TORNADOES AND CYCLONES.
“O sad and mournful wind!
From what wild depths of human pain and sorrow
Could’st thou those tones of restless anguish borrow
As of a soul that dreams of no to-morrow,
O sad and mournful wind!
O, thou art fierce and wild!
Thy mighty chariot through the black skies lashing,
The cloud-shapes round the mountain-summits dashing,
The waves of ocean round the wrecked bark crashing--
O, thou art fierce and wild!”
Men find no difficulty in recognizing law and system in the phenomena
that are of constant or frequent recurrence. That which is most
difficult to explain, may pass without a serious thought so long as it
manifests no stupendous or sudden power. The water may wear away the
stone for centuries and its progress be unheeded by those who daily
visit the pool.
So all observe and admire the beauty and order that prevails in the
system of winds hitherto described. Their movements seem so simple and
natural, that people take them as a matter of course. Rather, we should
say, they may be depended upon with such certainty that the laws which
they followed were unheeded for more than six thousand years. Relying on
result, men gave themselves no concern about principle.
But in the sudden storm, the cyclone or tempest that comes sweeping the
land with hardly any warning, flooding and destroying, men find
mystery.
And who is not justly awed thereby? What other power so easily and
frequently wrecks and ravages? Who may point out its course or stay its
progress?
And indeed it would seem difficult at first to find any law or system
that controls the motion of the storm. If a rain storm always came from
the same direction; if unusually high winds always blew from the same
quarters, just as the moderate breezes of spring and summer can always
be expected from the same general direction, it would appear that there
was much greater subordination to definite law. But what can be more
perplexing than to have a storm blow violently from one quarter for a
time, and after a brief calm to blow with equal violence the other way?
Can such phenomena be explained by any principles hitherto discovered?
What is a storm? Strictly speaking, it is any marked or unusual
disturbance of the normal atmospheric conditions. There may be excessive
wind: there may be cessation of the customary winds. Two great classes
are found: cyclonic, or low area storms, and anti-cyclonic, or high area
storms. The former may be accompanied by heavy rainfall or snow; the
latter is usually noted for absence of either. It is with the low area
storm that we must deal at present.
This term is used to designate all storms which are marked by low
barometer, and therefore it is clear that such are accompanied and
partially occasioned by an unusual amount of moisture in the atmosphere.
The resultant commotion is usually extensive, the storm centre traveling
across the country; but occasionally the effects are perceptible only
for a short distance, the storm centre either breaking up or ascending
to the upper atmosphere.
By a cyclonic storm is signified a storm characterized by unusually low
barometer, and a wind system blowing spirally inward, as in a genuine
cyclone. They usually affect only the lower strata of the air. Quite
frequently they are broken up by striking low mountain ranges, such as
the Alleghany system: and often pass Mount Washington without making
their presence felt at the signal station on its summit. To what extent
they are influenced by or are due to the upper air currents is therefore
unknown, though not a few of the attendant phenomena indicate that the
latter are of no little importance.
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.
The common toy known as a gyroscope illustrates the last peculiarity
also. It consists of a wheel within a metal frame, which has a peg like
a top. If the wheel be made to revolve rapidly, the whole may be
balanced on the peg: when the frame will begin to slowly revolve in the
opposite direction: and if placed upon a smooth level surface, like the
top it will tend to describe the same course.
Still other illustrations of this principle are even more familiar than
the spinning of a top. Any one who has seen the game of soldiers in a
bowling alley knows that in order to make the ball turn to the left as
it moves forward, it must spin the other way; that is, with the hands of
a watch. To travel or curve to the right, it must spin in the contrary
direction. So in our “great national game,” base-ball, the pitcher
curves the ball any way he pleases merely by following this law. It is
not necessary to take into account, as many do, the return trades, as
occasioning the travel of a whirling storm; and the fact is, that the
cyclone frequently travels more rapidly than the ordinary wind moving in
the same direction.
Now, the motion of the planets is similar: rotating in one direction,
they travel in the other. So we find the general law is,
_All revolving bodies, left free as to direction, travel in a curve in a
direction opposite to that of their rotation._ This curve is usually
some form of conic section: an ellipse, parabola or hyperbola. The
planets, and some comets, move in ellipses. Some comets travel parabolas
or hyperbolas. And the parabola is the customary path of the cyclonic
storm. As the cyclone in the northern hemisphere rotates from right to
left, and in the southern from left to right, their paths must
necessarily be in opposite directions, as may be seen by the
accompanying diagram. So in either case, the direction of the path is
always away from the equator.
[Illustration]
As far as the United States are concerned, most non-cyclonic storms
originate in the Saskatchewan country, or along the southeastern slope
of the Rocky Mountains. By far the greater number pass over the St.
Lawrence valley. A small number are developed in the Gulf, or in the
Pacific: but these are much affected, often broken up, in crossing the
Rocky or Appalachian systems. The usual course is somewhat north of
east; but there are a few notable exceptions. The immense amount of
vapor wafted up the Mississippi valley induces some low area storms to
move southward from Manitoba into the upper Mississippi valley. In like
manner, the excessive moisture along our north Pacific coast causes
occasional storms to move southward from Alaska to Oregon.
But the course of a cyclonic storm, we have seen, must be different.
The accompanying diagram illustrates the fact that the wind blows from
all directions toward the center of the storm. As the storm revolves,
the wind would come apparently from the south for any one on the eastern
edge of the cyclone of the northern hemisphere. Hence, in the case of a
storm of large diameter, people in Richmond or Washington may often be
surprised by an apparent northeast gale, which reaches them before it
strikes New York or Boston. At the center of the storm is absolute calm.
So if a cyclone pass centrally over any point in the northern
hemisphere, a person at that place will find the wind blowing violently
from the southeast: then after an interval of calm, it will blow with
equal violence from the northwest. This will be the case if the path of
the storm has already turned to the northeast, so that its northeast
quarter may be called its front. If on the northwest course, however,
the apparently alternate winds would be from the northeast and
southwest. So one in the path of a southern cyclone would find the winds
proceeding from the same quarters; for though it revolves in the
opposite direction, its front or path is also in the opposite direction;
so in either hemisphere, the southeast or the northeast wind will be the
first felt by one directly in the track of the storm.
[Illustration: ROTATION OF STORMS.]
Another result of the path of a cyclone is that the direction of its
center from the stand-point of any observer is readily known. A glance
at the diagram shows at once that if any one within the storm area of a
cyclone of the northern hemisphere stands with his back to the wind,
the storm center, where the barometer is lowest, is invariably on his
left: but if he stand with his back to the wind of a southern cyclone,
the storm center is always on his right. Hence, if a vessel be overtaken
by a cyclone, the captain at once may know how to pass beyond its range,
by shaping his course at right angles to that of the wind. Thus, if in a
northern cyclone, he must sail to the right, supposing his back is to
the wind: in the southern hemisphere, he would sail to the left.
As an example of the expansion of the storm area in its journey, may be
mentioned the West India hurricane of 1839, which had, in the Antilles,
a diameter of three hundred miles, which increased to five hundred at
the Bermudas, and eight hundred on the parallel of 50° north latitude.
To draw again upon the illustration of the spinning top, it will be
observed that the curvilinear motion is extremely slow in comparison
with that of rotation, but increases as the rotation decreases. The same
law applies to the movement of cyclones. The slowest motion forward is
usually near the apex of the curve: and the progress on the ocean is
much slower than on the land. Traveling over the latter, the
irregularities of surface act in the case of the storm just as a rough
surface does in the case of the top. The motion may be accelerated, but
its regularity is lessened. So while at sea the parabolic path of the
storm is almost absolutely perfect, but on reaching the land its motion
is more rapid, and less regular, conforming somewhat to the
configuration of the surface.
To illustrate, take the great cyclone of August 16th to 22nd, 1888. This
started off Point Jupiter, Florida, with a rainfall of 2.2 inches in
twelve hours, while the rotary velocity of the wind was sixty miles per
hour. Its path across the Gulf of Mexico was a perfect semi-parabola,
curving northward into western Louisiana; but rapid as was the rotary
velocity, three and a half days were required for the journey across the
gulf. Meanwhile, it was rapidly widening: for within a few hours of its
reaching land, its eastern edge was assailing Mobile, Alabama, with a
south wind of fifty-five miles an hour. Almost at the same time the
western half was flooding Memphis and Vicksburg with an enormous
rainfall--almost four inches in twelve hours, at Memphis. By the morning
of August 21st, thirty-six hours after reaching land, it was central
over middle Tennessee and Kentucky; heavy rains fell over the entire
region. But by this time its eastern edge was in collision with the
Appalachian chain; while a heavy local rain at the northern extremity of
that chain created an additional diversion in a new area of low
barometer. So it left the hitherto parabolic route, and shot away nearly
at a tangent along the western Appalachian slope, passing from Tennessee
to Newfoundland in thirty-six hours, thus moving nearly three times as
rapidly as in the Gulf: while its violence, or rotary speed, was vastly
lessened.
This storm was one of the most destructive of the recent cyclones that
have swept our country, doing immense damage to crops, bridges, houses,
herds--in short, everything that can be seriously damaged by wind or
flood.
The damage in Louisiana alone was estimated at $500,000. But it was by
no means the most destructive of the West India storms.
An examination of the areas of calms, which are the hot-beds of cyclones
and hurricanes, shows that the region which produces the great cyclones
of the United States lies in the Antilles and Caribbean Sea. In the
Pacific the portion of the calm belt of the Tropic of Cancer causes the
ravages of cyclones or hurricanes originating there to be felt chiefly
in Japan and China. The storms of the Pacific arising in the equatorial
calm belt, are most violent in the East Indies, and the southern
peninsulas of Asia. As these regions are much warmer, and consequently
the atmosphere may hold a much greater quantity of vapor, it follows
that cyclones in that quarter much exceed in violence those of our own
land.
Such are the general laws of these terrible disturbances of nature, as
ascertained by years of careful observation. In the United States, our
Signal Service, with well-equipped observatories at important
localities, is able to make these principles of practical use: to detect
the incipient storm and mark out its path, ere it strikes its fiercest
blow.
It should be observed, ere leaving this topic, that a few would-be
prophets have maintained that not only great storms, but also
earthquakes, volcanic eruptions, tidal waves, etc., are due to planetary
influences. Observing that the most violent hurricanes occur near the
equinoctial period, they argue that the equinoxes of the planets ought
to also disturb the earth. They ignore the fact that as to our own
equinoctial disturbances, the change in the relative position of the
earth and sun is sufficient to produce change in the location of heated
air-currents and consequent storms. They seek to find in the Equinox
Absolute, some strange mysterious magic, some inexplicable power or
_Deus ex machina_, whose business it is to get up a disturbance here on
earth at every possible opportunity, no matter in what planet he may be
for the nonce located.
But it is difficult to rid any man of his hobby. In the question of the
equinoxes of other planets, their recurrence is of sufficient frequency
to allow the weather-crank full play for his imagination. Two of the
major planets lie within the earth’s orbit, and their more rapid course
about
[Illustration: WATER SPOUTS AT SEA.]
the sun results in there being an equinox in one or the other of them
about once in each month. So no matter in what month a great storm may
occur, the enthusiast can point out that a neighboring planet is at or
near an equinox.
A careful examination of the equinoxes of the inner planets for a period
of fifteen years shows that the number occurring in the month of April
was 22 per cent. above the average occurrence for any month: whence, it
would appear that the disturbances at that period ought to be equally in
excess. But as a matter of fact, storms on the earth are most numerous
and violent at the time of the autumnal equinox--September and
October--when no such departure from the average of equinoxes of the
other planets appears.
If planetary influence were the cause of our storms, it would be
reasonable to suppose that disturbances would be greatest when the
planets are nearest to the earth: but the advocates of the theory do not
seem to consider this a factor at all. Nor could the planetary equinox
theory account for the fact that storms of peculiar character always
originate in the same regions. For instance, why do cyclones always
originate near the tropics and move away from the equator? If the
planetary equinoxes produce violent earthquakes, why are they so partial
to North America as never in our whole history to have given us a very
serious shaking up? Why is it that of the hundreds of recorded tornadoes
of the past century in the United States, only one has ever occurred
west of Dodge City, Kansas? Clearly the adherents of the equinoctial
theory will have to admit local terrestrial conditions that modify all
their theories: and to make such an admission will be, in the end, to
give up the fight.
The writer knew of a boy who wasted a pound and a half of bird-shot in
trying to kill a small owl. The game was finally secured, and the young
Nimrod discovered a hatful of feathers with the body of a robin--and of
no earthly use.
Attacking the planetary theory is of little more use. But the theory is
the resort of many would-be weather prophets, who needlessly alarm the
ignorant with their gloomy forebodings.
In a country as large as our own, any sort of weather is a very safe
prediction to make for any day in the century, as minor rains and cloudy
seasons and small storms are merely local. Any sort of prediction would
be nearly sure to hit some portion of the country; and one who is so
disposed can easily win a cheap notoriety and gain scores of
testimonials as to the correctness of his predictions. Every unusual
catastrophe produces a brood of these gentry who are eager to make the
trial. But those who endeavor to indicate the exact locality where any
great disturbance is to take place, meet discomfiture with a uniformity
that ought to be discouraging. The work of the Signal Service is as
carefully done as may well be: yet its best men assert that an average
of 90 per cent. of correctness in their prognostications is unusual,
because of the extremely small areas covered by local disturbances.
Rainy weather announced for western Missouri may be correct every time
for Kansas City, but be 10 per cent. in error for Nevada, Missouri. When
those whose time is devoted to the weather can not always be correct, it
is useless to listen to charlatans.
A careful study of sun-spots with relation to storms has been made of
late years. The fact is elicited that the spots seem to have a definite
connection with electrical disturbances: but while there are numbers of
coincidences between unusual sun-spots and great storms, the number of
striking exceptions seems equally great. Hence, it can not be fairly
inferred that there is any definite relation between them. And so far
as electrical phenomena on the earth are connected with storms, they
always appear as dependent upon rather than productive of atmospheric
currents. Indeed, the most remarkable electrical disturbances occur at
times when no atmospheric current is prevalent. The most beautiful
electrical display, the aurora, appears when the air is abnormally still
and unusually dry. The necessity of the latter condition accounts for
the fact that it is usually observable only in cold weather and occurs
with great frequency and in remarkable brilliancy in the polar regions.
It results from electric currents passing through extremely rarefied and
dry air, and may be produced on a small scale artificially.
Poe was right when he held that many things remain long secrets by
reason of their very simplicity. Six thousand years steam hissed and
fumed in men’s faces, and tilted the kettle lid, before they learned its
expansive power. Six thousand years the lightning flamed and roared
before man realized it could be made one of his most obedient servants.
Six thousand years he cudgeled his wits to discover the secret of the
wind: yet when he made a fire within his house, he closed the door to
prevent unpleasant draughts of air. And so he continues, constantly
endeavoring to find some strange mystery in the things that are
dependent on simplest laws.
There was a time when men stood aghast at small-pox, cholera, yellow
fever, and many similar calamities, and spoke with bated breath of the
“mysterious visitations of providence,” the “scourge of God,” and so on.
When the Turks once besieged a plague-stricken city, a comet appeared in
the sky. The pious inhabitants prayed “O Lord, deliver us from the
devil, the Turk and the comet,” and usually such people believed such
plagues were the judgment of God on them for their sins. Modern science
holds that about the only sin the Lord punishes in that way is the sin
of filthy streets, or back-door cess-pools. When man has once learned
the means of control and prevention, evils lose their mysterious
witchery.
On the other hand, let the laws of any force in nature be every so well
understood: yet, so long as they are beyond the control of man, they
will retain for him an eerie uncanny fascination. The pigmy has
harnessed the steam and chained the lightning: but when the storm clouds
lower and the forests moan, the sea roars and the lightning glows, he
stands in fear and awe before a power whose might he but vaguely
comprehends. He may know of the winds, whence and whither bound; but
when the Stygian darkness has passed on, leaving wreck and ruin, want
and woe, desolation and despair, shattered homes and hopes, and bleeding
hearts, this knowledge of law is, for the nonce, forgotten, and the
hurricane is transformed, in his disordered vision, into a demon of
wrath, or caprice; or he speaks, hesitatingly it may be, of the
mysterious dispensation of an inscrutable providence. But in the mighty
wind, as in the soughing breeze, there is only obedience to universal
law. But when the Author of law displays his power, man’s instinct,
however unwilling his reason, acknowledges a God.