What Makes The Weather

( Originally Published Early 1900's )

JUST as music has often been termed the universal language, so may the weather well be called the universal subject of conversation. How we do like to talk about the weather ! "It's a great day today!" "Isn't this a dandy?" These and a hundred other equally conventional salutations are given utterance by rich and poor alike, by bank president and office boy, by farm-owner and farm-hand in short, by everybody, for, happily, no one person nor group of persons as yet possesses a monopoly upon the weather. While some may speak about the weather a bit more intelligently than others, the subject is one that may be frankly discussed at any time any-where. Who can point out another topic which is always appropriate upon any occasion?

At the first suggestion of a balmy day after a long winter spell we steal out into the garden, turn up a rotted board here, push back some wet leaves there, grub with a stray weathered stick, hoping to catch some glimpse of our faithful tulips poking their bleached noses through the mulch, or the curled fronds of the dainty fern attempting to uncoil into spring's daylight. Friend neighbor spies us and, plucking up courage to venture into his garden, greets us across the hedge fence with an enthusiastic "Anything coming up? Fine weather to-day!"

It is well that our common basis for friendly exchanges should focus upon the fascinating subject of the weather. But still more worth while is the acquisition of some knowledge about the variable state of the atmosphere, to the end that we may make some good use of it. The ancients inquired into the daily weather changes, but the best they could do was to correlate them with the elements of their environment, such as the moon, the sky colors, the sun, the behavior of plant and animal life, and even the variations in their own bodily feelings. We have made progress since those days, yet millions of people still use the signs pictured in the almanac or the traditional ancestral beliefs to guide them in planting their gardens, or to forecast the weather for some other occasion. A few of the guides may be substantiated upon scientific grounds, but most of them contain no truth whatever. We shall give more detailed consideration to these aspects of the weather in a chapter on Weather Lore. However, the realities of our atmosphere deserve attention first.

Persons living in the eastern two thirds of the United States have long been familiar with the tremendous variability of the atmosphere. Shifts in temperature amounting to 40 degrees in twenty-four hours or less are not infrequent; rapid changes in the moisture content of the air from an extreme humidity which borders upon fog conditions to a sunny dry atmosphere that bakes the soil surface are no strangers in these parts. Even in the far West, where the desert dominates the landscape, frigid nights often mark the end of fiery hot days, while clouds of dust particles obliterate in a few moments a vast expanse of crystal-clear blue skies. This variability seems to make for progress. At least, the most progressive peoples of the earth inhabit the regions where these kaleidoscopic changes occur most frequently.

The responsibility for the fluctuations in our enveloping atmosphere rests primarily with the sun. Every one recognizes the presence of the sun in the heavens and not only looks to it as a source of heat but appreciates its contribution toward making us feel cheerful upon "sunny" days. However, both the warming and lighting effect of the sun are dependent in large part upon the atmosphere.

The heat received from the sun by the earth is known technically as insolation. It is not measured in terms of degrees as we measure the temperature of the air but in terms of its heating capacity. As the heat from the sun passes through the air, only a small amount, probably less than a third, is absorbed by the air, while the balance reaching the earth's surface itself is absorbed in part and in part reflected back into space. The lower atmosphere, or that part in contact with and close to the land and water bodies, is heated by conduction from the earth, by radiation from these surfaces, and by convection.

Nearly six sevenths of the earth's suface is water and the rest land. If the earth were all water, the variability in atmospheric conditions would be materially reduced and simplified. Like-wise, if it were all land, uniform in color, in density, and in height, the present diversity in atmospheric conditions would be replaced by a relatively simple situation. But since neither condition exists, but on the contrary both water and land are irregularly distributed, uneven in surfaces and different in color, their effect upon the state of the atmosphere is exceedingly complex.

As a further influence upon our atmosphere we must recognize the rotation of the earth once in twenty-four hours, which causes the succession of daylight and darkness and a consequent fluctuation in the amount of heat absorbed and radiated ; again, the earth revolves about the sun once in a year, moving in an elliptical path and varying in its distance from the sun during this time nearly 3,000,000 miles. But this is not all, for the earth's axis is inclined at an angle of 231/2° from a vertical, resulting in the sun's rays having to penetrate different thicknesses of air at different points on the earth's surface in the course of a year. The combined effect of the inclination of the axis and of the revolution produces our seasons, and these by no means are everywhere alike.

As we go our regular rounds, transacting the affairs of the day and returning home at dusk to enjoy our evening's rest, visit a theater, or indulge in some other form of recreation, we are inclined to take for granted that what happens by way of shifts from daylight to darkness and back to daylight is after all a simple matter and not for our particular concern. As the days shorten and the nights lengthen, as the seasons follow one another from warm to cold or perhaps dry to wet and back again, we take note, for we must make adjustments in the matter of clothing, or crop production, or heating of the home, or in a hundred and one other ways. But as creatures of habit we accomplish these ends almost automatically and rarely pause to inquire into the cause of all this. Mark Twain once said that everybody talks about the weather but no one seems to do anything about it. While we should not take this great humorist too seriously, yet it is worth observing that, although in his day relatively little was known about the causes of our weather, much knowledge has been added since. To be sure, in a sense there is little that we can do about these earthly variations, for man's dominance over the weather and climate is still but infinitesimal. Nevertheless, our existence is so vitally affected by the relation of the sun to the earth and the earth to the sun that our understanding of their interactions and in turn of our reactions must, it seems, prove highly profitable. The Smithsonian Institution and the National Geographic Society recently have de-voted part of their energies to a scientific investigation of the influence of the sun's radiations upon our weather. Should certain of the present theories be borne out and a mathematical relationship be established, the consequences may be far-reaching, particularly in the field of fore-casting. We may find it possible ultimately to predict our weather weeks and even months in advance.

Until recently man has been a creature of the bottom of the atmosphere. He has, on occasion, in a captive balloon, free air balloon, or airplane ventured an attempt to penetrate the atmosphere to considerable heights, and with the latter heavier-than-air machine he has learned how to move rapidly through the air, rising or descending at will. Yet withal, he still is confined to the lower air layers, the maximum altitude thus far attained being 42,470 feet. In fact, if the distances are drawn to scale and compared with the total thickness of the atmosphere, his maximum rise even with the aid of tanks of oxygen represents almost no rise at all.

Within the lifetime of the present older generation there was a period when it was supposed that the air was six or seven miles thick. This was increased later to ten or twenty miles, and now we figure it far beyond these estimates. That strikingly beautiful and little understood phenomenon, the aurora, indicates that the atmosphere extends to a height of from 300 to 400 miles. The late geologist Dr. Chamberlin of the University of Chicago, with the aid of the astronomer Dr. Moulton, until recently in the same institution, calculated that the earth is capable of holding an atmosphere as far away as 600,000 miles. Certainly at this distance the air would be so rare as to approach a vacuum. Such distances we cannot really comprehend. We are, indeed, little animals confined to the bottom of the vast sea of air, just as some varieties of fish spend their lives in the depths of the sea of water. An occasional pause during our busy lives to consider some of these relationships may lead us to show a higher regard toward Mother Earth than we now reveal.

As interesting as is speculation concerning the height of the atmosphere, a knowledge of its composition and the functions of its parts will assist us in a clearer understanding of some of the weather effects about which we often wonder. Needless to say, the atmosphere is a very complex affair made up of oxygen, nitrogen, carbon dioxide, water vapor, ozone, neon, xenon, argon, crypton, helium, and still other gases, as well as myriads of dust particles. Although all of these gases have importance, certain of them seem to have a greater significance for man than others. Three of them compose the major part of the atmosphere, namely, nitrogen 78 percent, oxygen 21 percent, and carbon dioxide three hundredths of one per cent. Since the remaining percentage includes all the other gases, it is plain that each one can occur only in minute quantities. These figures represent the proportions for dry air. But air usually is mixed with some water vapor. When this is the case, then the water vapor actually replaces the other gases. Its percentage of the air may range from nothing to as high as 4 or 5 per cent by volume.

The term oxygen is fairly well known to most persons, because we have been taught, from early childhood almost, that without this gas animal life could not exist. Also, without oxygen the burning of materials, that is, the oxidation process, could not happen. The medical profession at times uses this gas in concentrated form for per-sons critically ill for whom oxygen, as it-.occurs in the normal atmosphere, is insufficient.

Carbon dioxide bears a relation to plant life similar to that which oxygen bears to animal forms. For man this gas is of significance because of its heat-retentive qualities. While fairly constant in quantity in the air at any given time, it seems to vary in the course of eons of time, if not in so short a period as a few thousand years. Estimates have been made which indicate that if the present amount of carbon dioxide were doubled, that is only .03 of one per cent added, the temperature of the atmosphere would be unbearable for man. In contrast, if the amount were halved, the air would become so cold we could not survive.

Nitrogen has probably received more attention from the general public since 1914 than at any previous time. Before the World War we recognized the value of nitrogen as a fertilizer, and as a gas taken from the air by the bacteria on plant roots. Many plants serve as fertilizing crops. Alfalfa and clover are among the best-known types of vegetation which often are planted primarily for the nitrogen contribution which they make to the soil. Nitrate salts, practically all of which have come from the desert lands of Chile, have been imported for many years by most modern countries. They have been used not only for fertilizing crop :lands but for industrial purposes, especially the manufacture of explosives. The war required of some countries, particularly Germany, which was cut off from a supply of Chilean nitrates, that nitrates be produced from some new source if the war were to be continued. This resource was essential both for crops and munitions. In consequence, great progress was made in the extraction of nitrogen from the air. This had been done before, but neither upon a large scale nor upon a commercially successful basis. In the years during and since the war, processes for the extraction of nitrogen from the air in the form of nitrates have so improved that to-day the industry in Chile, where the product has so long been shoveled from the earth, is seriously threatened. This means the entire nation of Chile is disturbed, be-cause its welfare is largely dependent upon the sale of nitrates.

The water vapor of the atmosphere, in many respects one of its most interesting elements, we shall discuss in some detail in Chapter II. As it occurs in the air it is an invisible gas, yet with relatively slight temperature changes it becomes visible and we recognize it with the naked eye as cloud, fog, rain, snow, or other forms. Like carbon dioxide, it too affects the amount of heat which the atmosphere holds, but in this respect plays a less significant part. However, as a source of water for all life, its importance cannot be overemphasized.

Many persons complain about the dust. We don't like to have dust particles lodge in our eyes, or accumulate upon furniture or other articles in our homes and offices, or gather upon our clothes. Yet dust is as essential to our well-being as the other elements of the atmosphere. Without dust atmospheric precipitation would be greatly reduced, as it is upon the dust particles that much of the water vapor condenses to form rain, or snow, or other moisture element. Without dust we would experience an odd distribution of light, so strange that our progress no doubt would be greatly interrupted. Dust particles, and to some degree water vapor, scatter sunlight by reflection. If there were no dust, places not receiving the sun's rays direct would be in darkness. Light rays do not bend around corners ; dust particles take them around through reflection. Again, like carbon dioxide and water vapor, dust serves slightly in controlling the temperatures of the atmosphere.

All of these gases together weigh something. This we know from personal experience. When the wind blows that is, when the air in motion presses against us so hard that we find walking difficult or the retention of a hat on our heads impossible we know air has weight. When paper, or dust, or clouds, or balloons float in the air we know air must have weight. It is the weight of the air which supports the airplane. However, to know from these general observations that it has weight is well enough for ordinary purposes, but to be able to measure its weight exactly is of still greater importance. The weight of the air is known as its pressure, and one of the most influential factors in our changing weather is the variation in atmospheric pressure.

Air is weighed by means of a device called a barometer. The standard instrument consists of a glass tube about thirty-six inches long, a quarter inch in diameter, sealed at one end, filled with mercury, and the open end immersed in a small well of mercury. Before the mercury is placed in the tube all the air is exhausted. The height of the column of mercury in the tube, after the immersion of the lower end, just balances the down-ward pressure of the air upon the mercury in the well, the surface of the latter being exposed to the air. The weight of the column of mercury must equal the weight of the air supporting it or, conversely, the air supporting the mercury weighs as much as the mercury. Under normal conditions at sea-level, the column of mercury is nearly thirty inches long and weighs just 14.7 pounds or roundly fifteen pounds to the square inch.

Instead of referring to weight of air when we desire to indicate its pressure, we just refer to the height of the column of mercury. Fluctuations in air pressure may be frequent and sudden, but the range lies between the extremes of twenty-six inches and thirty-two inches. Neither of these is reached normally. The ordinary range may be approximately from 29.0 to 30.5 inches at sea-level, or its equivalent. These variations in atmospheric weight or pressure constitute the basis for scientific weather forecasting which we shall consider later.

Because the mercurial barometer is rather cumbersome, a more simple though less accurate instrument has been devised the aneroid barometer. Aneroid means without air and has reference to a series of one to six or more hollow disks from which nearly all the air has been pumped. In order to prevent the walls from caving in, a spring device has been placed within each disk to support it. When the pressure of the atmosphere is high the walls of these disks are slightly compressed, and when the pressure falls they are released. These movements are, carried to a hand attached to the series and this in turn moves over a dial upon which a pressure scale is printed. The scale is adjusted by the manufacturer of the instrument by comparing the motion of the hand with the rise or fall of the mercurial barometer. Although not as reliable as the latter, yet for all ordinary purposes it answers very well. These instruments are made in attractive designs and prove not only useful as aids to weather forecasting but desirable additions to the home furnishings.

If we could see a cross-section of the atmosphere from top to bottom we would observe the greatest density in the lower portions and a rapid decrease toward the upper layers. The rate of decrease is by no means uniform. Most of the air lies within the first four miles of the earth, while the balance is distributed throughout those thousands of miles mentioned in the earlier part of this discussion. We have very slight knowledge of the air at heights above four to six miles, but information is being steadily accumulated through small pilot-balloon observations, studies of shooting-stars, meteorites ( fragments of shooting-stars which reach the earth), auroras, and more recently the behavior of wireless or radio waves.

What effect the upper atmosphere, called the stratosphere, has upon our weather is still a mat-ter of conjecture, but students of these areas are of the belief that a close relationship exists. Nature is so well ordered, and all of her activities seem to be so thoroughly coördinated, it is hardly conceivable that the vast variability in atmospheric conditions close to the earth's surface and affecting our weather are not intimately associated with the rest of the atmosphere, even to its outer limits.

From the foregoing statements we can appreciate the many elements that play a part in our weather. There may be others with which we are not yet acquainted. Scientific men, students of the physics of the air or of meteorology, as the scientific study of the atmosphere is termed, realize that they have much to learn about the behavior of these gases which surround us. They know many of their characteristics and a few of the factors which "make" our weather, but they expect to have to search many years more for additional facts before they will fully understand all the peculiarities of our weather.