The San Francisco call., 1896-05-30
Light, Moist Airs of the Surface
Meet Cold and Dense
Currents.
ROTARY MOTION IMPAIRED.
Premonition of Peril in the Hush
That Precedes the Tor.
nado's Burst.

The tornado which wrought such dis
aster in st. Louis last Wednesday evening
was one of several developed by the
cyelonic conditions which have prevailed
for the past two weeks in the great basin
lying between the Allegheny Mountains
on the east and the Rocky Mountains on
the west. A cyclone may have breadth
of 500 miles, but the tornado, q fierce
storm often possessing rotary motion, is
developed within the area of the cyclone.
Sometimes a powerful wind attaining
velocity of seventy or eighty miles an
hour and causing great damage is called
tornado, but it is not so in fact.
Mr.. Hammond, the United States
Weather Bureau in San Francisco, was
stationed at st. Louis for many years and
had ample opportunity to study atmos-
pheric disturbances in that region of the
Mississippi Valley. His views concerning
the DEVELOPMENT of tornadoes are interest
ing. He says:
"Tornadoes always occur to the south of
the storm center and almost always a little
east of the general cyclonic storm. The
center of the storm is lightest and the air
flows in all directions toward it, but owing
to the effect of the earth's rotation these
currents are detected to the. right as they
move toward the storm center The air
from the south and east is moving from
the south and is warm and moist, both of
which conditions tend to make it light.
The air behind or TO the west side of the
storm is moving from the northwest. 1t
is much colder and consequently denser.
The whole storm is moving in an easterly
direction, but the center or axis of the
storm about which the air is flowing i'll all
directions drags behind, near the surface,
thus causing the axis of the storm to lean
toward the east. Consequently the north
| west wind in the rear of the storm, at
considerable elevation above the ground,
overlaps the south wind near the surface.
Thus a colder, denser mass OF air
flows over the lighter air underneath
and forms condition of unsta-
BILE equilibrium. The lighter air Is
pressing upward to escape, but is confined
under the mass of cold air above which is
continually increasing. Ultimately the
pressure of the warm air underneath
breaks through above, and in the rush of
the escaping current a rotary motion is
impaired. The light air charged with
moisture comes suddenly in contact with
| the dense, cold air and condensation of
the moisture ensues Immediately. This
may account for the deluge which accom-
panles the tornado"
Mr.. Hammond believes that the hail
| and rain and general friction OF the air
currents produce the electricity.
| The barometic variations during tor
nado hsve not been closely studied as the
observers are not thinking of making OBJ
servation IN the midst of the roar and
swirl of the storm. 1t is said that a good
barometic trace of the center of a storm
has never been taken on land. The best
ever obtained by the United States Signal
Service was at the Little Rock tornado.
| There the barometer registered sudden
fall of half-inch. The depression was
very great and rapid.
In scientific parlance hurricane and
cyclone are the same. One cyclone eX-
tending over great area of country may
create as many as fifty tornadoes. The
| funnel-shaped cloud, or what appears to
the vision as cloud resembling great
funnel, is not so shaped. The condensa-
tion of moisture above gives the cloud
this rese blance, but as matter of fact
the swirl is no larger at the top than at
the bottom.
Before the later dispatches were received,
| giving the exact movement of the tornado
which swept over st. Louis. Mr.. Harmon
| outlined its course, and the subsequent
accounts by wire verified the correctness
of his outlining. He traced the streets
and avenues running from the river
! Lafayette, Chateau, Poplar, Clark, Elm,
Market, Chestnut, Pine. Olive Locust and
| Washington. He traced also the streets
running north and south, or following in
some degree the course of the Mississippi
River, to wit: Main, Broadway and the
numbered streets to Twenty-sixth, Jeffer-
! son avenue, the numbered streets again to
| Thlrty-ninth street and Grand avenue,
out to Kings Highway and Fifty-second
! street. He pointed out the wharf : boat
stations below the Eads bridge, where the
steamers OF the Jo Diamond line land,
and where the excursion-boats lay, and
| figured correctly that the tornado came
! from the southwest.
! In st. Louis, Market street running
! from the river west is the central thorough
| fare, from which streets running at right
angles begin numbering. The storm, it
| appears, wrought the greatest destruction
! south of Market, and must have swept
down the valley of Mill Greek from the
southwest. The damage caused north of
that street, at the racetrack and other
places, was probably done by the fierce
northwest wind which preceded the tor
nado from the southwest. The accounts
by wire from st. Louis distinctly refer to
an east wind which blew for short time,
then the lull, followed by roaring blast
from the northwest. After this veering of
the elements there was short season of
calm before the great tornado came from
the southwest IL all its force and fury.
Mr.. Harmon contends that the tor
nado which crossed the Mississippi River
In PlKe OOQntF was WnOliy 1nuepenQenL
of the storm which struck st. Louis. He
also inclines to the opinion that the tor
nado at Evansville, Ind, was local tor
nado generated by atmospheric conditions,
which then extended throughout the cy-
clonic area
tornado soon loses its force after the
warm, light air near the surface of the
ground escapes. The temperature then
falls and the winds subside. 1t is well
known to all persons who have lived for
years in the Middle West the region COM
monty known as the Mississippi Valley
that the tornadoes or so-called cyclones
are preceded by close. warm, sultry day.
The lower strata of air becomes warm as
the day advances, hence it is quite COM
mon tor the elements to be, at the close of
the day, in a condition favorable to an
explosion.
The theory of United States signal OBJ
servers that the electricity is produced by
rain and hail is not borne out by indie
pendent observation. Often in the West
one will observe the flashes of lightning
hafn a1n fArp ad int