UNDER the above title Lieutenant John P. Finley of the United States Signal Corps has written a most entertaining and valuable book, the fruit of years of careful study of the peculiar characteristics of this much dreaded class of windstorm. Much of the matter contained in the volume appeared some time since in the columns of The Insurance Monitor, attracting wide attention. In its present complete form the work will doubtless quickly take rank as a standard authority upon the subject of which it treats, equally interesting to the scientific reader and helpful to the layman who simply seeks to know how best to protect his life and property against the bounding, gyrating aerial visitor whose all too frequent appearances he so justly dreads.
* Tornadoes. What They Are and How to Observe Them ; with Practical Suggestions for the Protection of Life and Property. By John P. Finley, M. S., F. S. Sc, New York : The Insurance Monitor. 1887.
“ For over two hundred years past,” says Lieutenant Finley, “the scientific records of this country have furnished information concerning these storms. It is the same fearful story, year after year, of destruction and death, and the records are now sufficiently complete to show beyond all contradiction or exception that tornadoes are indigenous to this country. They belong here because our geographical position and the topography of the country are altogether favorable for the conditions which give rise to their formation. No other country in the world is scourged by them as is the United States of America. If our broad expanse of country was cut up by mountain ranges running in every direction, forming a network over the vast plains of the West, and cutting up like a checker board the great valleys between the Appalachian and Rocky Mountain ranges, then topographical conditions would intervene and present formidable barriers to the direction and eflect of surface currents. These conditions, if they were present, would well nigh rid the country of the funnel-shaped cloud.” But in the greater part of the United States there exist no natural barriers against the development of the tornado, and we are told that the populous region of our country is forever doomed to suffer from its ravages. “As certain,” says the author, “as that night follows day is the coming of the funnel-shaped cloud,” and a knowledge of the tornado and the needful precautions to be taken for purposes of safety, should be as familiar to the people of the tornado distiicts as a knowledge of the ordinary methods of fighting fire.
Continuing, Mr. Finley remarks that “in spile of all that has been written and published about tornadoes in the press, in scientific journals, and through the Signal Service, much confusion prevails regarding the application of the term and the distinctive character of the storm. This confusion leads to a most unfortunate disregard of certain necessary provisions for safety which should not be neglected by people residing in the tornado districts. Under the head of ‘ wind-storms* there are various atmospheric phenomena, severally designated as tornadoes, cyclones, hurricanes, whirlwinds, waterspouts, hailstorms and thunderstorms, which are essentially distinct in their chaiacieristics.’’ He then briefly reviews the different classes of windstorms, cyclones, hurricanes, whirlwinds, waterspouts, hailstorms and thunderstorms, following with a special discussion of the tornado, as follows ;
The tornado is truly and invariably a land-storm, which wc find possessed of the following prominent characteristics: A path varying in width from a few yards to eighty rods. The general direction of movement of the tornado-cloud is invari ably from a point in the southwest quadrant to a point in the northeast quadrant. The tornado-cloud assumes the form of a funnel, the small end drawing near to or resting upon the earth. This cloud, or the moving air of which it is the embodiment, revolves about a central, vertical axis with inconceivable rapidity, and always in a direction contrary to the movement of the hands of a watch. The destructive violence of the storm is sometimes confined to the immediate path of the cloud, as when the small or tail end just touches the earth. While, on the othei hand, as the body of the cloud lowers, more of it rests upon the earth, the violence increases and the path widens to the extreme limit. The tornado with hardly an exception occurs in the afternoon, just after the hottest part of the day, and generally disappears before the going down of the sun. The hour of greatest frequency is between 3 and 4 r. M. A tornado very rarely, if ever, begins after 6 » M., but a tornado commencing about 5 I*. M. may continue its characteristic violence until 8 p. M., which only means that the tornado-cloud may be traveling after 6 l M. or after 7 P. M., but it does not develop, that is, make its appearance for the first time, after those hours. Without the path of destruction, even the shortest distances, at times even along the immediate edge, the smallest objects often remain undis -turbed, although a few yards distant the largest and strongest buildings are crushed to atoms. At any point along the storm’s path, where there is opportunity afforded the tornado-cloud to display its power, the disposition of the debris presents unmistakable signs of the revolving, right-to-left action of the wind. The violence and intensity of the destructive power increases directly as you pass from the circumference of the storm to its centre.
Observations with the barometer are of little practical value at anyone point, whether made before or after the tornado-cloud has formed or while it is approaching. Such observations will not indicate its approach, however near the position of the instrument embraced between March and October. The months of greatest frequency are May and July. There are exceptional instances, in a long series of years, where tornadoes have been reported in every month of the year. They may, and sometimes do, occur in some of the Southern States during the winter and spring months. Taking the whole United States together and averaging the dates of occurrence for a long series of years (over 200). it is found that the region of greatest frequency embraces the States of Kansas, Illinois, Missouri and Iowa. Of all the States i.i the Union, Kansas and Missouri rank the highest in regard to frequency.
Again he says :
What is a tornado? In defining this storm it would seem almost a necessity to rehearse its long line of striking characteristics, but this, in the common acceptation of the term, would not strictly be a definition. For the sake of brevity, we will state that the tornado is that form of atmospheric disturbance which takes the outward, visible fashion or figure of a funnel-shaped cloud, revolving about a vertical axis from right to left* with an inconceivably rapid movement and an immensity of power almost beyond calculation.
CONDITIONS OF Formation.—These may be divided into classes. First, those within the reach of and which may be known or investigated by an isolated observer. Second, those conditions only to be witnessed and analyzed by the intelligent and practiced eye of the student of the weather map. To the single observer, located mayhap at his farm home, the workshop, or the store, there are important atmospheric conditions which he may carefully watch and study with profit, viz. : the gradual setting in and prolonged movement of the air from the north and south points ; the gradual but continued fall of the thermometer with a prevalence of the northerly currents, or a rise with the predominance of the southerly. If the northerly currents are the prevailing air-movements at your place of observation, the atmospheric disturbance is forming to fhe southward, but if the prevailing air-currents are from the south the storm is forming to the northward of your location. Carefully study cloud development, color as well as form, also manner and direction of approach. The opproach of the cirrus cloud (perhaps at a height of six to eight miles) from the southwest is very significant, and is the first evidence of the gradual but certain advance of the upper southwest current, which eventually plays so important a part in the development of the tornado-cloud. Clouds are but the embodiment of air-currents, yet they are full of meaning. A study of the upper currents of the atmosphere would be impossible without their manifestations, and that, too, in a variety of forms. Without cloud formation, the face of the sky would become a blank, and intelligent reasoning thereof a superhuman task.
Wind direction, temperature and clouds are the proper subjects of observation and thought by the isolated observer. The barometer is of little, if any, importance in this line of inquiry. If you cannot compare your barometric observations with those taken at near or distant points and at the same moment of actual time, they are of no practical moment, even though your instrument is a standard one and your corrections for temperature and elevation carefully applied. The storm you are watching for (the tornado) is an extremely local affair, whereas the barometer indicates general changes, affecting a large extent of country. Your instrument, if a standard, docs not lack possession of the delicate sensitiveness requisite for all the purposes of its construction, but if it were placed in the immediate track of the tornado-cloud, it would not indicate its presence until the crash of th; storm was upon the instrument, when of course it would be too late. Barometrical observations appear to advantage and are absolutely necessary to a successful consideration of the meteorological conditions of tornadoes from the standpoint of the weather map. From this panoramic view ol the situation a vast extent of country can be most carefully watched from hour to hour, for days, weeks, or months. Atmospheric conditions on opposite sides of the probable course of the storm can be watched from their inception, and any relation easily detected and analyzed. From a study of the weather-map it has been found that the formation of what is termed a barometric trough or elongated area of low pressure (where the barometer stands below the normal for that region at the hour of observation) precedes the occurrence of tornadoes in the Lower Missouri Valley or adjoining States to the south and east. This low-pressure area assumes the form of an ellipse and generally extends from southwest to northeast between northern Texas and the Upper Lake Region. Such a depression may lie between the Central Mississippi Valley and the Iower Lake Region, trending northeastward just south of Michigan and over the Ohio Valley. The major axis of either of these depressions is easily estimated. while the minor axis may be stated as generally varying from 300 to 500 miles. To the north of the major axis, even to a distance of several hundred miles, the winds are found to proceed from any or all points between northeast and northwest with comparatively low temperatures, accompanied sometimes by a cold rain, or even snow. South of the major axis, and generally to a greater distance, the winds come from any or all points between southeast and southwest, accompanied by comparatively high temperatures, high humidity, and often dashes of quite heavy rain.
As these conditions continue to prevail there is a growing contrast of temperature to the north and south of the major axis, owing to the long-continued movement of the atmosphere from opposite directions, such movement eventually affecting the disposition of air in the warmer regions of the extreme south and likewise the colder regions of the extreme north. The contrast of temperature now naturally increases with marked rapidity, and the formation of clouds commences in earnest. Huge masses of dark and portentous appearance bank up in the northwest and southwest with amazing rapidity, and soon the scene becomes one of awful grandeur. The struggle for mastery in the opposing currents is thus indicated by the gathering cloud formations. The condensation of vapor from the extremely humid southerly currents by contact with the augmenting cold of their struggling opponents continues. It increases rapidly. Finally, when resistance to the unstable equilibrium can no longer be maintained (controlled by the rate of temperature change and rapidity of condensation), the opposing forces are, as it were, broken asunder, followed by the upward rush of huge volumes of air. The outward indication of this event is first shown in the whirling, dashing clouds over the broken surface of the heavy bank of condensed vapor, forming the background. A scene not easily depicted or realized by one who has not witnessed it, but never to be effaced from the memory of the actual observer. There is an awful terror in the majesty of the power here represented, and in the unnatural movement of the clouds, which affects animals as well as human beings. The next stage in the further development of this atmospheric disturbance is the gradual descent of the funnel-shaped cloud from a point apparently just beneath the position of the enactment of the first scene. The tornado is now before us, not fully developed, but soon to acquire that condition when the terrible violence of its power will make the earth tremble, animals terror-stricken and men’s hearts quake with fear.
* A* you would turn a nut only a bolt, point downward.
The list of premonitory signs includes a sultry, oppressive condition of the atmosphere and the appearance of a number of various and strange cloud formations:
Sometimes these peculiar clouds extend from the southwest through the west by the north to the northeast. More frequently, however, they form in the northwest and southwest, sometimes commencing first in the former quarter and then again in the latter, but in either case they are equally significant. The marked peculiarity of the clouds is found to occur not only in the form, but in the color and character of development.
The sudden appearance of ominous clouds, first in the southwest and then almost immediately in the northwest or northeast (perhaps the reverse in the order of their appearance), generally attracts the attention of the most casual observer, and frequently overcomes him with astonishment. In almost all cases these premonitory clouds are unlike any ordinary and usual formation. If they are light, their appearance resembles smoke issuing from a burning building or straw-stack, rolling upward in fantastic shapes to great heights. Again, like a fine mist or quite white, like fog or steam. Some persons describe these light clouds as at times apparently irridescent or glowing, as if from their irregular surfaces a pale, whitish light was cast.
The dark clouds at times present a deep, greenish hue, which forbodes the greatest evil and leaves one to imagine quite freely of dire possibilities. Again, they appear jet black from centre to circumference, or, in a change of form, this deepset color may only appear at the centre, gradually diminishing in intensity as the outer edges of the cloud or bank of clouds are approached. Sometimes these dark clouds, instead of appearing in solid and heavy masses, roll up lightly, but still intensely black, like the smoke from an engine or locomotive burning soft coal. They have been described as of a purple or bluish tinge, or at times possessed of a strange lividness. Frequently dark green, again an inky blackness that fairly startles you with its intensity.
The illustrations which we have selected from the many contained in the book, represent three stages of the great tornado at Ercildoun, Pa., on July 1, 1877, and two views from points twenty miles apart of a tornado which occurred near Redstone, Davison county, Dak., August 28, 1884. The Ercildoun tornado formed at about 2.30 P. M., and swept due east for about twenty miles, destroying over $40,000 worth of property and injuring many persons. The width of its track was 150 to 300 feet, and the diameter of the tornado cloud fifty to seventy-five feet. The Dakota tornado destroyed all property in its path and killed several persons. The two sketches, made by men unknown to each other and at such a distance apart, are valuable for the corroborative evidence which they give each of the other.
Of the characteristic motions of the tornado cloud we are told that they number four, described as follows :
No. I. is called the whirling or gyratory motion of the tornado-cloud, which is invariably from right to left, or against the course of the sun. From the peculiar character of the formation of the tornado-cloud, this motion is in all probability the first evidence of the existence of the cloud, and should therefore be placed first in order of consideration. Above all other motions, this is attended with the greatest violence, and its velocity of movement is far in excess of any of the others. This gyratory motion forms what is termed the vortex of the tornado-cloud, within which the velocity of the centripetal currents of air is almost beyond conception. Many efforts have been made, but most of them altogether fruitless, to estimate the rate of progress of these currents, and velocities ranging from 100 to 800, and even xooo miles per hour, have been deduced ; the two latter are the extremes that have been ventured upon, and of course are not reliable, while in the majority of instances more trustworthy determinations have ranged between 100 and 500 miles per hour. Theoretical velocities of over 2000 miles per hour, based upon certain assumed atmospheric conditions, have been deduced. Such velocities are mathematically possible, but not meteorologically probable. * * * *
No. II. is called the progressive motion of the tornado-cloud, the motion which determines the cloud s track from one point to another. The rate of progressive velocity ranks next in order to the velocity of motion No. I., although it is at all times far below the high degree of the latter.
The rate of progress of the tornado-cloud is subject to great variability throughout the path of any one storm, although on the average tornado-clouds possess a moderately uniform velocity of progression. Some observers have indicated the movement by the following expressions: “All in an instant.” “ Gone in a moment.” ” Quicker than thought.” “ Without a moment’s warning.” ” It moved no faster than a horse gently galloping.” “I just saw what it was and then all was over.” ” Before I had time to turn about in my tracks it flashed by me.” “ It seemed to remain almost motionless, as if held to the ground by some mysterious force.” “I shuddered, held my breath, and the monster had vanished.” “It seemed to move no faster than I could run.”
These estimations of velocity are not to be taken altogether literally. The circumstances under which the impressions were received must be considered, viz.: undue excitement or abject terror. However, the comparative results are important, and to a certain extent reliable. Through them the reader will at least not be led astray in his conceptions of the awful grandeur of the panorama, or fall into the fatal mistake of encouraging a belief that the tornado is not what the united experience of all observers has portrayed it. * * * *
No. III. is termed the rising and falling motion of the tornado-cloud, the character of which finds definition in the following expressions from various witnesses: “ The top of the cloud seemed to pop up and down, and then to rush forward.”
It bounded over the ground like a ball.” “ It was the strangest jumping and flopping object I ever saw.” “At times it seemed to lash the earth in terrific fury with its huge tail.” “ It came along, popping up and down in a most fantastic way.” ” Rising up like the uncoiling of a huge rope, it cut loose from the earth and passed over us with a horrible whizzing sound.” “Ever and anon it would shoot directly upward from the earth, sometimes with great rapidity, and then again quite slowly, each time dashing to the surface with apparent renewed vigor.” It is perhaps clearly seen that this is a distinct motion with striking peculiarities which define its character. Sometimes, upon the lifting of the tornado-cloud from the earth, it does not again descend fora distance of several miles, at times making the return movement or descension twenty or thirty miles distant, the intervening space proving a complete blank in its track. More frequently, however, these gaps are from one to five miles in length. * * * *
No. IV. is called the zigzag motion, or swaying from side to side of the central line of cloud movement. This motion is sometimes quite suddenly performed, but generally it is a moderately slow movement and one that can be watched and easily identified. It seems to occur most frequently just as the tornado-cloud touches the earth in completing the last act of motion No. III. In completing the extent of a single act of this motion, the tornado-cloud will diverge about an equal distance on either side of the central line of movement, though these tangents to the major axis are not necessarily of equal length. * * * *
The remainder of the volume is devoted to clear and simple directions for protection, and to illustrated descriptions of noteworthy tornadoes, and of the tornado-cave for the design of which John R. Church, a Rochester (N. Y.) architect, was recently awarded a prize of $200 by a Western insurance company. A number of valuable statistical tables are also given, a carefully prepared “scientific rfisume of tornado characteristics,” and much other miscellaneous information, besides two charts, one of which, showing the geographical distribution of the tornadoes observed in the United States during the past 125 years, indicates in a remarkable manner the influence of topographical conditions upon the frequency and destructiveness of these storms. Upon the whole, this little book is a timely addition to the literature of the day, and we think is destined to be widely read.