Lexington gazette. [volume] (Lexington, Va.) 1871-1962, 1912-02-28
RIVERS in The AIR
Curious Play of the Winds In the
Yosemite Valley.
EBB AND FLOW WITH THE SUN
These Air Currents or Air Falls 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
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 F. 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-
tie valley. he says In the first place.
the sun naturally heats the ground
more rapidly than it does the air
Thus every hillside baskiRg in the sun
becomes q heat radiator and gradually
warns the air above it. so that the air,
becoming lighter. begins to rise.
But under these conditions 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 his 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 q 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 a 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 so.
Glacier Point Is one place in particu-
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-
ows in the valley gather the cold draft
in the hills pours downward. forming
the valley like 4 great river and flow
ing on to the plains below Every side
canyon and valley sends its re-enfOrce
ments. like the tributaries OF great
river. TO this general air current flow
ing onward 10 the plain.
With the return OF the morning SUI
the earth at the tops OF the hills i.
]
the air is suspended. The up draft @ooI
begins as the sun shines into the val
, legs The air currents are so regular
, that they may almost be timed.
Few realize. says the author of tn,
paper. thar il is ON these reversing al
currents that one of the chief attrac
-, tons of the Yosemite depends. Mir
:, ror lake. TO be viewed at its best. mus
. be seen in the early dawn. when tn
2 reflections are most perfect
The lake is stileSt and its surfac
= most mirrOr-like when the cold nigh
= currents have ceased and the uprisin
: day currents OF air have not yet be
gun. Yet unless one is punctual 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 and during the nigh
when the down draft of air from tn
mountain sides is strong. the streai
of cool air pressing down the sloT
plunges over cliffs. just as water
~ seen to fall from similar heights. o
either the Yosemite falls or the New
da falls trails this air fall curiosity
= readily encountered in the evening.
During the daytime. on the oth'
hand. the mir rises vertically along II
cliffs and mp into the hanging valley
taking part of the spray from the fal
. along with it, \ pretty example
II the air carrying the spray from II
fall upward may be seen at Bird
Veil falls. where two little combs
spray. one on each side of the streaI
steadily curve upward over the brin
AS soon as the sun is of the eli