LIGHT, AIR, AND COLOR
[Sidenote: Popular ideas of the desert.]
These deserts, cut through from north to south by a silent river and
from east to west by two noisy railways, seem remarkable for only a few
commonplace things, according to the consensus of public opinion. All
that one hears or reads about them is that they are very hot, that the
sunlight is very glaring, and that there is a sand-storm, a thirst, and
death waiting for every traveller who ventures over the first divide.
[Sidenote: Sunlight on desert.]
[Sidenote: Glare and heat.]
There is truth enough, to be sure, in the heat and glare part of it,
and an exceptional truth in the other part of it. It is intensely hot
on the desert at times, but the sun is not responsible for it precisely
in the manner alleged. The heat that one feels is not direct sunlight
so much as radiation from the receptive sands; and the glare is due
not to preternatural brightness in the sunbeam, but to there being no
reliefs for the eye in shadows, in dark colors, in heavy foliage.
The vegetation of the desert is so slight that practically the whole
surface of the sand acts as a reflector; and it is this, rather than
the sun’s intensity, that causes the great body of light. The white
roads in Southern France, for the surface they cover, are more glaring
than any desert sands; and the sunlight upon snow in Minnesota or New
England is more dazzling. In certain spots where there are salt or
soda beds the combination of heat and light is bewildering enough for
anyone; but such places are rare. White is something seldom seen on
desert lands, and black is an unknown quantity in my observations. Even
lava, which is popularly supposed to be as black as coal, has a reddish
hue about it. Everything has some color--even the air. Indeed, we shall
not comprehend the desert light without a momentary study of this
desert air.
[Sidenote: Pure sunlight.]
[Sidenote: Atmospheric envelope.]
The circumambient medium which we call the atmosphere is to the earth
only as so much ground-glass globe to a lamp--something that breaks,
checks, and diffuses the light. We have never known, never shall
know, direct sunlight--that is, sunlight in its purity undisturbed by
atmospheric conditions. It is a blue shaft falling perfectly straight,
not a diffused white or yellow light; and probably the life of the
earth would not endure for an hour if submitted to its unchecked
intensity. The white or yellow light, known to us as sunlight, is
produced by the ground-glass globe of air, and it follows readily
enough that its intensity is absolutely dependent upon the density
of the atmosphere--the thickness of the globe. The cause for the
thickening of the aërial envelope lies in the particles of dust, soot,
smoke, salt, and vapor which are found floating in larger or smaller
proportions in all atmospheres.
[Sidenote: Vapor particles.]
[Sidenote: Clear air.]
In rainy countries like England and Holland the vapor particles alone
are sufficiently numerous to cause at times great obscurity of light,
as in the case of fog; and the air is only comparatively clear even
when the skies are all blue. The light is almost always whitish, and
the horizons often milky white. The air is thick, for you cannot see
a mountain fifteen miles away in any sharpness of detail. There is a
mistiness about the rock masses and a vagueness about the outline. An
opera-glass does not help your vision. The obscurity is not in the eyes
but in the atmospheric veil through which you are striving to see.
On the contrary, in the high plateau country of Wyoming, where the
quantities of dust and vapor in the air are comparatively small, the
distances that one can see are enormous. A mountain seventy miles away
often appears sharp-cut against the sky, and at sunset the lights and
shadows upon its sides look only ten miles distant.
[Sidenote: Dust particles.]
[Sidenote: Hazes.]
But desert air is not quite like the plateau air of Wyoming, though one
can see through it for many leagues. It is not thickened by moisture
particles, for its humidity is almost nothing; but the dust particles,
carried upward by radiation and the winds, answer a similar purpose.
They parry the sunshaft, break and color the light, increase the
density of the envelope. Dust is always present in the desert air in
some degree, and when it is at its maximum with the heat and winds of
July, we see the air as a blue, yellow, or pink haze. This haze is not
seen so well at noonday as at evening when the sun’s rays are streaming
through canyons, or at dawn when it lies in the mountain shadows and
reflects the blue sky. Nor does it muffle or obscure so much as the
moisture-laden mists of Holland, but it thickens the air perceptibly
and decreases in measure the intensity of the light.
[Sidenote: Seeing the desert air.]
[Sidenote: Sea breezes on desert.]
Yet despite the fact that desert air is dust-laden and must be
thickened somewhat, there is something almost inexplicable about
it. It seems so thin, so rarefied; and it is so scentless--I had
almost said breathless--that it is like no air at all. You breathe it
without feeling it, you look through it without being conscious of
its presence. Yet here comes in the contradiction. Desert air is very
easily recognized by the eyes alone. The traveller in California when
he wakes in the morning and glances out of the car-window at the air in
the mountain canyons, knows instantly on which side of the Tehachepi
Range the train is moving. He knows he is crossing the Mojave. The
lilac-blue veiling that hangs about those mountains is as recognizable
as the sea air of the Massachusetts shore. And, strange enough, the sea
breezes that blow across the deserts all down the Pacific coast have no
appreciable effect upon this air. The peninsula of Lower California is
practically surrounded by water, but through its entire length and down
the shores of Sonora to Mazatlan, there is nothing but that clear, dry
air.
[Sidenote: Colored air.]
[Sidenote: Different hues.]
I use the word “clear” because one can see so far through this
atmosphere, and yet it is not clear or we should not see it so plainly.
There is the contradiction again. Is it perhaps the coloring of it
that makes it so apparent? Probably. Even the clearest atmosphere has
some coloring about it. Usually it is an indefinable blue. Air-blue
means the most delicate of all colors--something not of surface depth
but of transparency, builded up by superimposed strata of air many
miles perhaps in thickness. This air-blue is seen at its best in the
gorges of the Alps, and in the mountain distances of Scotland; but it
is not so apparent on the desert. The coloring of the atmosphere on the
Colorado and the Mojave is oftener pink, yellow, lilac, rose-color,
sometimes fire-red. And to understand that we must take up the
ground-glass globe again.
[Sidenote: Producing color.]
[Sidenote: Refracted rays.]
It has been said that our atmosphere breaks, checks, and diffuses the
falling sunlight like the globe of a lamp. It does something more. It
acts as a prism and breaks the beam of sunlight into the colors of
the spectrum. Some of these colors it deals with more harshly than
others because of their shortness and their weakness. The blue rays,
for instance, are the greatest in number; but they are the shortest
in length, the weakest in travelling power of any of them. Because of
their weakness, and because of their affinity (as regards size) with
the small dust particles of the higher air region, great quantities of
these rays are caught, refracted, and practically held in check in the
upper strata of the atmosphere. We see them massed together overhead
and call them the “blue sky.” After many millions of these blue rays
have been eliminated from the sunlight the remaining rays come down to
earth as a white or yellow or at times reddish light, dependent upon
the density of the lower atmosphere.
[Sidenote: Cold colors, how produced.]
[Sidenote: Warm colors.]
Now it seems that an atmosphere laden with moisture particles obstructs
the passage earthward of the blue rays, less perhaps than an atmosphere
laden with dust. In consequence, when they are thus allowed to come
down into the lower atmosphere in company with the other rays, their
vast number serves to dominate the others, and to produce a cool tone
of color over all. So it is that in moist countries like Scotland you
will find the sky cold-blue and the air tinged gray, pale-blue, or
at twilight in the mountain valleys, a chilly purple. A dust-laden
atmosphere seems to act just the reverse of this. It obstructs all the
rays in proportion to its density, but it stops the blue rays first,
holds them in the upper air, while the stronger rays of red and yellow
are only checked in the lower and thicker air-strata near the earth.
The result of this is to produce a warm tone of color over all. So it
is that in dry countries like Spain and Morocco or on the deserts of
Africa and America, you will find the sky rose-hued or yellow, and the
air lilac, pink, red, or yellow.
[Sidenote: Sky colors.]
I mean now that the air itself is colored. Of course countless
quantities of light-beams and dispersed rays break through the aërial
envelope and reach the earth, else we should not see color in the
trees or grasses or flowers about us; but I am not now speaking of the
color of objects on the earth, but of the color of the air. A thing
too intangible for color you think? But what of the sky overhead? It
is only tinted atmosphere. And what of the bright-hued horizon skies
at sunrise and sunset, the rosy-yellow skies of Indian summer! They
are only tinted atmospheres again. Banked up in great masses, and seen
at long distances, the air-color becomes palpably apparent. Why then
should it not be present in shorter distances, in mountain canyons,
across mesas and lomas, and over the stretches of the desert plains?
[Sidenote: Color produced by dust.]
[Sidenote: Effect of heat.]
The truth is all air is colored, and that of the desert is deeper dyed
and warmer hued than any other for the reasons just given. It takes
on many tints at different times, dependent upon the thickening of
the envelope by heat and dust-diffusing winds. I do not know if it is
possible for fine dust to radiate with heat alone; but certain it is
that, without the aid of the wind, there is more dust in the air on hot
days than at any other time. When the thermometer rises above 100° F.,
the atmosphere is heavy with it, and the lower strata are dancing and
trembling with phantoms of the mirage at every point of the compass. It
would seem as though the rising heat took up with it countless small
dust-particles and that these were responsible for the rosy or golden
quality of the air-coloring.
[Sidenote: Effect of winds.]
[Sidenote: Sand-storms.]
There is a more positive tinting of the air produced sometimes by high
winds. The lighter particles of sand are always being drifted here and
there through the aërial regions, and even on still days the whirlwinds
are eddying and circling, lifting long columns of dust skyward and
then allowing the dust to settle back to earth through the atmosphere.
The stronger the wind, and the more of dust and sand, the brighter
the coloring. The climax is reached in the dramatic sand-storm--a
veritable sand-fog which often turns half the heavens into a luminous
red, and makes the sun look like a round ball of fire.
[Sidenote: Reflections upon sky.]
[Sidenote: Blue, yellow, and pink hazes.]
The dust-particle in itself is sufficient to account for the warmth
of coloring in the desert air--sufficient in itself to produce the
pink, yellow, and lilac hazes. And yet I am tempted to suggest some
other causes. It is not easy to prove that a reflection may be thrown
upward upon the air by the yellow face of the desert beneath it--a
reflection similar to that produced by a fire upon a night sky--yet I
believe there is something of the desert’s air-coloring derived from
that source. Nor is it easy to prove that a reflection is cast by blue,
pink, and yellow skies, upon the lower air-strata, yet certain effects
shown in the mirage (the water illusion, for instance, which seems only
the reflection of the sky from heated air) seem to suggest it. And
if we put together other casual observations they will make argument
toward the same goal. For instance, the common blue haze that we may
see any day in the mountains, is always deepest in the early morning
when the blue sky over it is deepest. At noon when the sky turns
gray-blue the haze turns gray-blue also. The yellow haze of the desert
is seen at its best when there is a yellow sunset, and the pink haze
when there is a red sunset, indicating that at least the sky has some
part in coloring by reflection the lower layers of desert air.
[Sidenote: The dust-veil.]
[Sidenote: Summer coloring.]
Whatever the cause, there can be no doubt about the effect. The desert
air is practically colored air. Several times from high mountains I
have seen it lying below me like an enormous tinted cloud or veil.
A similar veiling of pink, lilac, or pale yellow is to be seen in
the gorges of the Grand Canyon; it stretches across the Providence
Mountains at noonday and is to be seen about the peaks and packed in
the valleys at sunset; it is dense down in the Coahuila Basin; it is
denser from range to range across the hollow of Death Valley; and it
tinges the whole face of the Painted Desert in Arizona. In its milder
manifestations it is always present, and during the summer months its
appearance is often startling. By that I do not mean that one looks
through it as through a highly colored glass. The impression should not
be gained that this air is so rose-colored or saffron-hued that one
has to rub his eyes and wonder if he is awake. The average unobservant
traveller looks through it and thinks it not different from any
other air. But it is different. In itself, and in its effect upon the
landscape, it is perhaps responsible for the greater part of what
everyone calls “the wonderful color” of the desert.
[Sidenote: Local hues.]
[Sidenote: Greens of desert plants.]
And this not to the obliteration of local hue in sands, rocks, and
plants. Quite independent of atmospheres, the porphyry mountains are
dull red, the grease wood is dull green, the vast stretches of sand are
dull yellow. And these large bodies of local color have their influence
in the total sum-up. Slight as is the vegetation upon the desert, it is
surprising how it seems to bunch together and count as a color-mass.
Almost all the growths are “evergreen.” The shrubs and the trees shed
their leaves, to be sure, but they do it so slowly that the new ones
are on before the old ones are off. The general appearance is always
green, but not a bright hue, except after prolonged rains. Usually
it is an olive, bordering upon yellow. One can hardly estimate what
a relieving note this thin thatch of color is, or how monotonous the
desert might be without it. It is welcome, for it belongs to the scene,
and fits in the color-scheme of the landscape as perfectly as the
dark-green pines in the mountain scenery of Norway.
[Sidenote: Color of sands.]
[Sidenote: Sands in mirage.]
The sands, again, form vast fields of local color, and, indeed, the
beds of sand and gravel, the dunes, the ridges, and the mesas, make
up the most widespread local hue on the desert. The sands are not
“golden,” except under peculiar circumstances, such as when they are
whirled high in the air by the winds, and then struck broadside by the
sunlight. Lying quietly upon the earth they are usually a dull yellow.
In the morning light they are often gray, at noon frequently a bleached
yellow, and at sunset occasionally pink or saffron-hued. Wavering heat
and mirage give them temporary coloring at times that is beautifully
unreal. They then appear to undulate slightly like the smooth surface
of a summer sea at sunset; and the colors shift and travel with the
undulations. The appearance is not common; perfect calm, a flat plain,
and intense heat being apparently the conditions necessary to its
existence.
[Sidenote: Color of mountain walls.]
[Sidenote: Weather staining.]
The rocks of the upper peaks and those that make the upright walls of
mountains, though small in body of color, are perhaps more varied in
hue than either the sands or the vegetation, and that, too, without
primary notes as in the Grand Canyon of the Yellowstone. The reds
are always salmon-colored, terra-cotta, or Indian red; the greens are
olive-hued, plum-colored, sage-green; the yellows are as pallid as
the leaves of yellow roses. Fresh breaks in the wall of rock may show
brighter colors that have not yet been weather-worn, or they may reveal
the oxidation of various minerals. Often long strata and beds, and
even whole mountain tops show blue and green with copper, or orange
with iron, or purple with slates, or white with quartz. But the tones
soon become subdued. A mountain wall may be dark red within, but it is
weather-stained and lichen-covered without; long-reaching shafts of
granite that loom upward from a peak may be yellow at heart but they
are silver-gray on the surface. The colors have undergone years of
“toning down” until they blend and run together like the faded tints of
an Eastern rug.
[Sidenote: Influence of the air.]
[Sidenote: Peak of Baboquivari.]
But granted the quantity and the quality of local colors in the desert,
and the fact still remains that the air is the medium that influences
if it does not radically change them all. The local hue of a sierra may
be gray, dark red, iron-hued, or lead-colored; but at a distance, seen
through dust-laden air, it may appear topaz-yellow, sapphire-blue,
bright lilac, rose-red--yes, fire-red. During the heated months of
summer such colors are not exceptional. They appear almost every
evening. I have seen at sunset, looking north from Sonora some twenty
miles, the whole tower-like shaft of Baboquivari change from blue to
topaz and from topaz to glowing red in the course of half an hour. I do
not mean edgings or rims or spots of these colors upon the peak, but
the whole upper half of the mountain completely changed by them. The
red color gave the peak the appearance of hot iron, and when it finally
died out the dark dull hue that came after was like that of a clouded
garnet.
[Sidenote: Buttes and spires.]
[Sidenote: Sun-shafts through canyons.]
The high ranges along the western side of Arizona, and the buttes and
tall spires in the Upper Basin region, all show these warm fire-colors
under heat and sunset light, and often in the full of noon. The colored
air in conjunction with light is always responsible for the hues. Even
when you are close up to the mountains you can see the effect of the
air in small ways. There are edgings of bright color to the hill-ridges
and the peaks; and in the canyons, where perhaps a sunshaft streams
across the shadow, you can see the gold or fire-color of the air most
distinctly. Very beautiful are these golden sun-shafts shot through
the canyons. And the red shafts are often startling. It would seem as
though the canyons were packed thick with yellow or red haze. And so in
reality they are.
[Sidenote: Complementary hues in shadow.]
There is one marked departure from the uniform warm colors of the
desert that should be mentioned just here. It is the clear blue seen
in the shadows of western-lying mountains at sunset. This colored
shadow shows only when there is a yellow or orange hued sunset, and
it is produced by the yellow of the sky casting its complementary hue
(blue) in the shadow. At sea a ship crossing a yellow sunset will show
a marvellous blue in her sails just as she crosses the line of the sun,
and the desert mountains repeat the same complementary color with equal
facility and greater variety. It is not of long duration. It changes as
the sky changes, but maintains always the complementary hue.
[Sidenote: Colored shadows.]
[Sidenote: Blue shadows upon salt-beds.]
The presence of the complementary color in the shadow is exceptional,
however. The shadows cast by such objects as the sahuaro and the palo
verde are apparently quite colorless; and so, too, are the shadows of
passing clouds. The colored shadow is produced by reflection from
the sky, mixed with something of local color in the background, and
also complementary color. It is usually blue or lilac-blue, on snow
for example, when there is a blue sky overhead; and lilac when shown
upon sand or a blue stone road. Perhaps it does not appear often on
the Mojave-Colorado because the surfaces are too rough and broken with
coarse gravel to make good reflectors of the sky. The fault is not in
the light or in the sky, for upon the fine sands of the dunes, and upon
beds of fine gypsum and salt, you can see your own shadow colored an
absolute indigo; and often upon bowlders of white quartz the shadows of
cholla and grease wood are cast in almost cobalt hues.
[Sidenote: How light makes color.]
[Sidenote: Desert sunsets.]
All color--local, reflected, translucent, complementary--is, of course,
made possible by light and has no existence apart from it. Through
the long desert day the sunbeams are weaving skeins of color across
the sands, along the sides of the canyons, and about the tops of the
mountains. They stain the ledges of copper with turquoise, they burn
the buttes to a terra-cotta red, they paint the sands with rose and
violet, and they key the air to the hue of the opal. The reek of color
that splashes the western sky at sunset is but the climax of the sun’s
endeavor. If there are clouds stretched across the west the ending is
usually one of exceptional brilliancy. The reds are all scarlet, the
yellows are like burnished brass, the oranges like shining gold.
But the sky and clouds of the desert are of such unique splendor that
they call for a chapter of their own.