Popular Science Monthly/Volume 23/October 1883/Cyclones and Tornadoes
|CYCLONES AND TORNADOES.|
By GEORGE CLINTON SMITH.
TOWARD the western portion of the United States, along the twenty-fifth parallel of longitude, lies a vast tract of sandy, arid country, known to the earlier geographers as "The Great American Desert." It is true, the limits of this great area have become circumscribed by the onward march of civilization, but the sandy waste is still there, and must ever remain. Still farther westward, the Rocky Mountains rear their lofty, snow-crowned heads in one continuous chain, three thousand miles in length. Rich in mineral wealth, the delight of tourists, and the home of a prosperous people, these mountains have a different and equally valuable office to perform in the exercise of an important influence upon the climate of our continent. Were they to be removed, the entire territory west of the Mississippi River would soon become an arid, lifeless desert.
All storms, of any magnitude, that visit the United States, except the tropical hurricanes which sometimes touch the southern coasts, have a common origin in or near the Rocky Mountains. Here the first barometric depression is felt, preceded by a rising temperature, caused by the warm winds moving northward over the sun-heated sands of Arizona, New Mexico, and Western Texas. These warm, rarefied currents of air are met by cooler currents passing over the snow-clad peaks of the north; a cyclonic storm is formed, usually small at first, which begins its journey eastward, gradually developing in energy and area as it goes. After leaving the mountain-ranges, there is but little precipitation for the first few hundred miles; as it advances, it usually widens from north to south, but the line of travel of the storm-center can be readily predicted by the Signal-Service observers, and its location at any time fixed by the lowest reported reading of the barometer.
During the journey of the storm eastward or southeastward, the wind in advance of it will be easterly, blowing off an area of high barometer into the low; and the barometer will continue to fall. Toward the north of the storm, the wind will be north; and to the south of it the wind will blow from the south, frequently causing what are known on the Western plains as "sand-storms"; while, if the storm occurs during the winter season, the wind and snow in the northern portion is called a "blizzard." In the rear of the storm the wind will be westerly, shifting to northwest, frequently blowing a gale; the barometer will rise and the temperature will fall, sometimes rapidly, and clearing weather will follow.
Thus it will be observed that the true axis is the "storm-center," and that the storm revolves on this axis as it moves forward in an easterly, northeasterly, or southeasterly direction. This is the true cyclone. It may be only a few hundred miles in diameter, or its influence may be felt from British America to the Gulf of Mexico. It may be accompanied by what are known as local showers or storms; or the rains may be general, and of several days' duration. The greatest precipitation is frequently in advance of the storm-center, and may be either rain or snow, depending upon the season of the year and the temperature. During the spring and summer months the area of low pressure is usually accompanied by precipitation in the form of local showers, or thunder-storms, of more or less severity, in which case the strongest air-currents move with the local storm-cloud, and are known as simply high winds, sometimes approaching the severity of a hurricane, but seldom extending over any considerable area of territory.
The true cyclone usually travels from the Rocky Mountains to the Atlantic coast, in nearly a straight line. Sometimes the distance is traversed in four days and nights, exceeding the speed of a railway express-train; but frequently the progress is slow, and the time required much longer, depending largely upon the atmospheric conditions met with in the vicinity of the Great Lakes.
Frequently, while the wind may be blowing from the southeast or northeast, or between these points, the storm is approaching from an opposite direction, and pushes out its cloudy streamers, or "feelers," hundreds of miles in advance. There is, then, no such thing as a "northeast storm," as far as the interior of this continent is concerned.
The origin and movement of continental cyclones being understood, we naturally turn, next, to the investigation of tornadoes. These seem to occur most frequently in the Western States, and are usually confined to the territory between latitude 35° and 45° north, and longitude 10° and 25° west. They are purely local in effect, although their cause may be remote; always depend upon and frequently accompany the meteorological conditions developed during the progress of the cyclone proper across the country. They may occur near, or in advance of, the cyclonic storm-center; or they may appear near the outer edge of the general disturbance, hundreds of miles away. They usually develop within the area of highest temperature, and are often preceded by a brassy sky, and hot, gusty winds, sometimes followed by a sultry atmosphere and an ominous calm. They occur most frequently near the close of the day, their general direction being from southwest to northeast. They vary much in size and force, but all have the same general characteristics in regard to appearance and action; being a funnel-shaped cloud, heavily charged with electricity, that goes bounding and whirling along in close proximity to the earth's surface, dealing death and destruction wherever it touches. The generally accepted belief is, that tornado-clouds are formed suddenly, by the meeting of warm and cold currents of air; or, by the union of a positive with a negative cloud, a partial vacuum being formed, constitutes the axis around which the cloud begins to whirl, gathering strength and increased velocity as it goes.
As the tornado now sweeps onward in its course, it rises and falls with a series of bounds, and, with a swaying motion, describes a zigzag course, now forming a chain of loops, and again shooting off on an obtuse angle, varying in the speed of its forward motion, which may be anywhere from ten to thirty miles an hour. At the same time it is rapidly whirling on its axis in the opposite direction from a screw, or the hands of a clock, the air revolving around the vortex necessarily attaining a speed of several hundred miles an hour. First widening, then contracting, now bounding above the tree-tops, and again descending to sweep the earth bare of every object within its reach, the aerial monster surges onward. The largest forest-trees, mere playthings in its grasp, are plucked up by the roots, or snapped off like pipe-stems; substantial buildings are first crushed like egg-shells, then caught up in the vortex and the débris carried sometimes for miles, before it is again thrown off by centrifugal force, and falls by gravitation anywhere, everywhere, as soon as released from the monster's grasp.
It is difficult accurately to describe the tornado's appearance and work, even for those who have been eye-witnesses, or who have personally passed through the horrors its coming brings. While accounts differ as to its appearance and behavior, as witnessed from different points of observation and under different circumstances, all substantially agree that it is cone-shaped, its motion rotary, that its apex resembles fire and smoke, and that vivid lightning and heavy rain-fall usually accompany it. In rare instances, electricity, in the form of St. Elmo's fire, will precede the vortex, and a white, steamy cloud will follow. It will be observed that the form of the tornado-cloud is nicely illustrated by the "proof-plane" used in teaching natural philosophy. The small end of the plane is most heavily charged with electricity, and, the nearer it approaches to a perfect point, the greater will be the accumulation: a high tension is caused, and the electricity must escape by some conductor. So, in the tornado-cloud, the smaller the point or stem, the greater the force exerted when it meets the earth.
The bounding or swaying motion of the tornado can be illustrated by the experiment of the "electrical puppets": the cloud above forming the upper plate, and the earth beneath the lower one. All light objects between are drawn up, then thrown down—being first attracted, then repelled.
While the tornado, on its course, possesses four distinct motions—as previously stated there seems little doubt that the central force, or the one exerting the greatest power, is purely electrical, although the outer surface of the vortex be composed of wind moving at a rate of speed that can scarcely be comprehended.
So many readers are already familiar with statements frequently made regarding the tornado's strange freaks, that a few illustrations only will be given.
Mr. C—— states that, during the tornado which visited Sangamon County, Illinois, on May 18th of the present year, while himself and family had taken refuge in the cellar, a sulphurous smell prevailed, a ball of fire burst above them, and they were severely burned about the face and neck, but otherwise uninjured, although the house was torn from over then-heads.
The family of Mr. T——, who had also sought shelter in a cellar from the same storm, were covered with a gummy substance, which would not wash off! This substance might have been formed from the sap of trees and juice of leaves, combined with the moist, heated atmosphere. In passing over the track of the tornado, the writer observed two large elm-trees torn out by the roots; one had fallen to the east, the other to the west, and the tops of both were firmly interlocked. A short distance from these, a white-oak tree, thirty inches in diameter, was broken off and lay upon the ground, the top toward the west; on top of this lay another large tree, which had stood in a northwest direction from the first. The rotary motion of the destructive force was here clearly proved. A thrifty young maple-tree, twelve inches in diameter, stood apart from other trees, near the edge of the storm's track. About six feet from the ground the bark was peeled entirely off for a distance of two feet. No broken limb, or other missile, lay near the tree, and its top was uninjured! Could this effect be produced by wind? Was it not, more likely, caused by concussion?
In the same tornado a whole orchard was swept away; the large trees carried one fourth of a mile, stripped of their bark and smaller limbs, and completely plastered with mud. A wagon-tire was torn from the wheel, straightened out, and driven into the side of a building. A flock of geese were plucked of their feathers, which were deposited in a hedge-fence, giving it a complete coating.
Credible persons testify to having seen a horse carried over the roof of a barn, and again let down, without receiving serious injury. A child's necklace, with locket attached, was picked up in the village of A——, having been carried by the storm from W——, eight miles distant! Mr. and Mrs. T——, living in L——, were both killed, and their house destroyed by the tornado. A vest belonging to Mr. T——, containing valuable papers and a sum of money, was found in the town of P——, twenty miles away, and restored to the relatives of the deceased owner!
Wagons, agricultural implements, and household furniture, will be carried a long distance and broken into fragments by the tornado, while delicate mirrors and sets of glass-ware may be spared. The giants of the forest will be torn to splinters, while the modest flowers beneath them are left blooming as sweetly as if nothing had occurred!
The belief has obtained to some extent that tornadoes follow subterranean veins of water. That they are repeated in certain localities, have a fondness for belts of timber and small water-courses provided they run in the right direction there can be no doubt. They also travel over a portion of country previously moistened by rain. This rule has but few exceptions.
The increasing frequency and severity of these visitations (notwithstanding what may be said to the contrary) compel the writer to believe that radical changes are taking place in our atmosphere and climate; that the construction of great railroad-belts across the continent and the erection of a vast network of telegraph and telephone wires exert an influence upon the atmosphere, by disturbing the equilibrium of electric forces. The fact that tornadoes do not closely follow railroad and telegraph lines is not sufficient to disprove the soundness of this theory; and, whether true or false, the fact of the climatic change remains, and opens a vast field for further exploration by the electrician and the meteorologist.
Long-range predictions and weather forecasts may be safely indulged in, if made in a general way; but, when confined to fixed dates and certain localities, they have usually proved a hollow mockery, and brought ridicule upon the authors.
The United States Signal Service has proved to be quite reliable in its observations and predictions of approaching storms, and should receive due credit for its service rendered in protection of life and property. The benefits might be still further extended by a system of railway-express signals, operated in connection with it and by the direction of the Government observers at the different stations. Unfortunately, however, the warnings of this Service can not reach all concerned in time to be of value, nor can it protect in the hour of danger: as witness the tornado which visited the States of Texas, Mississippi, and Louisiana, on the 22d of April, in the present year, by which over one hundred persons lost their lives; also those which swept over a portion of the States of Missouri, Illinois, and Wisconsin, on the memorable evening of May 18, 1883. By this storm, sixty-five persons were killed and two hundred wounded in the State of Illinois alone; and yet the percentage of lives lost was small compared with the immense value of property destroyed.
As the matter now stands, the tornado seems to remain a problem that baffles science—a veritable despot in the economy of nature. The puny arm of man is powerless against it; no structure he can rear will successfully resist it, coming off unscathed in the conflict; and no device his mind can plan will turn it aside from its chosen course. Experience has amply demonstrated that the safest place in the hour of such danger is found in some subterranean retreat.