The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1908-02-23


the breeding place of the greatest and
most destructive ones. l. The air must
be calm to begin with; for were ii in
motion no part of it could remain long
enough close to the ground to be great
ly warmed. g The surface must be
fiat; for were it sloping. the lower air
would flow up the slopes as fast as it
became a little heated. 3. The surface
must be dry; for were il wet, much OF
the suns heat would be occupied in
evaporating the water, and thus lost
TO the lower air. f. The surface must
be barren; for were it covered with
vegetation, it could not get so highly
heated Only on the desert, therefore,
can the sun readily warm the surface
air to such excess that the lower layer
may be compared to a film of oil bal
aliced beneath layer of water. As
little disturbance would cause the two
liquids to change places, so with the
very unstable equilibrium of the hot air
on the desert, there is a strong up
draught when the upsetting comes. As
the hot air rushes up, the surrounding
air flows in, dust and sand being
blown to the center and rising with
the ascending current. AS the air meets
In the center, rotary motion is es-
tablshed, and the disturbance becomes
a whirlwind. Forty feet from the CEN
ter there may be only a breeze; but
at the center the whirling motion may
become so strong that a partial vacuum
results, and objects are shot into the
center as if from a gun. In small
whirlWinds the direction of the Whirl-
ing may be indifferently one way or the
other, according to the side on which
the indraught happens to pass the CEN
ter. Such a whirlwind will stop toward
AFTERNOON, when the sun loses its power
to supply the cause for it's motion.
We often see the small whirls in the
daytime in our dry places, especially
upon the desert lands. But they never
seem TO develop into the sand spouts"
of the Sahara, or the immense dust
storms common in the far east.
The desert Whirl has a broad base
(due TO the very hot surface air-Some-
times $50 degrees-nOt more than five
feet high but does not rise far in air
because of the restricted land area that
can present a perfectly fiat surface TO
the suns rays. 1t may be tiny whirl
of dust, or a considerable dust storm;
but il usually occurs only at or near
midday, and in the afternoon it dies
away. 1t is a dry storm.
The Oceanic Cyclone.
The oceanic cyclone may cover an
CLASSY stiIl-but the surface tempera
ture seldom exceeds 50 degrees. Yet
this air being saturated, contains pO-
tentially more heat than the desert
air contains at $50 degrees. The warm
sea air may form a thick stratum of al
most indefinite height, because the in
visible vapOr of water. evaporated from
the ocean surface by the SUMS rays, is
many times lighter than dry air, and
= 70 n haf
reaches its dew point and eondenses,
which il may not reach for hundreds of
feet; and if in rising 300 feet ii does not
cool more than 1.6 degrees, the air it
self will rise as well as the vapor. But
as soon as the vapor condenses back
into clouds or rain, each pound that
does so. gives off 1000 degrees of heat,
thereby sustaining the warmth lost by
rising. These storms are thus self
feeders, and may last long time.
The Calm Before the Storm.
The greater storms that originate
within the tropics but not in desert re-
gions are nearly always accompanied
by rain There is good reason for
thinking that these cyclones generally
spring up in the zone of Gains, much
as the desert whirls begin; for they
seem never to begin in places of well
established wind currents, but rather
in a place of quiet weak, or variable
winds 1t is only during times of stag
nation when the air has no established
motion, but stands about idly as il
waiting for a command to move on,
that the lower air may become very
warm and very moist, and ready for an
OvertUrning. A calm usually precedes
one q these storms at sea; the air be-
comes close and Oppressively warm;
the water settles down to a CLASSY sur
face-these being the conditions that
cause the cyclonic storm. Here the area
of disturbance is much greater than
on the desert.
The Great Storage of Heat.
There is a lower temperature of the
heated air next to the water surface
than there is next to a land surface,
but a much greater amount of heat in
this air above the water because of the
vast amounts of latent heat stored in
the eVaporated water held in suspen-
sion in the warm air; every pound of
water that evapOrates takes in 900 de-
grees of heat without any rise in the
temperature of the vapor or of the air
that holds it. That is. il takes as much
heat to pass one pound of water at 2l2
degrees into steam at 212 degrees as
would raise 1000 pounds of water one
degree say from 80 degrees to 40 de-
of the suns heat that would pass on
the desert TO the dry sand, and so the
depth of the heated air stratum over the
water is much greater than the similar
LAYER over the land. Most of the heat
reflected back from the water is like
wise caught by the moisture. which is
not nearly 50 diatherInanus (penetrable
by heat as dry air is. While, therefore.
the temperature of the heated air next
TO the desert Qess than five feet hlgh)
often rises TO 140 or $50 degrees f.
close to the ground, that over the trop-
zeal seas rarely exceeds 50 degrees.
Nevertheless, the sea air contains by far
the greater amount of heat, as just ex-
planned; for what the sea air lacks IN
sensible heat it makes up in latent heat.
and what il lacks in actual heat II
makes up in amount or depth of the
air that is warmed.
Why Motion Begins.
How the sea-cyclone begins, that IS,
what begins the upsetting of the air
strata, is not entirely known. Prob
ably one place gets a little warmer than
surrounding spaces and gentle cur