The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1912-06-03
RIVERS IN The AIR
Curious Play Of the Winds In the
Yosemite Valley.
EBB AND FLOW WITH THE SUN

These Air Currents or Air Fails Are So
Regular That They May Almost Be
Timed--Mirror Lake and the Spray
Combs at Bridal Veil Falls.
Did you know there are air falls IN
the atmosphere just as real and ap
parent as are the waterfalls you have
so often viewed with admiration and
delight because Of their natural beau
ty? In the famed Yosemite valley the
most interesting feature is, to the sci
entls perhaps, its winds
The winds there are seldom more
than light zephyrs moody and caprl
cious to the ordinary tourist but when
rightly understood one Of the wonders
of the valley These interesting facts
are told by Professor +. l. Matlhes Of
the United States geological survey in
the Sierra Club Bulletin.
In no other place in the entire world
| perhaps are the air currents more sys-
tematic and regular than in the Yosem.
tie valley. he says. In the first place.
the sun naturally heats the ground
more rapidly than it does the air
Thus every hillside basking in the sun
becomes heat radiator and gradually
warns the air above It, so that the air
becoming lighter, begins to rise.
But under these conditions the air
does not rise vertically because the air
directly over it is still cool and is press
ing downward. Therefore up the sides
Of the warm slope the heated air makes
its way That is why the tourist max
ing his way up the mountain slope
with the sun on his back finds bis own
dust travelling upward with him in a
choking cloud.
But on coming down the same trail.
when the face Of the slope is in the
shadow. the dust ever descends with
the traveller in the same irritating
cloud When the face Of the mountain
is in the shade the air is cooling from
the face OF the slope and is pressing
its way down into the valley
Just as soon as the sun leaves the
slope OF the mountain the earth be-
gins to lose its heat by radiation and
in very short time IS really cooler
than the air. The layer OF air next
the face OF the hillside chills by con
tact with the earth and. becoming
heavier as it condenses. begins TO press
down along the slope Thus there are
normally the warm up draft on the
sunny slope and the cold down draft
on the side in the shadow In wind
less region like the Yosemite this rule
may be depended upon at almost any
time
But in the Yosemite. with its bold
cliff topography. these upward and
downward air currents are somewhat
interrupted On every sunny slop,
bold cliffs create shadows and conse
quently there are downward air cur
rents or local breezes daily at regular
hours as the shadows come and 60
Glacier Point is one place In partlcu
lar IN which Professor Matthes says
this shadowy effect on the air cur
rents may readily be tested by casting
small bits Of paper into the air Al
the afternoon wears on and the shad
ows in the valley gather the cold draf
In the hills pours downward. forminl
the valley Ike great river and flow
ing on to the plains below Every sidi
canyon and valley sends It's re-enforce
ments, like the tributaries Of grca
river. to this general air current flow
ing onward TO the plain
With the return OF the morning SUI
the earth at the tops OF the bills 4
warmed and the downward current II
the air is suspended. The up draft sool
begins as the sun shines into the val
leys. The air currents are so regula
that they may almost be timed.
P Few realize. says the author OF tn
b paper. that It Is on these reversing al
currents that one Of the chief attraC
tons Of the Yosemite depends Mn
ror lake. to be viewed at its best. mus
be seen In the early dawn, when IN
. reflections are most perfect.
i The lake is stillest and its surfac
D most mirror-like when the cold nigh
currents have ceased and the uprisin
e day currents OF air have not yet b,
j gun Yet unless one is puuctual h
b will miss the chief beauty OF the plac,
for this perfect stiffness is as brief a
the turn Of the tide
In the evening aud during the nigh
when the down draft Of air from III
mountain sides is strong. the streaI
OF cool air pressing down the slor
plunges over cliffs. just as water
u seen 10 fall from similar heights o
& elther the Yosemite falls or the New.