Shenandoah herald. [volume] (Woodstock, Va.) 1865-1974, 1892-09-02
WHIRL WINDS.
CAUSES OF AERIAL DISTURB
ANUE OFVARIOUS KINDS.
Zephyrs, Cyclones and Typhoons-
Pillars of Sand and Water
Created BY the Wind -
a Striking Case.

When they are large, for instance, 5OO
miles across and covering an area equal
to that of several of the large States, the
whirling character is not visible to a
single observer.
To him the wind seems to be straight
lined, but changing gradually in direc-
ton as the storm passes over. 1t Is only
when the observations Of many persons,
scattered over the whole area, are put on
a map that the whirling character is visi-
BILE.
Whrlwinds may also be of all degrees
of intensity, from one producing gen.
tie breeze to one producing heavy gales
which will founder ships or lproot the
heaviest trees.
The natural whirls in the free air are
not OF the nature of eddies, such as &C.
cur at the street corners in u city on a
windy day. These are due to the meet.
ing of two currents of air after passing
an obstacle; they are stationary, or
nearly so; depend on the speed and di-
rector of the wind, and rarely do any
more harm than that Of carrying off hat
or turning an umbrella inside out.
A truer type of the whirls that make
storms arc the dust-whirls over country
road or in hay field in hot, still
summer afternoon.
1t will be interesting to give brief
account OF the various members of this
family of whirls in free air. Tumultuous
or confused wbirlS, such as can be seen
in the smoke from factory chimney and
which occasionally occur in nature, will
be omitted; only the pure whirls will be
taken, though it must be remembered
that where these are large they will be
somewhat confused at the bottom, next
the earth, where the observers are sta
toned, because of the topography.
First come the dust whirls, hay geld
whirls, plowcd field whrls aud many
other small, welcomed ones occurring
on hot afternoons. They are very pretty
and interesting, and can be seen only
when dust, light hay or something OF
the sort is carried up, or when the whiri
is carried over a field OF timothy or of
other grain, when the swaying of the
stalks shows the shape of the base.
Similar whirls from over the hot coffee
Gun at the breakfast table and over
kettle of hot water, and may be seen
when the temperature Of the room per-
mits the steam to become visible. The
air next the ground in the one place, or
the hot liquid in the other, becomes hot
ter, and, therefore, lighter than the air
above. 1t is q thin stratum and strives
TO rise. This it does for some reason Ga
projecting stone up which it creeps, the
flight of a bird, bubble escaping from
the liquid surface, and many other
things), at one point. The air drains
through at this point rushes in from
around, and as it must generally rush in
equally from the sides, because they are
differently heated, or there is an OBJ
stacle, or the surface of the ground is
UNEQUAL, whirl is set up, and the whirl
once formed is likely to continue until
worn out by friction. They occur only
when the air is still, because when there
is wind the air is constantly mixed and
the hot stratum cannot form.
Next come sand and desert whirls.
These are like the preceding, only larger,
because formed on larger field and I'M
der more favorable circumstances. They
occur in arid regions in hot weather.
They may be anywhere from rod to
several rods in diameter and from twenty
to 1000 feet high. They are sometimes
compound, a score or more of small
whirls forming a whirling circle around a
common centre. They are very COM
mon in India, where they have received
the compliment of book devoted to
them. They sometimes carry up so
much sand in the Sahara and Arabia as
10 overwhelm those on whom the sand is
let fall. They also occur in the arid
regions of the United States. The
most striking case have ever seen was
in the Magdalena Valley, across the
mountains westward from Socorro, in
New Mexico. There, during hot day
in summer, they necessarily form at the
head of the valley in long, slender,
vertical column, perhaps 500 feet high,
and then travel down the valley toward
the little village OF Magdalena In the
bottom of the valley, over which they
sometimes burst, bringing to the inhab-
itants little puffs of contrary winds and
shower Of fine dust.
Then comes IN group OF stationary
whirls of the same general character as
the preceding, but tied down to one
point. Such are the whirls which some:
times form over volcanoes, rendered
visible by smoke and ash and the whirl.
winds that sometimes form over conaa-
grations. The latter can often be seen
when large and compact fire is made
in space which is fairly free from OBJ
structions.
So far the whirls mentioned have de-
pended on heat alone. They are in some
sort pure heat engines, and have no per-
petuating power after the beat is with