Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1881-05-25

disturbed Dy Sllgnt local Changes Oh ttin-
perature causing the under strata of air TO
burst up through the everything strata. A
cycloie is usually a broad, fiat, grating
disk of atmosphere, very many times
greater in width than in altitude; a tornado
may be regarded as column of gyrating
air in which the altitude ls several times
greater than its diameter. The enormous
velocities of the ascending currents in a
tornado appear to be caused by the differ
ences between the gyratory velocities above
and those very near the earths surface.
The former largely prevent the air from
pressing in to fill up the partial vacuum
near the center, while the smaller gyratory
velocities near the earth allow it to rush in
there to supply the draught. The tenden-
cy of friction Is constantly to use up the
energy of gyration so that the tornado can
not continue very long. The ascending
currents carry up an enormous amount OF
aqueous vapor into the upper regions of
the air, where it is condensed and produces
the heavy rains observed in connection
with tornadoes. An ascending current OF
60 meters a second, which cannot be un,
usual in tornadoes, would furnish, under
extreme conditions of air saturat.on, four
inches of rain In a minute, If 1t were to
fall directly back. With such an ascend
ing velocity, however, no ram could so fall.
1t would be thrown outside the vortex,
giving an immense though lighter fall OF
rain over larger area, especially II the
tornado in its regular progressive motions
should remain stationary or nearly so for
z
ascending current is not so great that the
water is all carried up to where the cur
rents are outward from the vortex, and yet
great enough to prevent its falling back,
there may be in the lower part of the cloud
vast accumulation of rain, prevented from
falling by the ascending currents and nom
being dispersed by the infiowing currents
from all sides toward the vortex. When
the sustaining energy of the tornado is ex-
haus.ed by friction or by the weight CT
wafer accumulated in the cloud, the water
is liable to fall in a mass, causing what is
called a cloud burst. This is especially
liable to occur In mountainous regions, for
contact with a mountain must greatly in
terfe-e with the gyratory motion OF the
tornado and the inflowing currents below,
and tend to break up the system at once
and let the whole load of water drop sud-
denly.
When the ascending current carries the
vapor into the region of frost-which is at
a lower altitude within the gyratlng funnel
than outside of 1.-THE condensed vapor is
converted into hail. The small hailstones
may then be kept suspended near the base
of the snow cloud and enlarged by the
additions of freezing ram. In this way
compact homogeneous hailstones of ordi-
nary size are formed. At the height of
1000 Yards the air has lost more than half
its density, yet an ascending velocity OF
twenty yards a second. which must be no
unusual one in tornadoes, would sustain
even at that altitude hallstones of consider
able size. 1t is not necessary that the
hallstones should remain in the freezing
region long time. or remain stationary.
They may be carried from this vortex out
where the ascending current is small, and,
dropping down some distance, may be
carried into the vortex by infiowing cur
rents and again thrown up to the region of
frost. The nucleus of large hallstones is
usually compacted snow. A small ball of
snow saturated with water Is carried higher
and freezes; and being of less specific
gravity than compact hail 1t is kept where
it receives a thick coating of ice from the
unfrozen water dashed against 1t, and after
wards falls to the earth, either at distance
from the vortex where the ascending our
rents are weak, or near 1t after the uprush
has been sufficiently exhausted. Some
times, as In the case of the cloud burst, an
almost incredible amount of accumulated
hail may fall in a short time, when the
energy of the system is suddenly spent.
The formation of large hailstones by
coHcen.ric layers of clear ice and white
snow, laid on like the coats of an onion.
will be readily understood from the fore
going. As many as thirteen layers have
been observed in large hailstones, showing
that they must have been made of half a
dozen circuits, being successively thrown
out of the frosty vortex above and sucked
IN below by the inflowing currents, each
time adding to their coatings OF snow and
ice before their final fall to earth.
When the tornado is very small in the
area covered by the gyratory motion, a
land spout or a water spout is formed, as
it may happen 10 occur on land or at sea.
In these the gyratory velocity diminlshes
with distance from the center. Their de-
structive habits are sudden and often great,
but the area of violence is small. In the
center of waterspout, as In that OF a
tornado in tull force, no rain falls or water
descends in any form, though a heavy
shower often falls in the vicinity. On
land dust and light substances are carried
up, and as they are being collected from
all sides by inflowing currents toward the
vortex below, they assume the form Of a
cone, which meets the descending spout,
falling apparently from the clouds, and
thus give the whole phenomenon the ap-
pearance of an hour glass.
The observed dlameters of waterspouts
range between two and two hundred feet
or more, and their heights from thirty to
fifteen hundred feet, sometimes very much
more; but none of these observations can
be regarded as at all exact. With a high
temperature and very low dew point Mr..
Ferrel calculates that water spout might
reach a mile in Height, but such conditions
must occur rarely. Waterspouts are often
observed to drop down from a cloud in an
incredibly short space of time, and to be
drawn up again in the same manner; but
this is all an illusion. When the gyrations
are such as 10 not quite reduce the ten
sion and temperature in the center, so as
10 condense the aqueous vapor and make
it visible, a very slight increase at once re-
duces the temperature sufficiently, and the
spout appears from top to bottom almost
instantaneously. Just the reverse of this
takes place, when the spout breaks, and il
seems to be drawn up instantly; it is dis
solved, not lifted. Tornadoes and water.
spouts originate only in an unstable state
of equilibrium of the air, which require:
an unusually rapid decrease of temperature
with increase of altitude. This can take
place only when the strata nearest the earth
are unusually heated; accordingly they
never occur at night, or in the winter, and
but rarely In cloudy geIther. Ii any aglia
tion of the air, such IS that arising from
the discharge of cannon, tends to break UP
these meteors, then any considerable dis
turbance of the air from any cause must
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