The Mentor: The Weather Part 1

The Mentor: The Weather.

by Charles Fitzhugh Talman.

Old Probabilities

Shall tomorrow's weather be fair or foul? Blow wind--blow moistly from the South, for I go afis.h.i.+ng. "Nay, good friend," exclaims the golfer, "the day must be dry and the wind in the west." The farmer moistens his finger and points it toward the sky. "Rain, come, quickly, for my crops," is his prayer. But the maiden's voice is full of pleading: "Let the sun s.h.i.+ne tomorrow that my heart may be light on my wedding day."

And so, through the days and seasons, humanity with all its varied needs, turns anxiously, entreatingly to Old Probabilities. And how is it possible for him to satisfy the conflicting demand? He may, on the same day, please the farmer in the West, the fisherman in the South, the golfer in the northern hills, and the bride in the eastern town. But how can he suit them all in one locality on a single day? Old Probabilities is willing and he loves humanity, but his powers and privileges are limited. There are those who say that it is due to the kind endeavors of Old Probabilities to satisfy everybody that our weather has at times become so strangely mixed.

Old Probabilities is a gentle family name and came out of the affection of the people. The name was a matter of pleasantry. It was given to the Chief of the United States Weather Bureau when the department was first established by Congress, and its source lay in the phrase, "It is probable," with which all the weather predictions began. But Old Probabilities, genial prophet and lover of his fellow men, is pa.s.sing away, for the officer who organized the Weather Bureau became in time displeased with the name and changed the form of the daily prediction so as to read, "The indications are." The phrase is formal and severe.

There is naught but cold comfort in it. Our hearts turn back fondly to Old Probabilities and his friendly a.s.surance: "It is _probable_ that tomorrow will be fair."

[Ill.u.s.tration: Chickamauga Park, Tenn., in an Ice Storm]

THE WEATHER

By CHARLES FITZHUGH TALMAN

_Librarian of the U. S. Weather Bureau_

THE MENTOR DEPARTMENT OF SCIENCE JULY 1, 1916

_MENTOR GRAVURES_

CENTRAL OFFICE OF THE U. S. WEATHER BUREAU, WAs.h.i.+NGTON, D. C.

A SIMPLE WEATHER STATION A MAJESTIC c.u.mULUS CLOUD THE OBSERVATORY ON MONTE ROSA LAUNCHING A METEOROLOGICAL KITE THE EFFECTS OF SNOW AND ICE--THE CAMPUS, PRINCETON UNIVERSITY

[Entered as second-cla.s.s matter, March 10, 1913, at the postoffice at New York, N. Y., under the act of March 3, 1879. Copyright, 1916, by The Mentor a.s.sociation, Inc.]

It is easy to lay too much stress upon the unimportant aspects of weather. It furnishes a bit of conversation over the teacups; it accentuates the twinges of rheumatism; it spoils a holiday. All this, however, is mere byplay.

The real work of the weather--the work that explains the existence of costly weather bureaus, such as the one upon which our Government spends more than a million and a half dollars annually--is momentous beyond calculation. Consider such facts and figures as these:

The head of the British Meteorological Office recently declared that bad weather costs the farmers of the British Isles about one hundred million dollars a year. In our own country it has been estimated that a difference of one inch in the rainfall occurring during July in six States means a difference of two hundred and fifty million dollars in the value of the corn (maize) crop. The world over, the damage wrought by hail-storms is said to average about two hundred million dollars a year. In the city of Galveston a single hurricane once destroyed twenty million dollars' worth of property and six thousand human lives. Thus we might proceed indefinitely.

The fact is that man's welfare is conditioned to an enormous extent and in an endless variety of ways by the vicissitudes of the atmosphere; hence the study of weather--meteorology--is one of the most important of sciences. It is also one of the most strikingly neglected!

At the office of the Weather Bureau in Was.h.i.+ngton there is a meteorological library of some thirty-five thousand volumes. But meteorological libraries are rare; meteorological books are scarce in other libraries; and meteorologists are so uncommon that whoever declares himself one is likely to be asked, "What _is_ a meteorologist?"

[Ill.u.s.tration: STATIONS OF THE UNITED STATES WEATHER BUREAU

Showing two extreme types: one, an office on the twenty-ninth floor of the Whitehall Building, New York City, with instruments installed on the roof; the other, an independent observatory building, with free exposure on all sides, at St. Joseph, Mo.]

The "meteors" studied by the meteorologist are not shooting stars, but the phenomena of the atmosphere,--rain and snow, cloud and fog, wind and suns.h.i.+ne, and whatever else enters into the composition of weather and climate.

THE ATMOSPHERE

The ocean of air in which human beings live, even as deep-sea fishes live at the bottom of the liquid ocean, is called the _atmosphere_.

Unlike the liquid ocean, it diminishes rapidly in density from the bottom upward. At an alt.i.tude of three and one-half miles it is only half as dense as at sea-level. This is higher than the highest permanent habitations of man. Mountain-climbers and balloonists have attained greater alt.i.tudes; but above a level of about five miles the air is too greatly rarefied to support life. Balloonists who ascend still higher must carry a supply of oxygen with them. A little above the ten-mile level the air is only one-eighth as dense as at sea-level. The atmosphere extends at least 300 miles above the earth, at which height its density is computed to be only one two-millionth as great as at sea-level.

The weather with which human beings are concerned may be said to extend upward seven or eight miles; _i.e._, to the level of the higher clouds.

The layer of the atmosphere lying between sea-level and the upper cloud level has certain characteristics that distinguish it from the air above it, and is known as the _troposphere_.

The heating of the atmosphere by the sun is the beginning of all weather, and the temperature of the air is the most important weather element. As soon as we begin to study atmospheric temperature, we encounter a paradox. The heat of the air is all derived from the sun (except a minute quant.i.ty from the interior of the earth, and an infinitesimal quant.i.ty from other heavenly bodies), and it would therefore seem at first glance that the upper layers of the atmosphere should be warmer than the lower. Experience proves the reverse to be the case. A mountain overgrown with tropical vegetation on its lower slopes is, if high enough, crowned with eternal snows. A thermometer carried upward in the air shows under average conditions a fall of temperature of one degree (Fahrenheit) for every 300 feet of ascent. This fall of temperature with ascent continues to the upper limit of the troposphere, where the average temperature is something like 70 degrees below zero.

[Ill.u.s.tration: THE NEW IDEA IN WEATHER OBSERVATORIES

The Observatory of the Ebro (Spain), founded by Spanish Jesuits, is devoted to studying the interrelations of sun, earth and air. Its admirable equipment includes apparatus for the direct and spectroscopic study of the sun, for measuring solar radiation, atmospheric electricity, earth currents, terrestrial magnetism, and earthquakes; besides the ordinary routine of a meteorological observatory. The results of all these observations are published side by side, to facilitate comparison.]

Above the troposphere is a region called the _stratosphere_, or _isothermal layer_, in which an ascending thermometer shows irregular and generally small changes of temperature--not infrequently a rise of temperature with ascent. The exploration of the stratosphere is one of the most fascinating fields of meteorological research, but lies somewhat beyond the scope of an essay on weather. It is carried out chiefly with the aid of small free balloons, some of which (sounding balloons) bear self-registering thermometers and other instruments, while others (pilot balloons) bear no instruments, but show by their movements the drift of the air currents. The greatest alt.i.tude ever attained by a sounding-balloon was 21.8 miles; by a pilot-balloon, 24.2 miles. The branch of meteorology dealing with the study of the upper air is called _aerology_.

[Ill.u.s.tration: A LONELY OUTPOST ON THE VERGE OF THE ANTARCTIC

The Argentine meteorological station in the South Orkneys. Once a year an expedition is sent from Buenos Aires to relieve the staff of four observers. This is the southernmost permanently inhabited spot on the globe; and it has not even wireless communication with the rest of the world.]

Reverting to the temperature of man's environment, the reason why the atmosphere is warmest at the bottom is this: The sun's rays come to us from outer s.p.a.ce in the form of vibrations in the ether, and warm the air to only a slight extent in pa.s.sing through it. They are absorbed by the ground, and converted into heat waves. The air is then warmed by contact with the warm ground. Lastly, the warming of the lower air gives rise to air-currents, which distribute the heat through the atmosphere.

BAROMETRIC PRESSURE

If our weather were uniform, it would furnish little matter for conversation; in fact, would hardly be weather at all. Changeableness is the salient feature of weather, and to understand weather changes one must know something about barometric pressure.

Like all other forms of matter, the invisible air has weight. At sea-level it exerts a downward pressure averaging 14.7 pounds to the square inch. Atmospheric pressure is measured by means of an instrument called the _barometer_, in which the weight of the air is balanced against a column of mercury. As the height of the mercurial column varies with the pressure of the air, and is taken as the measure of the latter, we follow the practice of expressing pressure (a force) in linear units (inches or millimeters). This practice is retained even in the use of the aneroid barometer, which contains no mercurial column.

Hence, when we say that the average barometric pressure at sea-level is 29.92 "inches," we are really expressing in a roundabout way the weight of the air at that level.

[Ill.u.s.tration: HOW THE CAMERA a.n.a.lYZES LIGHTNING

The same flashes photographed with (_a_) a stationary camera, and (_b_) a camera revolving on a vertical axis. One of the flashes is seen to have consisted of several successive discharges along an identical path

Courtesy of U. S. Bureau of Standards and Popular Science Monthly.]

Barometric pressure not only varies somewhat regularly with alt.i.tude--diminis.h.i.+ng as we ascend--but also less regularly from place to place in a horizontal direction, and from time to time at a given place. In studying the weather meteorologists frequently wish to compare the barometric pressures prevailing at a certain time at a number of places lying in the same horizontal plane. Given a system of meteorological stations scattered over a certain territory, the first step is to secure simultaneous readings of the barometers at these stations. Then, if the stations are at various alt.i.tudes, as they commonly are, corrections must be applied to the readings to reduce all to a common plane; the plane adopted for this purpose is sea-level.

Since most stations are _above_ sea-level, and since atmospheric pressure diminishes with alt.i.tude, reduction to sea-level generally involves applying an _additive_ correction.

THE WEATHER MAP