Great Disasters and Horrors in the World's History

by Allen Howard Godbey

Any one who has observed the waters at the junction of two streams, is familiar with the appearance of numerous tiny eddies or whirlpools formed at the point of junction. Such are perceptible also in every rapid stream, when the current, sheering sharply from a projecting point, is made in a measure to collide with itself. This is also the principle of the many tiny whirlwinds seen during the warm summer days: and such are also observable in winter, if there be snow enough to render their presence in the air clearly visible. Their results are most readily recognized in snow-drifts, where the wind meets some special obstruction. It does not often occur that a high fence is covered with a snow-drift: a great drift will be thrown up by it, but not against it: and the side next the fence will be curved inward, or concave. The wind strikes the fence and partially recoils, curving upward to pass over the fence. The drift is then built up between the wind and the current recoiling from the fence, and its inner curve shows the direction pursued by the rebounding current.

Now, when opposing air-currents meet each other on a large scale, the immense whirlwind that is produced is called a cyclone or tornado. It follows then, that if we would find any regularity or law in these unusual disturbances, we must know if there exists any permanent condition of atmospheric currents that is favorable to their generation.

That such a state exists, we have already learned. The great belts of calms that we have found between the trade-winds and the return trades and polar currents, are more appropriately called the zones of equinoctial storms. We have in them districts of general calms, with winds infringing upon either side. It is evident then that, as in the case of the fence, whose recoil-current curves the snow-drift, a whirling current of considerable magnitude may arise here at any time: hence, violent storms do arise in these regions more or less at all periods of the year. But we have seen that these zones of calms move slightly to the north or south with the course of the sun. It would then appear that at the equinoctial period, when they return from the mean position toward the extreme northern or southern limit, there would be opportunity for unusual disturbances, especially since the heavy rainfall of those periods would unusually affect the temperature of the atmosphere.

That is precisely what occurs. The equinoxes are marked by storms of unusual severity, and the influence of the sudden falls of rain is so great that some eminent men believe them to be nearly the sole factor in the formation of these storms. In one case they doubtless are. If a very heavy rain be decidedly local, there is low barometer at that place. Now, if on either side there be areas of high barometer, the opposing currents flowing toward the center of low area are sufficient to meet all the conditions necessary for a cyclonic storm. As the zone of calms is comparatively narrow, it is apparent that the diameter of the area of any storm, owing to the pressure exerted by the incoming currents of wind, must be still less. Hence, the cyclone center, at its time of formation, seldom exceeds one hundred miles in diameter. As it travels away from the compressing currents that formed it, it is clear that its centrifugal force must increase; hence, its area increases, and its violence correspondingly diminishes.

These facts refer to the unusually violent cyclonic storms, properly known as cyclones. But all low area storms are characterized by the upward spiral motion, though not strong enough in the case of ordinary summer rains and thunderstorms to be especially noticed. We shall see, by and by, how this spiral motion may result without the intervention of any strong opposing currents.

Why and how a cyclone travels, is a question that at once propounds itself. Its motion is in accordance with a fixed law, whose operation varies only as it may be affected by unusual peculiarities in the configuration of the surface over which it travels. The reason of the motion is not so easy to explain; neither is it easy to explain why heat expands objects: but its operation is none the less certain. And so the route pursued by any storm can be readily indicated in advance. It is not a matter of mere conjecture.

The motion of a cyclone or tornado is in accordance with the same law that governs the motion of planets around the sun. It can be illustrated in a very simple manner by the spinning of a top.

Spin a top on a perfectly smooth and level surface. It will be better if the peg of the top be blunt or round, so that there will be no tendency to settle steadily into some possible hole or depression.

Now, the instant any degree of steadiness is attained, the top begins to move in small curves. If it be spun on a marble slab smoothly coated with fine flour or sand, it can be made to record its motions, which may then be carefully studied. It will be found that the form of the curve is nearly the same with every start. It will describe a parabola, pause a moment, then describe a second, and so on.

The chief peculiarity of this separate curvilinear motion is that its direction is always in an opposite direction to that of the rotation of the top. If the top turn from left to right, it will move from right to left, and vice versa. The same tendency will manifest itself even if the peg of the top be placed in a slight depression or socket, so that the curve cannot be made. Then the upper portion of the top will incline to one side, and begin describing a curve: but, as before, in a direction contrary to the direction of rotation.