The Barre daily times. (Barre, Vt.) 1897-1959, 1912-10-14
RIVERS IN The AIR
Curious Play Of the Winds In the
Yosemite Valley.
EBB AND FLOW WITH THE SUN

! tnese AIT Sufrents OF rT ans 'N'S w
Regular That They May Almost 81
Timed-Mirror Lake and the Srsay
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 leau.
ty? In the famed Yosemite valley the
most interesting feature is. TO the sci
enlist perhaps, its winds.
The winds there are seldom more
than light zephyrs. moody and capri.
cious to the ordinary tourist, but when
rightly understood one of the wonders
of the valley. These interesting facts
are told by Professor r. E. Matthes 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.
lite valley, he says. In the first place,
the sun naturally heats the ground
more rapidly than 1t does the air.
Thus every hillside basking In the sun
becomes O heat radiator and gradually
warns the air above 1t. so that the air,
becoming lighter. begins TO rise.
But under these conditions the ali
does not rise vertically because the ale
directly over 1t is still cool and is press.
ing downward Therefore up the sides
80 rIa ha hnp Tod q - n i
its way. That is why the tourist max.
Ing his way up the mountain slope
with the sun on his back finds his own
dust travelling upward with him In
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
it's 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 a 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 1t 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 slope
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 go.
Glacier Point is one place in pnrticu.
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. As
the afternoon wears on and the shad-
Dws in the valley gather the cold draft
In the hills pours downward. forming
the valley like great river and flow
ing on TO the plains below. Every side
,anyon and valley sends its re-enforce
nents. like the tributaries Of great
liver. to this general air current fiow
ng onward 10 the pain.
With the return OF the morning SUP
he earth at the tops of the hills IL
warmed and the downward current In
he air is suspended. The up draft soon l
,egins as the sun shines into the val. !
eys. The air currents are 81 regula |
hat they may almost be timed.
Few realize. says the author of the
,aper. that It is on these reversing air {
urrents that one of the chief attrac- s
ions OF the Yosemite depends. Mir
or lake. to be viewed at its best. must
e seen in the early dawn. when the
elections are most perfect.
The lake is stillest and its surface
lost mirror-lilse when the cold night b
urrents have ceased and the uprising
az currents Of air have not yet be a
un. Yet unless one is punctual b =
Ill miss the chief beauty OF the place,
lr this perfect stiffness is as brief as
De turn Of the tide.
In the evening aud during the night, 2,
hen the down draft Of air from the .,
ountain sides Is strong. the stream "a
cool air pressing down the slope
unges -oTer cliffs. inst as water Ia n