The weekly pioneer and Democrat. [volume] (Saint Paul, Minn. Territory) 1855-1865, 1860-07-13
The Great TOrnadOes.

writes as follows in the Cincinnati Gazette
of the great tornadoes
A few facts in reference to that class of
tornadoes which have been so prevalent this
season, may prove interesting to your nu~
merous readers. They are the results of
careful observations for the past fifteen
years: The heavy storms in the Mississippi
valley, and indeed, of the Atlantic coast,
are found in the great atmospheric current
from the southwest. This current is doubt
less the atmosphere from the tropics on its
way to the north pole, in exchange for the
cold air of that region, which, in our north
and north west winds, passes back to the
equator.
A knowledge of this great system of at
mospheric interchange is necessary for an
understanding of these violent disturbances
which prevail in this and lower ATTITUDES.
pass over, as not pertinent to the purpose in
hand, all the notifications to which these
currents are subjected at certain ATTITUDES,
by the action of causes not yet fully under
stood.
Of the existence of these currents there
be no doubt. Their Interruptions, their
conflicts, the sliding, now Of this, now of that
over the other, all these are questions which,
however important, need not be introduced
here.
The great fact is this: Our heavy rains
generally are found in the track of this
southwest current and our tornadoes, with
scarcely an exception, are found imbedded
in it, and moving along with it. The rea-
son of this is obvious. 1t is a warm and
moist current, and, when cooled sufficiently,
will give out that moisture.
One more fact in reference to this cur
rent: As it sweeps towards the northeast,
it curves gradually more and more to the
east. On large scale this is due to the
motion of the earth on its axis, but in our
local storms, to the pressure on their north
ern borders made by the northwest current.
This accounts for another fact: that our
tornadoes, when traced considerable dis.
lance, move in curve line bending towards
the south and sometimes near the end of
their course the direction is south of east.
The great tornado of January, 1854, so de-
structive at Brandon, Ohio, had direction
at that place N. "a degrees E. In western
Pennsylvania, where it spent its force, the
direction was little south of east. The
south west current, in which it was embed
ded, was traced by the writer from Ar
kansas, through Southern Illinois, Indiana,
and through Ohio into Western Pennsylva.
mia. All along this track it was so warm,
though in January, as to require no fires ;
while at the same time, in Iowa, Northern
Illinois and Indiana, the thermometer was
either below or little above zero. This
leads me to notice another fact, very signi-
icant in explaining these violent disturb
ances. These storms are bordered on the
north by a cold wind from the northwest.
This cold wind presses upon the warm cur
rent from the southwest, gradually defects
it eastward, mingles with it, and being the
heavier finally slides under it. All these
storms, as every observer knows, are fol-
lowed by cool northwest winds. Such was
the case after the Cincinnati tornado of
May 81 and for eight days subsequent to
the almost unparalleled violence exhibited
at Camanche, northwest winds, uncomforta-
bly, cool, prevailed throughout this region.
The tempest does not make the northwest
wind which so generally succeeds it, nor has
it much influence in cooling it. The evapo-
ration after a shower does, of course, cool
the air somewhat at the surface of the earth;
but the condensation which made the shower
also gives out heat. The northwest wind,
and the moist and warm southwest, main
tain in this valley, owing to the topography
of the country, peculiar and very close
relations. They come very sharply into
contact-the one very cool, from its
frozen home-the other very warm and
moist, from the Gulf or the Pacific. All
the conditions necessary to produce violent
connections in the atmosphere are present,
and the result is what every meteorologist,
knowing these conditions, would expect.
The writer does not mean to attribute
these tornadoes, some of which are almost as
violent as blast from huge cannon, to
the meeting, merely, of the two currents re-
ferred to. l mention them as facts, and
very important ones; but the full explana-
ton of these strange phenomena meteorolo>
gical science cannot yet give.
The writer does not intend to enter into
any labored description of the various and
combined motions of the wind in tornado.
The motion is substantially made up of
three elements : LIST, the ascensional velo-
city; I'd, the velocity of rotation, and Sd, of
progression.
The velocity of rotation is usually the
greatest, and to it the destructive effects
seem mainly due. From thirty to fifty miles
per hour is the usual rate of progress, while
the rotation may vastly exceed it.
From some calculations upon the force of
the wind in the Brandon storm, the rotation
could not have been less than liz miles per
hour, while the progress was only 45 per
hour. At the rate of 172 miles an hour
the velocity is one.fifth that of cannon
ball.
The Cincinnati storm was distinguished
for its breadth, and especially for high
progressive velocity. In this latter respect
it stands pre-eminent. The progress was so
rapid as to obscure the rotation, and to rem
der it difficult in some parts to detect it at
all. From the cursory examination which
the writer has yet been able to give, it
seems probable that if there were general
whirl reaching across the track, it was, at
the surface of the earth, broken up into
several subordinate whirls, at one time act
ing separately, again commingling either in
conflict or to unite their forces in more
deadly energy. This irregularity is just
what any one, acquainted with the nature
of elastic fluids, would expect under the cir
cumstances.
No tornado of considerable breadth could