Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1912-09-19
Rivers In
the Air

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Did you know there are air.falls In
the atmosphere Just as real and appar.
ent as are the waterfalls you have SO
often Viewed with admiration and de.
light because Of their natural beauty?
IN the famed Yosemite valley the most
interesting feature is, to the scientist
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 Prof. 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.
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 be.
comes heat radiator and gradually
warns the air above It, so that the air,
becoming lighter, begins to rise.
But under those conditions tho air
does not rise vertically because the afr
directly over It is still cool and ia
pressing downward. Therefore, up the
sides Of the warm slope the heated air
makes its way. That Is why the tour.
list making his way up the mountain
slope with the sun on his back finds
his own dust travelling upward with
him in q 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 it's 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 heav.
Ter as 1t condenses, begins to press
down along the slope. Thus there Is.
normally, the warm updraft on the
sunny slope and the cold downdraft on
the side in the shadow. In a MINDLESS
region like 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.
quentV there are downward air cur.
rents Of local breezes daily at regular
hours, as the shadows come and go.
Glacier Point is one place in partic
ular in which Professor Matthes says
this shadowy effect on the air currents
may readily be tested by casting small
ernoon wears on and the shadows in
the valley gather, the cold draft in the
hills pours downward, forming the val
ley like great river, and flowing on
to the plains below. Every side can
yon and valley sends its reinforce
ments. like the tributaries Of a great
river, to this general air current flow
Ing onward 10 tue pam.
With the return OF the morning sun,
the earth at the tops Of the hills is
warmed and the downward current in
the air is suspended. The updraft soon
begins as the sun shines into the val
leys. The air currents are so regular
that they may almost be timed.
Few realize, says the author Of the
paper, that 1t IL on these reversing all
currents that one of the chief attrao
lions Of the Yosemite depends. Mirror
lake. to be viewed at It's best, must b
seen in the early dawn, when the re
Elections are most perfect
The lake is stillest and its surfac>
most mirror.like when the cold night
currents have ceased and the uprising
day currents Of air have not yet be
gun. Yet unless one is punctual h
will miss the chief beauty Of the place
for this perfect stiffness is as brief Al
the turn Of the tide.
In the evening and during the night
when the downdraft OF air from thu
mountain sides is strong, the stream o.
cool air pressing down the slope plum
ges over cliffs Just as water Is seer
to fall from similar heights. On either
the Yosemite falls or the Nevada fall
trails. this air-fall curiosity is readil!
encountered In the evening.
During the daytime. on the othel
hand, the air rises vertically along thu
cliffs and up into the hanging valleys
taking part of the spray from the fall
along with 1t. A pretty example OF thu
air carrying the spray from the fall
upward may be seen at Bridal Vel
falls. where two little combs OF spray
one on each side Of the stream. stead
lily curve upward over the brink.
AS soon as tho sun is of the cliA
the spray combs cease to exist.