems to indicate that long non-stop traffic, both freight and passenger, in the air will be by means of lighter-than-air craft (balloons). These craft have much larger carrying capacity than any airplanes now designed and will travel across the continent over several prepared routes, stopping only at important centers on these routes to discharge and take up passengers and freight. It is believed that airplanes (heavier-than-air craft) will ply between these important centers and the outlying country about them, thus acting as feeders to the main route, over which the monstrous dirigibles will operate. Most transoceanic as well as transcontinental air traffic will probably be carried on in these large dirigible balloons.”

Lieutenant Colonel Henry B. Hersey, who served through the World War in the Aëronautical Service of the Signal Corps, U. S. A., and who also was associated with the writer in the management of the Weather Bureau, says:

“The fields of the dirigible and the air plane are separate and there is no conflict between the two. For light loads, great speed, and quick manœuvering, the airplane is supreme. For heavy loads, long distance, ability to remain in the air for great periods of time, the dirigible is the only air craft that can fulfill the requirements. Dirigibles will soon be in use which can start from Europe, sail over New York, and drop enough poison gas to kill thousands and make practically the whole city uninhabitable.”

CHAPTER IV
EARTH’S FOUR ATMOSPHERES

The earth has four important atmospheres and others of less importance. The principal ones are oxygen, nitrogen, vapor of water, and carbon dioxide, each comporting itself as it would do if the others were not present. There is space between the molecules of each gas, and therefore it is easily compressed. A doubling of its pressure reduces its volume one half.

Composition of Atmospheric Air. It is difficult for the mind to form a picture of the infinitely small molecules of the air. Let us therefore use terms and comparisons that will the more directly appeal to the human senses. First let us imagine each molecule enlarged to the size of a small grain of sand. Then with the molecules from one cubic inch of air transformed into grains of sand we could build a roadway ten feet deep and one hundred feet wide extending from New York to San Francisco. May one still further grasp the idea of the atom, many of which are required to make up the molecules? If so, the imagination has been stretched to its limits to enable the human mind to comprehend some of the simplest facts with regard to the wonderful fluid in which we live.

Sir William Thomson, afterwards Lord Kelvin, in endeavoring to give relative values that would appeal to the imagination, said that if a drop of water were enlarged to the size of the earth, the molecules of which it is composed would be no larger than cricket balls, and the smallest about the size of small peas.

More than a thousand years before the birth of Christ a great Phœnician philosopher believed that all matter—solids, liquids, and gases—was built up from infinitely small aggregations of atoms. The learned men of Greece enlarged upon his views but this philosophy passed into oblivion with the destruction of Rome and the coming of the Dark Ages, and it was not revived until about one hundred and fifty years ago. The ancients could not prove their theory, while we to-day can count the atoms and determine their size and motions; and, exceedingly small though they be, we no longer believe them to be indivisible in structure. On the contrary, we know that each atom consists of particles of positive and negative electricity. The negative electrons arrange themselves about a positive electron for a nucleus and, rotating about it as if it were a central sun with planets, constitute an atom. All matter reduced to the ultimate electron is precisely alike. The difference in matter is determined by the number of negative electrons that are attracted and held in place by the positive nucleus that is at the center of each atom of which a particular kind of matter is composed. Each of the ninety-two elements which we believe constitute the ninety-two different forms of simple matter has an atom with its own peculiar type of nucleus, which nucleus differs from those of the others only in the amount of positive electricity it contains. Thus hydrogen, the lightest of all gases, whose weight is taken as unity in measuring the magnitude of other gases, has a nucleus whose positive charge of electricity is only sufficient to attract one negative electron. The next element, helium, has a nucleus with a double positive charge and consequently holds two electrons or planets to pay it homage. In like manner the carbon atom contains six electrons; oxygen, eight; aluminum, thirteen; nitrogen, fourteen; sulphur, sixteen; iron, twenty-six; copper, twenty-nine; silver, forty-seven; gold, seventy-nine; mercury, eighty; lead, eighty-two; bismuth, eighty-three; radium, eighty-eight; thorium, ninety; and uranium, ninety-two. The chemical union of these elementary forms of matter creates other forms. For instance, the union of two atoms of hydrogen and one of oxygen constitutes a molecule of water. But the gases of the atmosphere are not in chemical union; they exist in the form of a mechanical mixture, each acting as though the others were not present.

It is important that this mixture of gases that constitutes our air be maintained in the right proportion. Only a slight difference in relative amounts might be disastrous to life. An increase in the oxygen would stimulate mental and physical activities and hold the human faculties at a higher tension. Man would accomplish more in a given time, but his span of life would be shortened; and too great an increase in the proportion of this stimulating element would quickly terminate life. Conversely an increase in the nitrogen would render all life more lethargic and man would be slower to act and to think; and too great an increase would smother every living thing.

In addition to the gases named, the air contains small amounts of many other substances,—argon, nitric acid, ammonia, ozone, xenon, krypton, and neon; as well as organic matter, germs, and dust in suspension. Over the land it contains sulphates in minute quantities, and over the sea and near the seashore salt left from the evaporated spray.

The proportion of each component of the atmosphere by volume of the total atmosphere is different from its proportion by weight. The percentages for the more abundant gases are as follows:

Nitrogen. Its principal functions are to dilute the oxygen and to furnish food to vegetation. It is inert and does not manifest many marked chemical affinities. Its lack of activity is shown by the fact that it will neither support combustion nor burn.

Oxygen. Oxygen, unlike nitrogen, is an active element that readily enters into chemical combination with many other elements, and it is second in quantity to nitrogen. With hydrogen it constitutes eight ninths, by weight, of water; combined with other elements it constitutes forty to fifty per cent. of the crust of the earth. It burns so readily that were it not greatly diluted by an inert gas like nitrogen it would be difficult if not impossible to stop a conflagration when once started. It is the vitalizing principle in all forms of life. By its chemical union with carbon in the tissues of plants and animals it develops the energy manifested in their movements.

In the free air up to about seven miles high there is no variation in the proportion of oxygen. But variations of marked importance to health and life occur in places where ventilation is restricted, and especially where living creatures exist in closed rooms, and where combustion occurs in confined places. The following variations in percentages by volume were found in careful analyses by Robert Angus Smith: On the seashore of Scotland, 20.99; open places in London, 20.95; in a small room where a petroleum lamp had been burning six hours, 20.83; pit of a theater at 11:30 P.M., 20.74; in a court room, 20.65; in mine pits, 20.14. He took samples from one mine that showed 18.27, the candles going out when the amount had decreased to 18.50.

The absorption of oxygen by putrid matter and by living beings in the process of breathing, and the giving out of carbon dioxide by both explain the deficiency of oxygen that is found over large cities, which is more marked when the air is moving but little and where the city is located in a depression or near swampy lands.

Both animals and plants inhale oxygen and exhale carbon dioxide with the unchanged nitrogen. The process automatically proceeds both night and day. It should not be confused with the opposite action of plants under the influence of sunlight in taking in and decomposing carbon dioxide and expelling pure oxygen.

Carbon Dioxide. It forms the chief food supply of all green-leaved plants. It is as necessary to the life of vegetation as is oxygen in the supporting of animal life. In the ratio of seventy-seven to one hundred there is less of this gas present in the atmosphere in the winter than in the summer; there also is a diurnal maximum and minimum. In the open country the amount averages about 0.035 per cent. by volume. In cities the amount is considerably greater, frequently rising to 0.07, and at times to 0.10 when the wind velocity is too low to scatter the excess amount that accumulates near the ground. Any quantity in excess of 0.06 per cent., especially if combined with the organic matter exhaled from the lungs and from the pores of the skin by animals and man, is injurious to health. Angus Smith found as much as 0.32 per cent. in crowded theaters, and 2.50 in mines. The latter amount soon would destroy animal life.

Vegetation, in addition to the inhalation of oxygen and the expiration of carbon dioxide at all hours, absorbs the latter during the day, and under the influence of sunlight the green granular matter that constitutes the chlorophyll of the cells of the leaves decomposes it, the plant retaining the carbon and giving out the oxygen. Because of the absence of sunshine the chemical activities of the plant are altered at night and the absorption of carbon dioxide ceases; therefore over the land the maximum amount occurs during the nighttime. This gas is dissolved in sea water and given off with a rise in temperature, which causes the maximum amount over oceans to occur at midday.

Carbon dioxide is 1.50 times as dense as an equal volume of atmospheric air. Its greater density causes it to collect in mines, sewers, cellars, and other low places, unless there is forceful ventilation.

The American cold wave should be welcomed as the mighty scavenger of the air. Its high velocity and great density cause it to search into cracks, crevices, sewers, and cellars and expel foul accumulations. How sweet and clean the air smells and how vigorous physically and buoyant mentally one feels after a rain and high winds! All nature smiles and every form of life adds its pæan of joy. Rain washes out the carbonic acid gas (carbon dioxide) from the air, with dust and other particles in suspension; and the cold wave enters our places of habitation and drives out the thieving accumulations of poisonous gases that would rob us of health and maintain conditions of morbidity.

It cannot be too forcefully stated that oxygen, the life-sustaining principle of the air, decreases, and carbon dioxide, a poison, increases in air that is breathed, or in air in which lamps or gas jets are burning; and that all places of habitation, especially sleeping rooms, should have a continuous supply of fresh air.

Water Vapor. It is only a little over one half as dense as atmospheric air. In the arid regions of the west it may form only a fraction of one per cent. of the air by weight; while in the humid regions in the eastern part of the United States it may constitute as much as five per cent. The temperature being the same, the same amount is required to saturate a given space, whether it be a vacuum or whether it be filled with air. Air doubles its capacity for water vapor with each increase of eighteen to twenty degrees. On a hot day in summer, near large bodies of water, it may constitute as much as one twentieth by weight of the lower air, while on a cold day in winter it may form no more than one thousandth part. When the air contains all the water vapor it can hold, it is said to be saturated; no more can be added to it until its temperature is raised, and but a slight lowering of its temperature will precipitate a part of its water vapor in the form of dew, frost, rain, hail, or snow. This is the reason it is usually called water vapor instead of a gas. Under the influence of heat that is below the freezing point, ice and snow may be changed from the solid to the gaseous form, and water vapor may be precipitated as frost or snow without passing through the liquid state.

The Dew Point is the temperature of saturation,—the temperature to which a body of air must be reduced before condensation can occur and some of its water vapor return to the liquid or solid state.

The Relative Humidity is expressed in percentages of the amount necessary to saturate. At a temperature of 32° air may continue to increase its vapor of water until it contains 2.11 grains per cubic foot, when it will be saturated and its relative humidity be one hundred per cent. If this same air be suddenly raised in temperature to 51° its capacity per cubic foot will be increased to twice what it was at 32°, the 2.11 grains will be equal to only one half the number necessary to saturate, and the relative humidity be expressed by fifty per cent. instead of one hundred per cent. In this way does the capacity of air for water vapor increase. Thus it is seen that the relative humidity of the air may increase during the cooling of nighttime without the addition of any vapor of water, and, in fact, with a decrease. The increase of relative humidity after nightfall is greater in the country than in the city, where the presence of pavements and brick buildings retards the loss of heat.

The Absolute Humidity is expressed in grains the cubic foot. The hygrometer is employed to measure the amount of water vapor.

Hydrogen is the lightest of all known gases. Its density in comparison with ordinary air is only .0692. It is combustible, and when five volumes of atmospheric air are mixed with two volumes of hydrogen the mixture explodes when ignited. It is supplied to the air by active volcanoes and in other ways, but the speed of its molecules is such that it readily escapes from the earth’s attraction and passes outward into space.

Ozone (Greek, ozo, I smell) is highly electrified oxygen, in which the molecules are broken up and reformed so as to contain additional atoms. It is formed by the disruptive discharge of lightning and by the great amount of electricity present in the high levels of the atmosphere, and possibly in minute quantities by the evaporation of fog and water near the earth. It is always found in the presence of waterfalls and spraying fountains. It is a powerful sanitary agent, readily entering into union with decaying matter. This fact accounts for the total absence of ozone from the air of large cities.

Ozone, in the minute quantities found in nature, is healthful, but when breathed in a condensed form it has a highly irritating effect on the mucous surfaces of the respiratory passages, and the quantity is not large that will cause death. The healthfulness of mountain air may be due largely to the increase with elevation in the quantity of ozone and electricity in the air, as well as to the less number of disease germs and dust motes. The invigorating effects of the crisp air of the frosty morning and of the cold wave in winter may be increased by the activities of ozone.

Ozone has two daily maxima, the principal one occurring between 4 and 9 A.M. The minima occur between 10 A.M. and 1 P.M., and between 10 P.M. and midnight. The winter furnishes an amount greatly in excess of the summer, due not only to the less amount of decaying matter to take up the ozone in winter, but to the higher and more persistent winds mixing the lower and upper air. The amount is greater over the sea than over the land, probably due to the absence of oxidizable matter, which allows the ozone to accumulate over the water. It is more abundant with westerly than with easterly winds, due to the fact that westerly winds have a downward component of motion; but if the westerly winds be weak and the easterly winds come from over a large body of water the conditions may be reversed.

Microbes of the Air. The air transports vast armies of unseen workers. Some are enemies; others are benefactors of the human family. The useful varieties are energetic in clearing away the refuse of animal and vegetable life, in fixing fertilizing gases in the soil, in giving flavor to fruits and proper growth to leguminous crops, in transforming the crudest must into the best claret, and the poorest tobacco leaf into the fragrant Havana; in curing cheese and butter and fermenting beer, and in a multitude of other useful employments. The malevolent varieties, if they gain lodgment in suitable human tissues before sunlight weakens their virility, disseminate certain forms of disease.

In picking a permanent place of abode, remember that there are many less disease microbes in the air of the open country than in that of the city, and that few are found in the air of mountains, or in that of the ocean. The average number of bacteria in a cubic meter of air in the city of Paris has been found to be 4790, while ten miles away in the country the number was only 345.

Accurate analyses of the air of crowded tenements always have shown large numbers of bacteria, but the number was found to be small in well-ventilated city houses that let in an abundance of sunshine to their interiors. It is better to have color in the cheeks of the occupants than in the furnishings of a house. Curtains and heavy drapery not only furnish a refuge for the microbes of disease, but they may be so hung as to exclude the purifying sunshine. The amount of sunshine is nearly as important as the quantity of air, for most of the microbes of disease quickly die, or are rendered less virulent, under its influence.

Bacteria exist in small numbers, if at all, at altitudes where snow forms, but snow gathers them as it falls through the lower air. Ice contains bacteria, but not in any such quantity as the water from which it freezes. Ice forms in the open at the surface of the water, or about numerous small particles of matter in suspension, which rise at once to the top as soon as the ice congeals about them in the form of a buoyant covering; meanwhile sediment is continually settling to the bottom, carrying bacteria with it. Ice forms more readily in quiet water, where sedimentation has been most rapid, and where, therefore, there are the fewest bacteria in position to be included. More disease germs exist in river water in winter than in summer, which may be due to the greater disinfecting power of the sun’s rays during summer.

Dust Motes of the Air. As the earth pursues its course about the sun, dust rains into its atmosphere from outer space. Meteors that are burned through the heat generated by striking into our air contribute to the supply, as do volcanoes, combustion, spray from the ocean, and matter lifted up by the action of the wind.

Dust from the eruption of Krakatoa was wafted entirely around the earth, falling upon the decks of ships in all the seas of the world. It affected the colors of the sky for two or three years after the explosion.

As in the case of microbes, the number of dust particles is far greater in cities than in the country, being least on high mountain tops and over the oceans. The air in large cities invariably shows hundreds of thousands of dust motes to the cubic centimeter, that of the village thousands, and that of the open country some hundreds. Dust-free air is also germ-free. Many experiments have shown that air freed of dust motes has at the same time been cleared of the microörganisms that cause disease, putrefaction, and fermentation; and that germ-free flesh or liquids may be indefinitely exposed in such air without fermentation or decay.

How Dust Motes Are Counted. Many of the particles are too small to be seen by the highest powers of the microscope, yet Aitken, by a most ingenious method of making them centers of condensation—that is, making them the nuclei of small raindrops—was able to count the number in a given volume of air. When ordinary air is saturated and then cooled the cloud formed is so dense that it is impossible to count the tiny droplets that form the cloud. But we can make the number of dust particles (and therefore the number of visible points of condensation) in a given volume of air as small as we wish by mixing a little dusty air with a large amount of dustless air, and we can allow the particles to fall on a bright surface and can count them by means of a lens or microscope. By simply allowing for the proportion of the dustless to the dusty air, and making a corresponding allowance for the dilution, we calculate the number of particles.

Dust Motes and Illumination of the Atmosphere. One of the most important functions of dust motes is the diffusion or scattering of sunlight. What a different world this would be without these tiny inanimate friends of man! If there were no dust in suspension in the air, nothing would be visible except what received direct light, or light reflected from some illuminated surface, and the air occupying space between illuminated objects would be practically dark. If the observer be in a room with a powerful electric light he would see the walls and the objects in the room, but if the air were free of dust motes, he would find that the space between him and the walls and between the various objects would be as inky black as is the space between the twinkling stars on a clear night.

Fig. 2.—Showing light from lamp a passing into dust-free air at b, and passing out at c without illuminating the interior.

[Figure 2] is a cubical box, with a glass front. If a glutinous substance be spread over the bottom and the box allowed to remain quiescent for from five to seven days the dust motes will slowly settle down and attach themselves to the bottom. The air then will be what is called “optically pure.” Now, if it be taken into a dark room and an inclosed lamp at a be allowed to send a beam of light into the window at b and out at c, it will be found that the interior remains dark no matter how powerful the light from the lamp. The light is seen to enter and to leave but where it encounters the dust-free air there is nothing to scatter the light rays and they remain invisible to the eye.

Dust Motes Prolong Twilight. The bending or refraction of light as the sun’s rays pass obliquely through the air at sunrise and at sunset displaces the apparent position of the sun, elevating it by an amount about equal to its own apparent diameter, so that one may see it and receive its light when geometrically it is entirely below the horizon. A little later in the evening and its rays fall upon the upper air too obliquely to be bent down to the earth by refraction; but darkness does not yet ensue, for the rays are scattered by the dust motes and possibly by the molecules of the gases and sent downward from particle to particle, resulting in a soft shimmering light that almost imperceptibly fades away, and which in higher latitudes may last for hours.

CHAPTER V
LIGHT, HEAT, AND TEMPERATURE

MORE WONDERFUL THAN ANY FICTION ARE THE FACT OF INVISIBLE LIGHT, AND THE DIFFERENCE BETWEEN HEAT AND TEMPERATURE

The heat that escapes from the earth’s interior is minute in comparison to that received from the sun, which is the main source of the earth’s supply. Heat is manifested by the motions of the molecules of matter, whether solid, liquid, or gaseous. It is transmitted through space in some mysterious manner, for space is practically void of an atmosphere. One cannot conceive of motion taking place in a void, for there is nothing to move. Therefore it is assumed that interstellar space must be filled with a transmitting medium; to this the name of ether has been given. Nothing is known of its structure, but it is believed that it penetrates all bodies and fills the space between their molecules.

How Heat and Light Reach the Earth. The heat of the sun is some forty-six thousand times as intense as is the heat of the earth. The violent agitations of the molecules of the sun’s hot atmosphere impart vibrations to the ether of space, which decrease in effectiveness inversely as the square of the distance; that is to say, that if the earth were twice as far from the sun as it is, the intensity of the solar rays would be one fourth of what they are now. These vibrations are called solar energy. They pass through space without perceptibly warming or lighting it. When they encounter the molecules of the earth’s atmosphere, and the dust and cloud in suspension in the air, or impinge upon the solid matter of the earth, they are transmuted back into molecular agitations, and manifest themselves in a multitude of forms, such as heat, light, chemical rays, electricity, etc.

The Difference between Heat and Temperature. The agitation of the molecules of a substance set up by the absorption of heat is indicated by temperature, which gives no measure of the quantity of heat absorbed, the quantity varying widely for different kinds of matter. The amount of heat necessary to raise one pound of water 1° F. is the heat unit generally employed in commerce; but in scientific research the amount necessary to raise one gram of water 1° Centigrade is the unit of heat best adapted to use. It is called the gram-calorie.

Let us take a glass filled with boiling water. You see the glass and the water because they reflect to the eye light waves received from some source,—possibly the sunlight that is diffused by the dust motes of the air into the room through the window. But the glass and the water radiate other waves to which the eye is not sensible; these invisible long heat waves may be felt by the nerves of the hand. They warm all matter upon which they fall by adding to the agitation of the molecules of which it is composed; but they do not warm all matter equally. The waves that reach dark bodies are broken up; that is to say, absorbed. Their energy is transmuted into sensible heat, and in the place of the waves we have molecular vibrations in the matter, which are made manifest by a rise in its temperature. Dark rough surfaces more completely absorb the waves and therefore rise to a higher temperature than the same surfaces when smooth. When the waves encounter bright and highly polished surfaces the effect is quite different; then most of them are reflected away and therefore warm the matter but little. These reflected waves are not broken up, but on the contrary start off in some new direction, possibly falling upon and warming some matter more receptive to their influence. The higher the polish the more completely are the waves reflected.

Difference between Light Waves, Heat Waves, and Sound Waves. The light and the heat waves of the ether are infinitesimal ripples as compared to the backward and forward pulsations that constitute the sound waves of the air. Within a space of one inch there are sixty-six thousand of the violet waves of light, which are the shortest etheric vibrations to which the human eye responds, and over thirty thousand of the red waves, the longest that affect the eye; while the sound waves of the air vary from about one foot for the shrill notes of the human voice to four feet for the middle C of the pianoforte. A shrill whistle produces waves of about one half inch. There are twenty-two thousand of certain heat waves to the inch, and these, like some of the light waves of the ether, are invisible.

There is also a vast difference between the velocity of vibration of the air waves and those of the ether. The human ear is sensitive to sound waves of somewhere between twenty-nine per second to thirty-eight thousand per second; while the eye responds to light waves of from five hundred million to one billion per second. Some ears are better adjusted to the low vibrations and some to the high, and the ears of no one hear any but a small part of the melody of a great symphony. Tyndall could hear the sharp chirp of thousands of insects that were inaudible to his guide as the two climbed the Alps, but the guide’s ears responded to the long, slow waves that came from the dull tread of the donkey’s hoofs farther up the mountain, which waves the scientist was unable to hear. Likewise some eyes are able to penetrate far into the violet, or the red, or both, and some are unable to distinguish between certain colors.

Chemical Rays of Light. The chemical or photographic rays have still shorter waves than the violet. They produce special physiological effects in vegetable and animal tissues, and, acting upon particular kinds of matter, they cause fluorescence, which is the property possessed by some bodies of giving off, when illuminated, light of a color different from their own and from that of the light that illuminates them. These chemical rays are sometimes called ultra-violet rays.

Invisible Light. From a reading of the immediately preceding paragraphs one may be prepared for the startling statement that there is such a thing as invisible light. Vibrations of the ether that move slower than those that give to the eye the sensation of red are invisible, as are those that move faster than the violet rays, and it is certain that neither the eye of man nor of animal ever will see but a small part of the beauty of a landscape or the delicate coloring of a flower. The eye only takes in and renders sensible to the brain the red, orange, yellow, green, blue, indigo, violet, and their various tints, but the delicate instruments of science reveal many other colors. One sees as through a glass darkly, for the gentle signals that might reveal the beauties of Paradise fall upon the eye unheeded. A keener vision and a more complete appreciation of the beauties and the wonders of the universe await one on the other side of the gauzy veil of immortality. The finger tips of the outstretched arms may span the river of life and the ethereal breath of loved ones may be caressing one’s cheek. The music of the spheres is not a myth; the lily or the rose as it opens its petals to receive the benediction of the morning sun may give forth a veritable pæan of joy. A rose bush may be a grander symphony than anything that Beethoven ever wrote. What to us is the invisible light may be the illumination that guides the sweep of the angels’ wings.

How Heat Moves through or Is Transmitted by Matter. Heat passes by contact from the warmer to the colder molecules of a body. This action is called conduction. When one end of a bar of iron is held in a fire, the end away from the fire soon becomes too hot to hold in the hand, because heat is rapidly transferred from the hot portion of the bar to the cooler portion by conduction, showing that iron is a good conductor. On the other hand, the end of a stick of wood can be held in the fire until it is completely consumed without the other end becoming too warm to hold, indicating that wood is a poor conductor. Metals are the best conductors, silver leading the list, with copper second. 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. When air or water is not evenly or homogeneously heated a circulation is set up in which the colder part settles down and the warmer rises. This is called convection. The air that is heated by contact with a stove rises and passes along the ceiling to the colder parts of the room, gradually parting with its heat until it is no warmer than the air next adjacent to it, and slowly settling to the floor as the cold air beneath it moves toward the stove, is warmed and sent aloft, the first air finally making a complete circuit and returning to the stove again. In this way the heat is distributed by convection throughout the whole room. When one part of the earth’s surface becomes hotter than another a similar action takes place on a large scale. The region of greater temperature warms the air above it, and the surrounding denser air flows in along the surface, forcing the lighter air to rise, when it in turn is similarly warmed and driven up.

The clear waters of lakes and rivers and of the ocean permit the passage of heat waves to a considerable depth before they are completely absorbed. On a cold day in winter, when the sun is shining brightly, a room with spacious windows may become as warm as though heated by a furnace, simply by the capacity of the glass in the windows to transmit the heat waves of the sun without considerable absorption, and at the same time prevent the escape of the longer heat waves that are radiated from the interior walls of the room. This capacity of matter to transmit heat waves without absorption is called diathermancy. The clear atmosphere is an exceedingly good transmitter, and rock salt is one of the best of all solids.

The capacity of a body to transmit light without absorbing it and becoming luminous is called transparency. Air freed of dust motes is almost perfectly transparent. In this state it is said to be optically pure. But the ordinary air of nature, with its moisture and dust, absorbs most of the blue wave lengths and also many of the longer ones of the other colors of the spectrum.

The capacity of a body for heat is called its specific heat. With but few exceptions the specific heats of liquids are much greater than those of solids or gases. It requires ten times the quantity of heat to raise a pound of water one degree that it does a pound of iron. Ice has the greatest specific heat of any of the solids, except paraffin and wood.

When a solid is melted or a liquid vaporized a large amount of heat becomes latent, insensible to the touch; it disappears as heat. This is one of the most wonderful of the phenomena of nature. It matters not how long the time may be, an hour, a day, a year, or a thousand years after the solid is melted or the liquid turned to vapor, so soon as the vapor returns to the liquid state or the liquid to a solid condition, the latent heat becomes sensible in exactly the same degree in which it previously existed. Let us illustrate with a pound of ice at zero F. Sixteen heat units, or sixteen times as much heat as is required to raise one pound of water one degree, must be absorbed by this pound of ice to raise its temperature to the melting point (32°); and then one hundred forty-four more heat units must be absorbed to so far overcome the tendency of the molecules to adhere, or remain together, that the molecules may roll the one about the other in the liquid form, but with this important difference: the one hundred forty-four units become latent and do not, therefore, cause any increase in temperature, as the sixteen heat units did in raising the temperature of the ice. The large quantity of heat required to change the ice to a liquid is called the latent heat of melting. Any further addition of heat after the melting is complete causes an increase in temperature, and one hundred eighty heat units will raise it to the boiling point. Water boils at 212° at sea level and normal pressure; that is to say, at that temperature the agitation of the molecules of water is so great as to overcome both cohesion and the weight with which the air presses down upon them, and cause them to fly away in the form of steam, which is invisible when confined inside a boiler. But the entire pound of water is not instantly changed to the gaseous condition, for with the sending off of the first few molecules some heat is rendered latent, and more must be supplied or the boiling ceases; in fact the enormous quantity of 964.62 heat units must be supplied to entirely change the pound of water to steam, but at no time does the temperature rise above 212°. As in the former case of changing the solid to a liquid, a large amount of heat becomes latent; in this case it is called the latent heat of vaporization.

Now carefully fix in the mind that a liquid does not need to be raised to its boiling point before vaporization begins, for it operates at all temperatures, even after the liquid is frozen, but much more rapidly from the liquid. If one wishes to test this: weigh a piece of ice during very cold weather. Then leave it out in a temperature that is below freezing for several days, and on weighing again it will be found that the ice has lost weight. All evaporation produces a cooling effect because of the heat that is rendered latent in the process of changing the liquid or the solid to a gaseous form. The drier the air the greater is the cooling effected by keeping the surface wetted, and the cooling is accelerated by placing the wet object where there is a free circulation of air.

A wooden water bucket that has been soaked for a day or two so that every part of the wood is saturated with water, will, if kept closed, keep water all day in the open field practically as cool as when it left the deep well, and often cooler. Not enough use is made of cooling by evaporation by those who have not ice in the summer. Inexpensive and fairly effective refrigerators may be made, by any mechanic, of lattice-work sides covered with any thick fabric and kept moist, which would keep milk, butter, fruit, vegetables, and cooked meats in good condition if placed in a hallway with a good circulation of air, or in any shady place with good ventilation.

Most solids expand with gain in temperature and therefore possess greater volume in the liquid form than in the solid, and the temperature of their melting points rises as they are subjected to increasing pressure. The law reverses when applied to ice, which contracts in melting. To few is it known that a skater on ice really rides upon water molecules, for the sharp edge of the skate, when applied to the ice under the weight of one’s body, is lubricated by the slight melting of the ice in immediate contact with the skate, the molecules of water returning to the form of ice as soon as the skater passes and the pressure is relieved. The strange phenomenon may be witnessed by passing a wire through a block of ice without severing it into two pieces, by attaching heavy weights to the two ends of the wire and suspending it across the ice, the ice slowly melting as the result of the pressure applied by the underside of the wire and freezing molecules closing the space on top of the wire. By this process do we account for the moving of glaciers down tortuous valleys as though they were liquids.

Altitude Measured by Change in Boiling Point of Water. The boiling point of water at sea level and ordinary air pressure is 212°. If the pressure of the atmosphere were increased to about thirty pounds, instead of about fifteen to the square inch it would be necessary to raise water to 250° before boiling would begin. The changes of air pressure due to the passage of the severe storms of winter may cause the boiling point of water to vary from 207° to 215°. This knowledge may be useful in measuring the heights of mountains, although the method does not give close results. The decrease of pressure with altitude lowers the boiling point, the amount being approximately one degree for each 555 feet of ascent. The best results may be secured by having a person at the base of the mountain, where the elevation above sea level is known, determine the boiling point at the same time that a person on the mountain top does. The thermometers should be read closely to the fraction of a degree.

With the barometer at its normal height of thirty inches, air at 60° will instantly rise to the phenomenal temperature of 175.50 if it be confined and its pressure doubled, and it will diminish to one half of its former volume. But if its pressure be diminished one half, its volume will expand to double its original size and its temperature will fall from 60° to 2.4°. From these facts the reader would naturally expect to find low pressure of the atmosphere accompanying cold waves and high pressure to be coincident with warm conditions, which is exactly the reverse of what actually occurs in the free air of nature. This apparent contradiction will be made plain in the treatment of cold waves, [page 124].

A temperature of -459° on the Fahrenheit scale and -273.1° on the Centigrade represents what is called absolute zero. It is supposed to be the temperature at which there is no motion of the molecules of matter. Bodies or planets without atmospheres have temperatures approaching absolute zero, for there is no protecting envelope to absorb heat or to prevent the instant radiation into space of that which impinges upon the body. Our moon is an illustration, and notwithstanding the fierce beating upon its surface of the solar energy it remains incased in the intense cold of space.

The thermometer is the instrument that measures temperature. It was not until eighty-seven years after Columbus discovered America that Galileo discovered the principle of the thermometer. This first instrument was crude. It consisted of a glass bulb, containing air, terminating below in a long glass tube, which dipped into a vessel containing colored water. When the temperature fell the contraction of the air in the bulb caused the water to rise in the tube, and when the temperature rose the expansion of the air forced the water to a lower level. Galileo also invented the alcohol thermometer in 1611, but the determination of the zero and some fixed point above it, by which to graduate the scale, took years to evolve. The modern alcohol and mercury thermometers consist of a bulb filled with the liquid, and a tube partly filled, the upper part being a tolerably complete vacuum, allowing the liquid freedom of movement up and down the tube. When a tube is broken one is surprised to see that the diameter of the bore is less than that of the smallest fuzzy hair from the back of the hand. The size of the column of mercury is magnified by the action of light passing through the glass of the tube.

Temperatures are usually taken in the shade. The instrument should be free from all bodies that could conduct heat to it, and it should have free circulation of air about it.

In a complete meteorological station automatically recording instruments, too complicated for the use of the layman, record for each moment of time the temperature of the air and its pressure, the periods of sunshine, the duration and the amount of rainfall, and the direction and velocity of the wind.

CHAPTER VI
THE ADVANTAGE OF TAKING WEATHER
OBSERVATIONS AND APPLYING THEM TO
ONE’S PERSONAL NEEDS

FORECASTS MADE FROM THE ANEROID BAROMETER—COLDS PREVENTED BY MOISTENING AIR IN LIVING ROOMS—A CRIMINAL HANGED AND AN INNOCENT MAN FREED BY WEATHER RECORDS

Observations from Kites. It is strange that the Chinese, who have been flying kites many thousand years, should not have made improvements in the primitive construction of these devices. It remained for Wendham, in 1866, to perceive the advantage of superimposing two or more planes, one above the other, for the purpose of securing a larger area of sustaining surface. After examining [Figure 3] almost any one can build an efficient kite. Heights of two to three thousand feet may be reached by using cable-laid twine No. 24, but in order to gain great altitudes pianoforte wire must be used. Soft pine is the best and most available material. Spruce is stronger, but more difficult to secure. The sticks should be straight-grained. The cloth may be silk or the stronger and finer grades of cotton. It should be torn, not cut. The ends will then be true and square with the fiber of the cloth. Kites are used not only to secure weather observations, but they have been used to draw sleds in the Arctic region, and to draw wagons and boats. By adjusting the points at which the pulling cords are attached to the boat an ingenious sailor is able to proceed nearly at right angles to the direction of the wind.

Fig. 3.—Standard Weather Bureau Kite.

When it is known that a box kite having only sixty square feet of sustaining surface, flying at a considerable height, may lift a person of ordinary size, one is impressed with the idea that vessels of commerce might employ kites of large dimensions to increase the speed of sailing ships. The kites would fly in a stratum whose velocity is not restricted by friction with the surface of the water.

To launch a kite: run out about one hundred and fifty feet of the cord or wire while the kite is held by an assistant, who should give the kite a toss upward in the direction in which it must go. It is important that it be cast off directly in line with the wind. If the wind is light it may be necessary to run a short distance with a long line out in order to effect a launching.

Voluntary Weather Observers. There are more than three thousand voluntary or coöperating observers in the U. S. Weather Bureau. They receive no compensation other than the publications of the Bureau. They are required to read their instruments but once each day, as maximum and minimum thermometers record the highest and the lowest temperatures since they were last read and set. About sunset is the most satisfactory time for making the readings, since the thermometers will then show both the extremes for the past twenty-four hours. As a rule but one voluntary observer is accepted for a county. They are furnished without charge with maximum and minimum thermometers, instrument shelters and rain gauges, but not with wind vanes, anemometers for recording direction and velocity of wind, or barometers. But those who desire to become expert in forecasting the weather, as all may who study the chapter on forecasting, should equip themselves with an aneroid barometer, so that they may note the changes in the pressure of the air.

Fig. 5.—Comparison of the Thermometer Scales.

COMPARISON OF THERMOMETER SCALES

A little study of the accompanying information and diagram will enable any one to form a clear idea of the various thermometer scales and to convert temperatures from one scale to another.

Table of fixed points.

Only Fahrenheit and Centigrade scales are in general use, and the accompanying plate is designed to enable observers to convert temperature readings from one scale to the other without resorting to a mathematical formula.

For accurate and precise reductions between the different scales the following rules should be used:

1. To convert Fahrenheit to Centigrade: Subtract 32 and multiply by five ninths.

2. To convert Centigrade to Fahrenheit: Multiply by nine fifths and add 32.

3. To convert Fahrenheit to Reaumur: Subtract 32 and multiply by four ninths.

4. To convert Reaumur to Fahrenheit: Multiply by nine fourths and add 32.

5. To convert Centigrade to Reaumur: Multiply by four fifths.

6. To convert Reaumur to Centigrade: Multiply by five fourths.

An instrument shelter ([Figure 4]) is employed to screen off the direct and reflected sunshine, and to keep the thermometers dry. This shelter is a box with louvered sides, constructed in such form that there is a free circulation of air through it. It should be exposed in an open space as far away from buildings as may be convenient, or on a housetop, and be as free from shadows as possible. If such position cannot be secured, then place it on the north side of a building.

Fig. 6.—Dry and Wet Bulb Thermometers.

Comparison of Centigrade and Fahrenheit. Only Fahrenheit and Centigrade are in general use. [Figure 5] is designed to enable observers to convert temperature readings from one scale to the other without resorting to a mathematical formula. For precise reductions the following rules apply:

To convert Fahrenheit to Centigrade: Subtract 32 and multiply by five ninths.

To convert Centigrade to Fahrenheit: Multiply by nine fifths and add 32.

Humidity Affects Health and Complexion. The importance to health of maintaining a proper humidity in living quarters during the winter months and during all months in the arid and semi-arid regions of the West is not fully appreciated. Each habitation should be supplied with one to several hygrometers (Fig. 6), and frequent readings should be taken of the dry and the wet bulb thermometers so as to be familiar with the conditions under which one is living.

RELATIVE HUMIDITY TABLES

Temperature Readings in Degrees Fahrenheit. Relative Humidity Readings in Per Cent.
Barometric Pressure 29.0 inches.

RELATIVE HUMIDITY TABLES—Continued

Temperature Readings in Degrees Fahrenheit. Relative Humidity Readings in Per Cent.
Barometric Pressure 29.0 inches.

RELATIVE HUMIDITY TABLES—Continued

Temperature Readings in Degrees Fahrenheit. Relative Humidity Readings in Per Cent.
Barometric Pressure 29.0 inches.

A relative humidity of between sixty-five and seventy per cent. should be maintained in all living and sleeping rooms, if one is to escape colds, catarrh, and possibly pneumonia. Some nervous disorders are aggravated if not actually caused by the dryness of the air in steam and other heated apartments during the time that the windows are closed in cold weather. The vanity of the female sex is appealed to with the statement that nothing is more essential to securing and preserving a good complexion than the maintaining of a proper humidity in one’s own room. Efficient and simple and inexpensive humidifiers are now coming on the market. They are almost as necessary to the health of a household as stoves and furnaces. Often a right degree of moisture can be created by leaving clean water in the bathtub and in all wash basins and sinks. One may be surprised on taking humidity observations to find how quickly it increases in rooms two or three removed from the bathroom after water is run into the tub, and especially if the shower spray is turned on and allowed to operate for a few minutes.

In cold weather we maintain the aridity of the Sahara Desert in our hot, steam-heated apartments, with a relative humidity of less than thirty per cent. Is it any wonder that when we step from this atmosphere into the cold outside air, with a humidity of seventy per cent., the violent change is productive of harm, particularly to the delicate mucous membranes of the upper air passages, which have been irritated and their powers of resistance weakened by the dryness within? The period of pneumonia is the season of artificial heat in living rooms—or, more properly speaking, the period of indoor desert aridity.

Save Fuel by Moistening Air. If a room at 68° is not warm enough for any healthy person it is because the humidity is too low, and water should be evaporated to bring the moisture up to sixty-five or seventy per cent. of saturation. Water instead of coal should be used to make rooms comfortable when the temperature has reached 68°. Ten to fifteen per cent. of fuel could be saved in the heating of places of habitation if the air were properly and healthfully humidified. The reason for this is that if the air is dry the heat passes through it and warms it but little. Moisture stops the radiated heat that would be lost, absorbs it, and holds it at the place where it is needed. It has precisely the same effect as a soft wool blanket wrapped about the body of each person. The dry air permits such a rapid evaporation from the human body that one may actually feel colder with a dry air heated to 75° than in a moist air at 66° or 68°. Water is cheaper than coal, and in this matter much more healthful.

The cooling effect produced by a draught does not necessarily arise from the wind being cooler, for it may be actually warmer, but arises from the rapid evaporation it causes on the surface of the skin. Vapor of water forms a blanket about the earth and prevents it from scorching during the day and freezing during the night.

How to Forecast Weather with Only an Aneroid Barometer. No one except an expert observer should use the mercurial barometer. The aneroid will answer as well for the purpose of forecasting from a single instrument; it is cheaper and less complicated. First learn your elevation above sea level; then add to the observed reading of your instrument .10 for each one hundred feet elevation. Note the fall or rise and the direction of the wind and with the aid of the table on [page 76] highly satisfactory forecasts may be made by any intelligent person. Skill will come with practice. Write down your forecasts each day as you make them and the following day note in a blank space left for the purpose the success or failure of your effort. Thus will you profit by your mistakes.

As a rule winds from the east quadrants and falling barometer indicate foul weather, and winds shifting to the west quadrants indicate clearing and fair weather. The rapidity of the storm’s approach and its severity are indicated by the rate and the amount in the fall of the barometer. This applies to the Mississippi Valley and eastward to the Atlantic Ocean. Conditions are different in the Rocky Mountains, on the plateau of the mountains, and on the eastern Rocky Mountain slope, where precipitation seldom begins until after the barometer begins to rise after a fall, and the winds have shifted to the northwest.

Keep in mind that storms are great atmospheric eddies drifting from the west, with the winds blowing cyclonically toward the center; that when your wind is northeast the center of the storm is southwest of you; that when it is east the center is west; when it is south the center is north; when it is southwest the center is northeast, and when it is west or northwest the center is east of you.

Difference between Weight and Pressure of the Air. Air at sea level and at 32° temperature weighs one and one third ounces per cubic foot. A room twenty by twenty by ten feet contains some 333 pounds of air. The pressure of the air is a quite different thing. It is the sum of the weights of all the cubic feet of air that are stacked up, one on top of the other, clear to the top of the atmosphere. This is why the higher one goes, the less the pressure of the air, because there are a less number of cubic feet above. And then each cubic foot weighs a slight fraction less than the one just beneath it because the air has expanded. The room afore-mentioned sustains a pressure of 5880 on its floor and a like pressure on its ceiling, and a half of this pressure on each of the sides of the room. The room does not collapse because the air exerts a like pressure on the outside of the room and the two pressures are equal—one inward and the other outward.

Fig. 7.

—Mercurial Barometer. The glass tube on right is filled with mercury. With the thumb over the open end, it is reversed so that its open end rests under the surface in a basin of mercury on the left, and the mercury in the tube falls to n, at which point it is sustained by pressure of the air on surface of the mercury in the basin.

The Principle of the Barometer. In 1643 some Florentine gardeners found that they could pump water only thirty-three feet high. This is because the entire volume of air, if it were compressed to the density of water, would equal a covering around the earth of that depth. When the gardeners first began to work the plungers in their pump up and down they did not get water; it was necessary for them first to pump out all the air in the pipe leading down to the water in the well; then the water rose into the vacuum thus created, and it rose to a height that just balanced the weight or pressure of the whole body of air that rests upon the earth. Now, if the atmosphere surrounding the earth could be reduced to the density of mercury it would equal a covering only thirty inches deep; this is why the mercury normally stands at thirty inches high in the vertical vacuum tube of the barometer. ([Figure 7].) In the complete barometer a graduated scale is attached so as to measure the fluctuations in the height of the mercury. If one were to ascend in a balloon it would be found that the mercury would steadily fall with increasing altitude, until at eighteen thousand feet one half of the atmosphere would be left below and the instrument would read only fifteen inches instead of thirty. In ascending to the top of the Washington Monument, 555 feet, the pressure of the air decreases over one half inch.

The barometer rises and falls with the passage of storms because wind movement displaces air and causes it to accumulate at some places and become deficient at others, but in order to compare barometers exposed at many different elevations with the view of determining the geographic position of storm centers—of cyclones and anti-cyclones—it is necessary to reduce all barometric readings to sea level.

Weather Records Turn the Scales of Justice. How trivial the incident that may change the whole course of a lifetime and lead to peace and happiness or to discord and sorrow! Likewise the parting of the clouds and the coming through of the sunshine, or the moment of the beginning of rainfall, or the amount of rain that falls within a given time, or the direction of the wind, or the velocity of the wind, or the temperature of the air, or the depth of the snowfall literally thousands of times has furnished the evidence in courts of law that has turned the scales of justice in civil suits involving large sums of money, and in criminal cases where a prison sentence or the hangman’s noose threatened the defendant.

For illustration let us say that a ship breaks from its mooring, crashes into another ship in the harbor and sinks it. If the force of the storm is no greater than has previously occurred in that harbor, the first ship is liable for the loss of the second ship. But if the automatically recording instruments of the Weather Bureau show that at that time the velocity of the wind was greater than ever had been known before, then the loss is due to “an act of God” and the ship that broke her mooring is not liable for damages to the ship that was sunk, provided proper provision was made for such velocity of wind as reasonably might be expected to occur with the passage of a storm.

To cite a case that actually occurred: A railroad company was sued for the loss of a million dollars’ worth of lumber that was burned, as alleged, by sparks from one of its locomotives. Here came in the wind records of the Government and proved that at the time of the starting of the fire the wind was steadily and forcefully blowing in a direction opposite to what would carry the sparks to the lumber, and the company was protected against an unjust verdict.

Again heavy rain fell in excess of the capacity of the sewers of a city to carry away the water, and private property was damaged by the flood. In this case the city was compelled to pay for the damage to property, because the records of the Weather Bureau showed that previous rainfalls had been of equal or greater amount in the same period of time, and the city should have constructed its sewers of sufficient capacity to carry away such precipitation as experience showed was liable to occur.

The writer was once an expert witness in what then was a famous case. The defendant, a young and handsome woman previously of unimpeachable character, was being sued for divorce. Two witnesses swore that they had seen her come to an open window, facing south, at seven o’clock in the morning, in a house in which she should not have been, stand for several minutes looking into the garden upon which the window faced, clad only in her night robe. Unfortunately the woman was not able to establish a satisfactory alibi for the morning in question, and she stood facing a terrible calamity with no power to establish her innocence. Her accusers had given as a reason why she stood so long at the open window that the morning was warm and balmy. But, fortunately for the innocent woman, the weather records came to her defense when her case seemed hopeless and her life was about to be blighted with a scandal from which she never would be able to free herself, and proved that at the very time when she was supposed to have been standing in the open window a torrential rain was falling and a wind of fifty miles per hour was beating upon the outside of the window panes. The woman was acquitted and one of the witnesses spent several hundred balmy mornings behind prison bars.

At another time the writer came into a case where a robber had shot and killed a citizen who surprised him in the committing of his crime. The robber was on trial for murder and his lawyers were attempting to clear him by the introduction of evidence to prove that the day was so foggy that the State’s witnesses had blundered and seized the wrong man when they chased the murderer around a corner. The weather expert destroyed the only evidence that tended to raise a doubt in the mind of the jury as to the man’s guilt, by testifying that fog could come to the surface of the earth only when the air was abnormally light and the wind calm or only gentle; while at the time of the murder the barometer was unusually high and the wind brisk. Here again the meteorological records aided in vindicating the right, and secured the conviction and execution of a brutal murderer.

A remarkable case was that in which a tramp was being tried for the murder of a miserly old woman who was believed to carry a large amount of money about her person. The tramp came to her door and asked for food. She took him in and fed him and soon thereafter he was seen hastily to leave the house. An hour after he had gone the woman was found murdered and her clothing rifled. The tramp was overtaken, found to have a large amount of money of small denominations in his pockets, indicted, and placed on trial. The principal witness for the State was a man who was repairing a frozen water pipe in a trench by the side of the house opposite to that by which the tramp entered and left. He saw the blow struck, ran in fear to his home, and then informed the police. In explaining how he came to see the criminal act, he testified that he climbed out of the trench to get a drink from a bucket standing near by, and as he raised the bucket his eye came in line with a window of the house, through which he witnessed the murder. The case seemed clear against the tramp, as other witnesses had seen him enter and leave the house and positively recognized him. Just here his lawyer asked the trench digger how long the water bucket had been sitting by the side of the trench. The latter said it had been there from 7 o’clock until 10. Then the weather records came in to confound the falsifier and to vindicate innocence, for the automatic tracing of the pen that records every movement of the temperature proved that the temperature had not been above zero any time during the three hours that the bucket had been exposed and that it contained a solid chunk of ice if it contained anything. The trench digger then confessed that he himself was the murderer. He had seen the tramp enter and leave and thought it a favorable opportunity to commit the crime and put the evidence on another.

CHAPTER VII
FROST

There is nothing in the study of the atmosphere that so intimately concerns the horticulturist and the gardener as knowledge of the conditions under which frost forms, and the methods that may be pursued to gain immunity from its disastrous effects, or to lessen the loss.

Frost does not necessarily form from air that has fallen to the freezing point, as many suppose. On the contrary, the air ten feet or less above the vegetation may be several degrees above freezing when there is a heavy and destructive frost upon vegetation. The fact is that vegetation radiates heat towards a clear sky faster than does the air and may fall to the freezing point or below; while the air, except the molecules actually in contact with the vegetation, is considerably warmer. Frost is not frozen dew. The water vapor is precipitated, or rather congealed, upon the vegetation without passing through the liquid state at all. Frost is spoken of as light, heavy, and killing. Tomato plants are killed by only a light touch of frost, while fruit blossoms will stand several degrees of cold below freezing. Therefore the tomato grower would consider as killing a frost that to the fruit grower would only appear as light.

The radiation of heat from the earth is continuous both day and night when there are no clouds to obstruct the passage of the heat rays. The amount received from the sun during the day is greater than the loss by radiation from the earth and the temperature of the air rises. After the setting of the sun the radiation of the earth goes on but there is no incoming heat from the sun to offset the loss and the temperature of the air falls. As previously stated, the soil and vegetation radiate faster than the air and the air in immediate contact with the soil is cooled by conduction to it. Thus over a level plain on a clear calm night there is found a relatively thin layer of cold air near the ground, which increases in temperature up to two hundred or three hundred feet, or which may be only five or ten feet deep. Over sloping ground the force of gravity tends to cause this thin surface layer of cold air to move down the slope and to gather in depressions in somewhat the same manner as water would move. Such movement is called Air Drainage. Of course this air is slowly gaining heat by compression as it passes to lower levels, but it is hugging closely to the cold earth and losing by conduction much or all that it thus gains by compression.

After a study of the contour of the region with respect to air drainage the writer purchased a considerable tract of land near Rockville, Montgomery County, Maryland, and planted extensive orchards thereon, with the result of harvesting nine successful crops of fruit in a period of ten years after the trees became large enough to bear. With the composition and the surface covering of the soil the same, the low places in a field are always the ones that suffer most when frost is possible. [Figure 8] shows a minimum temperature of 25° to have occurred at the base of a steep hillside when on the higher ground at an elevation of but fifty feet the lowest temperature was 44°, and at two hundred and twenty-five feet up the mountainside the minimum was 52°.

Fig. 8.—Continuous records of the temperature from 4 P.M. to 9 A.M. at the base and at different heights above the base of a steep hillside, showing the great differences in temperature that sometimes develop on a clear, still night. Although the temperature at the base was low enough to cause considerable damage to fruit, the lowest temperature 225 feet above on the slope was only 51°. Note that the duration of the lowest temperature was much shorter on the hillside than at the base.—Weather Bureau.

In selecting a location for an orchard it is not so much a problem of elevation above sea level as elevation above the surrounding region. The direction in which the slope faces makes little difference. The prime consideration is to get sufficient air drainage to gain the greatest protection against frost without selecting land with such a steep slope as to furnish excessive soil drainage and which would be difficult to cultivate and move about upon in the spraying of trees and in the picking of fruit. In the Maryland orchard the elevation was only five hundred feet above sea level and only about two hundred feet above the surrounding region, and the slope was so gradual as almost to be imperceptible to one passing over it.

After nightfall the air on mountain peaks and on hills and ridges soon becomes cooler than the air at the same elevation out over the open valley, due to contact with the elevated earth, which radiates heat and cools faster than the air.

Water vapor has a great capacity for heat. It is the most effective of the various gases present in the atmosphere in obstructing radiation of heat from the earth, as well as in absorbing incoming radiation from the sun. The night temperature, therefore, falls more slowly when the relative humidity is high than when it is low, that is to say, when the air is nearer saturation, or nearer its dew point. Drops of water that collect on the outside of a pitcher of ice water on a warm day are formed through the chilling of the air in contact with the pitcher; they begin to form as soon as the temperature of the pitcher reaches the dew point of the air, which temperature varies in accordance with the amount of water vapor present in the air at the time. After sundown the temperature of exposed objects falls, of some faster than others, depending on their capacities for radiation. Vegetation radiates freely and often falls to the dew point of the air, at which time dew begins to form on it and continues to be deposited as long as the temperature remains above freezing. Now, here carefully note that if the dew point is above 32° the condensation of water vapor in the form of dew liberates latent heat, which usually will be sufficient to check the fall of temperature and prevent the formation of frost. If the dew point of the air is 32° or lower frost forms. If the dew point is very low the temperature may fall low enough to cause much damage without the formation of any frost. As an example, if the dew point be 20° and the temperature falls to 24° much damage might be done to growing crops and no frost appear. This phenomenon is called black frost; it seldom occurs. From the foregoing it might be assumed that the possibilities of frost might safely be forecast from an observation to determine the relative humidity taken early in the evening, but unfortunately experience has shown that reliance cannot be placed in such method of forecasting, as the humid air of early evening may be displaced by much drier air before the hour of minimum temperature the next morning.

One of the best locations to gain immunity from frost at the critical period of plant growth is immediately to the leeward of a considerable body of water. Wind blowing from a large body of water is always heavily laden with moisture, which decreases the rate of radiation both day and night, but especially during the period of cold in the early morning when frost is liable to occur. Such winds, largely affected by the temperature of the water over which they have passed, modify the temperatures of both day and night.

The all-important condition for the formation of frost is an atmosphere already cool, with a gentle northwest wind and a clear sky, which condition, with more or less coolness, always accompanies the high barometric areas that follow the low-pressure areas of warmth, cloudiness, and moisture.

At an expense of two millions of dollars per annum the Government maintains some two hundred observation stations of the Weather Bureau, and twice daily telegraphs observations to all the large cities of the nation, but unfortunately in many cases these are not published for the benefit of the people who could make valuable use of them. The Bureau’s own deductions from these observations, in the form of forecasts and warnings, are extremely valuable, but an even greater service could be rendered the public by neatly lithographing an evening weather map and mailing it from all large cities each night, so that every intelligent person whose business is affected by the weather could, through a study of the chapter on Forecasting in this book, judge for himself as to the effect that the coming weather may have on his particular interests. One could then watch the movements of the high barometric areas and the low areas and become weatherwise himself, and he who studied these charts the most diligently would have an advantage over less progressive competitors.

Evaporation goes on at all temperatures, even below freezing and from solid ice, its rate, of course, being diminished by low temperatures. At times, in spring or fall, the temperature of the air over rivers, when there is little wind, falls so far below the temperature of the water that the water vapor rising from the river by evaporation is quickly condensed in the form of fog, which may cover a part or all of the low contiguous land, checking radiation and preventing a further fall in temperature.

In valleys near the ocean, fog sometimes drifts in from the water when frost is imminent and prevents its formation. On nights with fog, contrary to the usual condition, the hillsides are always colder than the lowlands, unless the fog extends high enough to cover them.

In 1891-1894 the writer, in studying the conditions under which frost forms on the cranberry bogs of Wisconsin, was impressed with the fact that the occurrence of frost on a given field depended as much on the character of the surface and its covering as it did on the temperature of the air a few feet above, one place receiving an injurious frost, another a light frost, and still another none at all, while each had the same conditions as to temperature, wind velocity and direction, and all were at the same elevation, so that the differences could not be accounted for by air drainage.

In one case the marsh was cleanly cultivated and covered with sand, in another there was clean cultivation but no sand, and in still another case there was a thick growth of vegetation. As the result of a long series of observations conducted by Professor H. J. Cox, working under the directions of the writer, minimum thermometers were placed among the vines over newly sanded surfaces in two marshes, one at Cranmoor and one at Mather, Wisconsin. The locations selected for this inquiry represented the best results that could be secured from sanding, draining, and cultivating. Comparison was made at each marsh between the readings taken close to the vines of the clean part of the marsh and those taken close to the surface over the unsanded peat bog. The average lowest night temperature over the sand for the four months was 5.9° higher than over the peat at Cranmoor, and 4.2° at Mather. On one night the minimum over the surface at Cranmoor was 12° higher than over the peat, while at Mather a difference of nine degrees was recorded on another night.

Through cultivation the marsh may be kept free from weeds, moss, or other rank growth, thus permitting the sun’s rays to reach the soil and increase its temperature during the day, while a growth of thick vegetation screens the soil from the sun’s rays, and there is consequently less heat in the latter soil to be given out during the hours of low temperature at night. Drainage lowers the specific heat of the soil and decreases the cooling effect of evaporation. Therefore, under sunshine, the dry soil becomes warmer than the wet and, whether or not it has a greater quantity of heat to give off at night, it has a higher temperature and therefore radiates more freely to the air above. A covering of sand likewise lowers the specific heat of the surface and thereby causes it to gain a higher temperature during the day than an unsanded surface receiving the same solar rays. It therefore radiates more rapidly at the critical time when heat is needed to prevent the temperature of vegetation from falling to the freezing point and gaining a deposit of frost.

Fig. 9.—Continuous records of the temperature 5 feet and 35 feet above ground on a tower in a pear orchard. Note the large difference in temperature at the two levels before the orchard heaters were lighted at 4 A.M. By 5 A.M. the temperature was practically the same at the two levels, showing that the heat from the burning oil had been nearly all expended in raising the temperature of the air within 35 feet of the ground. This point is further illustrated by the fact that at 5 A.M. when most of the heaters were extinguished, the temperature at the 5-foot level fell rapidly, while it remained practically stationary at the 35-foot level.—Weather Bureau.

In many orchards in the Rocky Mountain States, where fruit growing is highly profitable and the injury from frost more than probable every year, an extensive use is made of oil and other fuel-burning heaters between the rows of trees. Those who wish further information with regard to this matter should send to the Weather Bureau, Washington, D. C., for Farmers’ Bulletin No. 1096. At first thought it would seem that heat so applied would be blown away or instantly escape upward. But on frosty nights there is not much wind; if there is, there is little danger from frost. And then, as previously stated, on such nights there is what is called temperature inversion, and the temperature actually rises with the first few feet of ascent, and the heated air soon reaches air of its own temperature, when no further ascent occurs. When the air forty feet from the ground is ten degrees warmer than it is around and in contact with vegetation, as often occurs on frosty nights, the heat from the fires is nearly all expended in raising the temperature of the air within this forty feet. [Figure 9] furnishes the result of an experiment illustrating the correctness of the foregoing theory.

Fig. 10.—Average dates of last killing frost in spring.

Fig. 11.—Average dates of first killing frost in fall.

[Figures 10] and [11] show the average dates of the last killing frost in spring, and of the first killing frost in fall.

CHAPTER VIII
WIND AND PRESSURE OF THE GLOBE

CAUSE OF LOCAL WINDS AND OF GENERAL CIRCULATION

General Circulation. Differences in temperature, changing the specific gravity of the air, are the cause of the general circulation of the atmosphere about the earth, modified by the rotation of the earth; likewise the local circulation between land and water is caused by the different quantities of heat radiated by the two widely differing forms of matter, each attaining to a different temperature under the influence of the same solar radiation; and the inflow of winds to the cyclone and the outflow from the anti-cyclone are due to the same forces that cause the general and the local circulations.

If there were no difference in temperature between the equator and the poles the atmosphere would soon adjust itself in accordance with the laws of gravity, modified by the centrifugal force developed from the rotation of the earth, and the atmosphere forever would be at rest relative to the earth, moving with it as if it were a part of the solid sphere throughout its diurnal rotation on its axis and its annual movement about the sun. But there is a decided difference in temperature between the equator and the poles and between land and water surfaces; hence a general circulation, modified and distorted by numerous local movements, which, in turn, may be modified by the height of hills and mountains and the direction of their trend.

Fig. 12.—Trade wind circulation and reason for belts of high pressure at latitudes 30° N. and S. that extend around globe as shown by [Figure 13].

Let us trace a current of air through its course as shown in [Figure 12] and the reason for the blowing of the trade winds will be apparent, as will the reason for the location of a belt of high pressure at latitudes 30° north and south encircling the globe. At the equator there is a belt of calms. Here the air gently ascends under the intense heat of vertical sunshine. It is humid, for there is much water surface in the region of the equator, and the air carries vast quantities of water vapor aloft, later to be precipitated as torrential rains in the Tropical Zone, as the air cools by expansion in its ascent. This air expands or bulges upward and overflows aloft northward and southward, causing low air pressure at the equator, because of the quantity of air moved to other latitudes, which more than compensates for the amount banked up over the equator by the centrifugal force of the earth’s rotation.

Chart 1.—High and Low Centers of Action and Prevailing Winds of the Globe for July (Buchan).

Since air, passing away from the equator, must pass successively over parallels of latitude having less easterly velocity than that with which it started its journey, it runs ahead of the earth, and, relative to the surface of the earth, has a direction from the southwest north of the equator, and from the northwest south of the equator. Our current was divided at an altitude probably of six miles above the equator, one half following the northern and the other half the southern circuit. It was cooled by elevation and by radiation outward to space and as a result gained in weight and gradually descended, reaching the earth at about latitudes 30° north and south, and causing an accumulation of air at those latitudes and the belt of high pressure that irregularly surrounds the earth. In descending in the belt the air breaks up into a number of anti-cyclonic systems, sub-permanent highs or Centers of Action, which have so much to do with initiating the migratory Highs and Lows that create the weather of the earth, as will be fully explained in the [Chapter on Weather Forecasting]. The intensity of these centers of action is modified and their geographic positions shifted with change of season. (See [Charts 1] and [2.])

Chart 2.—High and Low Centers of Action and Prevailing Winds of the Globe for January (Buchan).

Trade Winds. But to return to the current that we left as it divided above the equator ([Figure 12]) and descended on an inclined plane to latitudes 30° north and south. It is cooler and dryer and heavier than when it started to ascend and it has lost the thousand miles per hour and more easterly velocity that it had at the equator and now only has the velocity that belongs to latitude 30°; therefore as it moves toward the equator from either side it lags behind latitudes whose easterly velocity is greater, and it takes up a direction partly toward the west, which, relative to the earth, makes it a northeast wind in the Northern Hemisphere and a southeast wind in the Southern Hemisphere. And thus is established a circulation the lower part of which is known as the “trade winds.” ([Figure 13].)

Navigators profit largely by availing themselves of the west winds in the middle latitudes and of the east winds in the tropics. To the daring and persistence of Columbus, and the force and constancy of the trade winds which blew him westward, we owe the discovery of America.

Fig. 13.—Average surface winds and pressure of the globe.

Winds of Middle Latitudes. Now study [Figure 12] and associate the information it conveys with that of [Figure 13], and observe that from the two belts of high pressure the air is pushed outward on both sides. In each case it starts as a true north or south wind, but, due to the rotation of the earth, is always and everywhere deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, and this deflection increases until what started as a poleward wind in the middle latitudes soon becomes almost a due west wind. In this region of west winds cyclonic storms are more frequent than in any other part of the globe. Now get clear in the mind the fact that no matter what may be the direction of the wind inside a cyclonic or anti-cyclonic whirl (often one thousand miles in diameter), the whirl is carried toward the east by the general drift from the west of the winds between latitudes 30° and 60°, and toward the west in the region of the trade winds.

Low Barometer at the Poles. Even though the air is contracted and rendered denser by the great cold of the Arctic regions, the pressure remains low because of the quantity of air driven equatorward by the centrifugal force both of the earth and of the winds themselves as they rim ahead of the earth and encircle the globe in the middle latitudes.

Data too Meager to Show Full Circulation Aloft of the Atmosphere of the Globe. Many charts have been published in the attempt to show how the atmosphere circulates below and aloft through the whole world. They only have speculative value, as our knowledge is too limited to permit us to unravel the complexities of all the upper movements.

Rain Winds of the Tropics. The trade winds, mostly moving over water surfaces, are laden with moisture, but, gaining temperature as they move towards the equator, their capacity to hold water vapor steadily increases, and therefore they do not become rain winds unless forced to ascend by the interposition of mountains, or until cooled by ascension at the equator. In no part of the world does the air rise so steadily and in such great volume as in the equatorial belt of calms and low pressure. Hence this is the region of greatest rainfall. During the two rainy seasons, spring and fall, the day opens clear; near midday the clouds gather and rain falls early in the afternoon; after which it quickly clears. This is so regular a program that one lays his plans accordingly. There is almost no rain in December and January; this is because the belt of calms and the inflowing trade winds move northward and southward with the migrations of the sun, and in December and January, the sun being far south, the northern trades, with their rainless winds, cover the equator and the region formerly occupied by the belt of calms. In midsummer the sun is far north and then the southern trades move up and give dryness to the equator. In the northern trades, of the moderate amount of rain that falls, the greater quantity falls in summer; in the southern trades the order is reversed.

Rain of the High-Pressure Belts and of the Regions of West Winds. In the high-pressure belts the air is settling down and gaining heat by compression and there is not much horizontal movement. These are, therefore, regions of but little rainfall, and all the great deserts occur in or near them. The belts of west winds are the regions of most frequent cyclonic activities. Here the rainfall is quite equally distributed throughout the year and is the result of the mixing of the air by storms and its cooling by expansion as it is carried upward in the migrating whirl.

Circulation between Continents and Oceans. In [Chapter X], under the sub-caption “Influence of Continents and Oceans on Climate”, the circulation between them is well explained. In general the movement is from the continent to the oceans in winter, with the air flowing inward aloft to settle down and take the place of that which passes out to sea. In summer the directions are reversed.

Daily Variation in Coastal Winds. In summer, when there are no forceful storm winds blowing steadily from one direction for several hours at a time, there will daily spring up gentle to fresh winds from the surface of oceans and large lakes to the land, because of the influence of the sun’s rays in heating the land to a higher temperature than it does the water. These winds will not appear on cloudy days and they will extend inland but a few miles.

Monsoon Winds. During winter the vast continent of Eurasia (Europe and Asia) cools to such an extremely low temperature as to develop a High, or center of action, of great energy and extent, which drives a steady dry monsoon into the Indian Ocean and China Sea. Unlike the trade winds, these winds reverse their direction in the summer; then the intense heat of the continent to the north develops an extensive Low, which draws the ocean winds inland and extends its influence so far south as to attract the southeast trade winds of the Southern Hemisphere and, turning them so that they flow from the southwest, continue them far into the interior of Asia. Since the summer monsoon blows from a tropical sea it comes heavily laden with water vapor and as it rises over the mountains of the great Himalayan system copious rains are precipitated. In Australia, Africa, South America, and some parts of the North American continent monsoon influence in various degrees is felt, but in no place is the monsoon so important as in the countries bordering the Indian Ocean. ([Charts 15] and [16].)

Föhn Winds. This is a hot wind that sometimes blows down a mountain side in the Alps. In the Rocky Mountains it is called the Chinook Wind. It is caused by moisture-laden air being drawn over a high mountain so quickly that the heat liberated in condensation does not have time to escape by radiation. The air cools by expansion as it ascends on the west side of the mountain, but it gains this all back by compression as it descends, and it has added to its temperature much of the heat of condensation. It is dry and greedily evaporates snow from the ground in winter, clearing off a deep covering within a few hours.

Fig. 14.—How winds would blow into a cyclone on a non-rotating earth.

How Winds Are Deflected by Earth’s Rotation. Every free-moving thing, whether wind or projectile, is deflected to the right of its initial direction by the rotation of the earth in the Northern Hemisphere and to the left in the Southern Hemisphere, unless the object be moving exactly along the line of the equator. Winds moving inward to a Low are therefore so deflected as to cause the cyclone to gyrate in a direction contrary to the movements of the hands of a watch. In an anti-cyclone the movement is with the watch. In the Southern Hemisphere these wind directions are reversed.

[Figure 14] gives an illustration of what would be the movement of air inward to a cyclone on a non-rotating earth. The winds would blow along radial lines for a time, but, converging together as they began to ascend, they doubtless would soon set up a gyration about the center. On a non-rotating earth this gyration would be clockwise as often as it would be anti-clockwise, but on a rotating earth the gyration can be in but one direction. ([Figure 15].) Even tornadoes, whose diameters of rotation are never but a few hundred feet, obey this law. In little dust whirls, in which the movements of air may be comprehended from the motion of the trash that is whirled about and which are tornadoes in miniature, the direction of gyration may be either way. They are too small for the deflecting force to be appreciable, and it may be that the tornado is forced to take its direction of gyration from the cyclone in whose southeast quarter it has its origin.