CHAPTER VIIILLUSIONS

Reality and appearance.In our studies of landscape we are very frequently made the victims of either illusion or delusion. The eye or the mind deceives us, and sometimes the two may join forces to our complete confusion. We are not willing to admit different reports of an appearance. The Anglo-Saxon in us insists that there can be only one truth, and everything else must be error. It is known, for instance, that Castle Dome, which looks down on the Colorado River from Western Arizona, is a turret of granite—gray, red, brown, rock-colored, whatever color you please. With that antecedent knowledge in mind how difficult it is for us to believe the report of our eyes which says that at sunset the dome is amethystine, golden, crimson, or perhaps lively purple. The reality is one thing, the appearance quite another thing; but why are not both of them truthful?Preconceived impressions.And how very shy people are about acceptinga pink air, a blue shadow, or a field of yellow grass—sunlit lemon-yellow grass! They have been brought up from youth to believe that air is colorless, that shadows are brown or gray or sooty black, and that grass is green—bottle-green. The preconceived impression of the mind refuses to make room for the actual impression of the eyes, and in consequence we are misled and deluded.Deception by sunlight.But do the eyes themselves always report the truth? Yes; the truth of appearances, but as regards the reality they may deceive you quite as completely as the mind deceives you about the apparent. And for the deception of the eyes there is no wizard’s cell or magician’s cabinet so admirably fitted for jugglery as this bare desert under sunlight. Its combination of light and air seem like reflecting mirrors that forever throw the misshapen image in unexpected places, in unexpected lights and colors.Distorted forms and colors.Changed appearance of mountains.What, for instance, could be more perplexing than the odd distortions in the forms and colors of the desert mountains! A range of these mountains may often look abnormally grand, even majestic in the early morning as they stand against the eastern sky. The outlines of the ridges and peaks may be clear cut, the lightand shade of the canyons and barrancas well marked, the cool morning colors of the face-walls and foot-hills distinctly placed and holding their proper value in the scene. But by noon the whole range has apparently lost its lines and shrunken in size. Under the beating rays of the sun and surrounded by wavering heated atmosphere its shadow masses have been grayed down, neutralized, perhaps totally obliterated; and the long mountain surface appears as flat as a garden wall, as smooth as a row of sand-dunes. There is no indication of barranca or canyon. The air has a blue-steel glow that muffles light and completely wrecks color. Seen through it the escarpments show only dull blue and gray. All the reds, yellows, and pinks of the rocks are gone; the surfaces wear a burnt-out aspect as though fire had eaten into them and left behind only a comb of volcanic ash.Changes in line, light, and color.At evening, however, the range seems to return to its majesty and magnitude. The peaks reach up, the bases broaden, the walls break into gashes, the ridges harden into profiles. The sun is westering, and the light falling more obliquely seems to bring out the shadows in the canyons and barrancas. Last of all thecolors come slowly back to their normal condition, as the flush of life to one recovering from a trance. One by one they begin to glow on chasm, wall, and needled summit. The air, too, changes from steel-blue to yellow, from yellow to pink, from pink to lilac, until at last with the sun on the rim of the earth, the mountains, the air, the clouds, and the sky are all glowing with the tints of ruby, topaz, rose-diamond—hues of splendor, of grandeur, of glory.Suppose, if you please, a similar range of mountains thirty miles away on the desert. Even at long distance it shows an imposing bulk against the sky, and you think if you were close to it, wall and peak would loom colossal. How surprised you are then as you ride toward it, hour after hour, to find that it does not seem to grow in size. When you reach the foot-hills the high mountains seem little larger than when seen at a distance. You are further surprised that what appeared like a flat-faced range with its bases touching an imaginary curb-stone for miles, is in reality a group-range with retiring mountains on either side that lead off on acute angles. The group is round, and has as much breadth as length. And still greater is your surprise when you discover that the green topof the gray-based mountain, which has been puzzling you for so many hours, does not belong to the gray base at all. It is a pine-clad top resting upon another and more massive base far back in the group. It is the highest and most central peak of the range.False perspective.Abnormal foreshortening.Contradictions and denials.Such illusions are common, easily explained; and yet, after all, not so easily understood. They are caused by false perspective, which in turn is caused by light and air. On the desert, perspective is always erratic. Bodies fail to detach themselves one from another, foreshortening is abnormal, the planes of landscape are flattened out of shape or telescoped, objects are huddled together or superimposed one upon another. The disturbance in aërial perspective is just as bad. Colors, lights, and shadows fall into contradictions and denials, they shirk and bear false witness, and confuse the judgment of the most experienced.Deceptive distances.No wonder amid this distortion of the natural, this wreck of perspective, that distance is such a proverbially unknown quantity. It is the one thing the desert dweller speaks about with caution. It may be thirty or fifty miles to that picacho—he is afraid to hazard a guess. If you should go up to the top of your mountain rangeand look at the valley beyond it, the distance across might seem very slight. You can easily see to where another mountain range begins and trails away into the distance. Perhaps you fancy a few hours’ ride will take you over that valley-plain to where the distant foot-hills are lying soft and warm at the bases of the mountains. You may be right and then again you may be wrong. You may spend two days getting to those foot-hills.Dangers of the desert.Immensity of valley-plains.This deception of distance is not infrequently accompanied by fatal consequences. The inexperienced traveller thinks the distance short, he can easily get over the ground in a few hours. But how the long leagues drag out, spin out, reach out! The day is gone and he is not there, the slight supply of water is gone and he is not there, his horse is gone and he himself is going, but he is not there. The story and its ending are familiar to those who live near the desert, for every year some mining or exploring party is lost. If there are any survivors they usually make the one report: “The distance seemed so short.” But there are no short distances on the desert. Every valley-plain is an immense wilderness of space.Shadow illusions.Color-patches on mountains.There is another illusion—a harmless one—thathas not to do with perspective but with shadow and local color. The appearance is that of shadows cast down along the mountain’s side by the ridges or hogbacks. Any little patch of shadow is welcome on the desert, particularly upon the mountains which are always so strongly flooded with light. But this is only a counterfeit presentment. The ridges have no vegetation upon them to hold in place the soil and rocks and these are continually breaking away into land-slips. The slips or slides expose to view streaks of local color such as may be seen in veins of iron and copper, in beds of lignite or layers of slate. It is these streaks and patches of dark color that have broken away and slipped down the mountain side under the ridges that give the appearance of shadows. They have the true value in light, and are fair to look upon even though they are deception. The weather-beaten rocks of a talus under a peak may create a similar illusion, but the shadow effect loses a velvety quality which it has when seen under the ridges.Illusion of lava-beds.Appearance of cloud-shadow.The illusion of a cloud-shadow resting upon the foot-hills or in the valley, is frequently produced by the local color of lava-beds. Lava may be of almost any color, but when seen closeto view it is usually a reddish-black. At a distance, however, and as a mass, its beds have the exact value of a cloud-shadow. Any eye would be deceived by it. The great inundations of lava that have overrun the plains and oozed down the foot-hills and around the lomas (particularly on the Mojave) look the shadow to the very life. The beds are usually hedged about on all sides by banks of fine sand that seem to stand for sunlight surrounding the shadow, and thus the deception is materially augmented. Many times I have looked up at the sky to be sure there was no cloud there, so palpable is this lava shadow-illusion.Mirage.Definition.But perhaps the most beautiful deception known to the desert is the one oftenest seen—mirage. Everyone is more or less familiar with it, for it appears in some form wherever the air is heated, thickened, or has strata of different densities. It shows on the water, on the grass plains, over ploughed fields or gravel roads, on roadbeds of railways; but the bare desert with its strong heat-radiation is primarily its home. The cause of its appearance—or at least one of its appearances—is familiar knowledge, but it may be well to state it in dictionary terms: “An optical illusion due toexcessive bending of light-rays in traversing adjacent layers of air of widely different densities, whereby distorted, displaced, or inverted images are produced.”[5]Need of explanation.This is no doubt the true explanation of that form of mirage in which people on Sahara see caravans in the sky trailing along, upside down, like flies upon the ceiling; or on the ocean see ships hanging in the air, masts and sails downward. But the explanation is very general and is itself in some need of explanation. Perhaps then I may be pardoned for trying to illustrate the theory of mirage in my own way.Refraction of light-rays.Dense air-strata.The rays of light that come from the sun to the earth appear to travel in a straight line, but they never do. As soon as they meet with and pass into the atmospheric envelope they are bent or deflected from their original direction and reach the earth by obtuse angles or in long descending curves like a spent rifle ball. This bending of the rays is called refraction, which must not be confounded with reflection—a something quite different. Now refraction is, of course, the greatest where the atmosphere is the densest. The thicker the air the more acute the bending of the light-ray. Hence the thick layersof air lying along or a few feet above the surface of the earth on a hot day are peculiarly well-fitted to distort the light-ray, and consequently well-fitted to produce the effect of mirage. These layers of air are of varying densities. Some are thicker than others; and in this respect the atmosphere bears a resemblance to an ordinary photographic or telescopic lens. Let us use the lens illustration for a moment and perhaps it will aid comprehension of the subject.Illustration of camera lens.You know that the lens, like the air, is of varying thicknesses or densities, and you know that in the ordinary camera the rays of light, passing through the upper part of the lens, are refracted or bent toward the perpendicular so that they reach the ground-glass “finder” at the bottom; and that the rays passing through the lower part of the lens go to the top of the “finder” The result is that you have on the “finder” or the negative something reversed—things upside down. That, so far as the reversed image goes, is precisely the case in mirage. The air-layers act as a lens and bend the light-rays so that when seen in our “finder”—the eye—the bottom of a tree, for example, goes to the top and the top goes to the bottom.The bent light-ray.But there is something more to mirage than this reversed image. The eyes do not see things “in their place,” but see them hanging in the air as in the case of ships and caravans. To explain this, in the absence of a diagram, we shall have to take up another illustration. Suppose a light-ray so violently bent by the heat lying above a sidewalk that it should come to us around a street corner, and thereby we should see a man coming up a side street that lies at right angles to us. He would appear to our eyes to be coming up, not the side street, but the street we are standing in. The man, to all appearances, would not be “in his place.” We should see him where he is not.Ships at sea.Ships upside down.Now suppose again instead of the light-rays bending to right or left (as in the street-corner illustration), we consider them as bending skyward or earthward. Suppose yourself at sea and that you are looking up into the sky above the horizon. You see there a ship “out of its place,” hanging in the air in an impossible manner—something which is equivalent, or at least analogous, to looking down the street and seeing the image of the man around the corner. You are looking straight into the sky, yet seeing a ship below the verge. The light-rayscoming from the ship on the water describe an obtuse angle or curve in reaching the eye. The rays from the bottom of the ship, lying in a dense part of the air-lens, are more acutely bent than those from the masts, and hence they go to the top of the photographic plate or your field of vision, whereas the rays from the ship’s masts, being in a thinner atmosphere, are less violently bent, and thus go to the bottom of your field of vision. The result is the ship high in air above the horizon-line and upside down.Wherein the illusion.“Looming” of vessels, islands, and cities.The illusion or deception consists in this: We usually see things in flat trajectory, so to speak. Light comes to us in comparatively straight rays. The mind, therefore, has formulated a law that we see only by straight rays. In the case of mirage the light comes to us on curved, bent, or angular rays. The eyes recognize this, but the mind refuses to believe it and hence is deceived. We think we see the ship in the air by the straight ray, but in reality we see the shipon the waterby the bent ray. It is thus that ships are often seen when far below the horizon-line, and that islands in the sea below the ocean’s rim, and so far away as a hundred miles, are seen looming in the air. “Looming” is the word that describes the excessiveapparent elevation of the object in the sky and is more striking on sea than land. Captains of vessels often tell strange tales of how high in the air, ships and towns and coasts are seen. The report has even come back from Alaska of a city seen in the sky that is supposed to be the city of Bristol. In tropical countries and over warm ocean-currents there are often very acute bendings of the light-rays. Why may it not be so in colder lands with colder currents?Reversed image of mountains.Horses and cattle in mirage.The form of mirage that gives us the reversed image is seen on the desert as well as on the sea; but not frequently—at least not in my experience. There is an illusion of mountains hanging peak downward from the sky, but one may wander on the deserts for months and never see it. The reality and the phantom both appear in the view—the phantom seeming to draw up and out of the original in a distorted, cloud-like shape. It is almost always misshapen, and as it rises high in air it seems to be detached from the original by currents of air drifted in between. More familiar sights are the appearances of trees, animals, houses, wagons, all hanging in the air in enlarged and elongated shapes and, of course, reversed. I have seen horses hitched to a wagon hanginghigh up in the air with the legs of the horses twenty feet long and the wagon as large as a cabin. The stilted antelope “forty feet high and upside down” is as seldom seen in the sky as upon the earth; but desert cattle in bunches of half a dozen will sometimes walk about on the aërial ceiling in a very astonishing way.Illusion of rising buttes.Yet these, too, are infrequent appearances. Nor is the illusion of buttes rising from the plain in front of you often seen. It happens only when there are buttes at one side or the other, and, I presume, this mirage is caused by the bending of the light-rays to the right or left. It presents certainly a very beautiful effect. The buttes rise up from the ground, first one and then another, until there is a range of them that holds the appearance of reality perhaps for hours, and then gradually fades out like a stereopticon picture—the bases going first and the tops gradually melting into the sky. When seen at sunset against a yellow sky the effect is magnificent. The buttes, even in illusion, take on a wonderful blue hue (the complementary color of yellow), and they seem to drift upon the sky as upon an open sea.Other causes for mirage.Water-mirage.The lake appearance.How produced.The bending of the light-rays to either sideinstead of up or down, as following the perpendicular, may or may not be of frequent occurrence. I do not even know if the butte appearance is to be attributed to that. The opportunity to see it came to me but once, and I had not then the time to observe whether the buttes in the mirage had sides the reverse of the originals. Besides, it is certain that mirage is caused in other ways than by the bending of light-rays. The most common illusion of the desert is the water-mirage and that is caused by reflection, not refraction. Its usual appearance is that of a lake or sea of water with what looks at a distance to be small islands in it. There are those with somewhat more lively imagination than their fellows who can see cows drinking in the water, trees along the margin of the shore (palms usually), and occasionally a farm-house, a ship, or a whale. I have never seen any of these wonderful things, but the water and island part of the illusion is to be seen almost anywhere in the desert basins during hot weather. In the lower portions of the Colorado it sometimes spreads over thousands of acres, and appears not to move for hours at a stretch. At other times the wavering of the heat or the swaying of the air strata, or a change in thedensity of the air will give the appearance of waves or slight undulations on the water. In either case the illusion is quite perfect. Water lying in such a bed would reflect the exact color of the sky over it; and what the eyes really see in this desert picture is the reflection of the sky not from water but from strata of thick air.Objects in the water.This illusion of water is probably seen more perfectly in the great dry lake-beds of the desert where the ground is very flat and there is no vegetation, than elsewhere. In the old Coahuila Valley region of the Colorado the water comes up very close to you and the more you flatten the angle of reflection by flattening yourself upon the ground, the closer the water approaches. The objects in it which people imagine look like familiar things are certainly very near. And these objects—wild-fowl, bushes, tufts of swamp grass, islands, buttes—are frequently bewildering because some of them are right side up and some of them are not. Some are reversed in the air and some are quietly resting upon the ground.Confused mirage.The swimming wolf.It happens at times that the whole picture is confused by the light-rays being both reflected and refracted, and in addition that the rays from certain objects come to us in a direct line.The ducks, reeds, and tufts of grass, for instance, are only clods of dirt or sand-banked bushes which are detached at the bottom by heavy drifts of air. We see their tops right side up by looking through the air-layer or some broken portion of it. But in the same scene there may be trees upside down, and mountains seen in reflection, drawn out to stupendous proportions. In the Salton Basin one hot day in September a startled coyote very obligingly ran through a most brilliant water-mirage lying directly before me. I could only see his head and part of his shoulders, for the rest of him was cut off by the air-layer; but the appearance was that of a wolf swimming rapidly across a lake of water. The illusion of the water was exact enough because it was produced by reflection, but there was no illusion about the upper part of the coyote. The rays of light from his head and shoulders came to me unrefracted and unreflected—came as light usually travels from object to eye.Colors and shadows in mirage.But refracted or reflected, every feature of the water-mirage is attractive. And sometimes its kaleidoscopic changes keep the fancy moving at a pretty pace. The appearance and disappearance of the objects and colors in the mirageare often quite wonderful. The reversed mountain peaks, with light and shade and color upon them, wave in and out of the imaginary lake, and are perhaps succeeded by undulations of horizon colors in grays and pinks, by sunset skies and scarlet clouds, or possibly by the white cap of a distant sierra that has been caught in the angle of reflection.Trembling air.But with all its natural look one is at loss to understand how it could ever be seriously accepted as a fact, save at the first blush. People dying for water and in delirium run toward it—at least the more than twice-told tales of travellers so report—but I never knew any healthy eye that did not grow suspicious of it after the first glance. It trembles and glows too much and soon reveals itself as something intangible, hardly of earth, little more than a shifting fantasy. You cannot see it clear-cut and well-defined, and the snap-shot of your camera does not catch it at all.Beauty of mirage.Yet its illusiveness adds to, rather than detracts from, its beauty. Rose-colored dreams are always delightful; and the mirage is only a dream. It has no more substantial fabric than the golden haze that lies in the canyons at sunset. It is only one of nature’s veilings whichshe puts on or off capriciously. But again its loveliness is not the less when its uncertain, fleeting character is revealed. It is one of the desert’s most charming features because of its strange light and its softly glowing opaline color. And there we have come back again to that beauty in landscape which lies not in the lines of mountain valley and plain, but in the almost formless masses of color and light.Footnotes[5]Century Dictionary.

Reality and appearance.

In our studies of landscape we are very frequently made the victims of either illusion or delusion. The eye or the mind deceives us, and sometimes the two may join forces to our complete confusion. We are not willing to admit different reports of an appearance. The Anglo-Saxon in us insists that there can be only one truth, and everything else must be error. It is known, for instance, that Castle Dome, which looks down on the Colorado River from Western Arizona, is a turret of granite—gray, red, brown, rock-colored, whatever color you please. With that antecedent knowledge in mind how difficult it is for us to believe the report of our eyes which says that at sunset the dome is amethystine, golden, crimson, or perhaps lively purple. The reality is one thing, the appearance quite another thing; but why are not both of them truthful?

Preconceived impressions.

And how very shy people are about acceptinga pink air, a blue shadow, or a field of yellow grass—sunlit lemon-yellow grass! They have been brought up from youth to believe that air is colorless, that shadows are brown or gray or sooty black, and that grass is green—bottle-green. The preconceived impression of the mind refuses to make room for the actual impression of the eyes, and in consequence we are misled and deluded.

Deception by sunlight.

But do the eyes themselves always report the truth? Yes; the truth of appearances, but as regards the reality they may deceive you quite as completely as the mind deceives you about the apparent. And for the deception of the eyes there is no wizard’s cell or magician’s cabinet so admirably fitted for jugglery as this bare desert under sunlight. Its combination of light and air seem like reflecting mirrors that forever throw the misshapen image in unexpected places, in unexpected lights and colors.

Distorted forms and colors.Changed appearance of mountains.

Distorted forms and colors.

Changed appearance of mountains.

What, for instance, could be more perplexing than the odd distortions in the forms and colors of the desert mountains! A range of these mountains may often look abnormally grand, even majestic in the early morning as they stand against the eastern sky. The outlines of the ridges and peaks may be clear cut, the lightand shade of the canyons and barrancas well marked, the cool morning colors of the face-walls and foot-hills distinctly placed and holding their proper value in the scene. But by noon the whole range has apparently lost its lines and shrunken in size. Under the beating rays of the sun and surrounded by wavering heated atmosphere its shadow masses have been grayed down, neutralized, perhaps totally obliterated; and the long mountain surface appears as flat as a garden wall, as smooth as a row of sand-dunes. There is no indication of barranca or canyon. The air has a blue-steel glow that muffles light and completely wrecks color. Seen through it the escarpments show only dull blue and gray. All the reds, yellows, and pinks of the rocks are gone; the surfaces wear a burnt-out aspect as though fire had eaten into them and left behind only a comb of volcanic ash.

Changes in line, light, and color.

At evening, however, the range seems to return to its majesty and magnitude. The peaks reach up, the bases broaden, the walls break into gashes, the ridges harden into profiles. The sun is westering, and the light falling more obliquely seems to bring out the shadows in the canyons and barrancas. Last of all thecolors come slowly back to their normal condition, as the flush of life to one recovering from a trance. One by one they begin to glow on chasm, wall, and needled summit. The air, too, changes from steel-blue to yellow, from yellow to pink, from pink to lilac, until at last with the sun on the rim of the earth, the mountains, the air, the clouds, and the sky are all glowing with the tints of ruby, topaz, rose-diamond—hues of splendor, of grandeur, of glory.

Suppose, if you please, a similar range of mountains thirty miles away on the desert. Even at long distance it shows an imposing bulk against the sky, and you think if you were close to it, wall and peak would loom colossal. How surprised you are then as you ride toward it, hour after hour, to find that it does not seem to grow in size. When you reach the foot-hills the high mountains seem little larger than when seen at a distance. You are further surprised that what appeared like a flat-faced range with its bases touching an imaginary curb-stone for miles, is in reality a group-range with retiring mountains on either side that lead off on acute angles. The group is round, and has as much breadth as length. And still greater is your surprise when you discover that the green topof the gray-based mountain, which has been puzzling you for so many hours, does not belong to the gray base at all. It is a pine-clad top resting upon another and more massive base far back in the group. It is the highest and most central peak of the range.

False perspective.Abnormal foreshortening.Contradictions and denials.

False perspective.

Abnormal foreshortening.

Contradictions and denials.

Such illusions are common, easily explained; and yet, after all, not so easily understood. They are caused by false perspective, which in turn is caused by light and air. On the desert, perspective is always erratic. Bodies fail to detach themselves one from another, foreshortening is abnormal, the planes of landscape are flattened out of shape or telescoped, objects are huddled together or superimposed one upon another. The disturbance in aërial perspective is just as bad. Colors, lights, and shadows fall into contradictions and denials, they shirk and bear false witness, and confuse the judgment of the most experienced.

Deceptive distances.

No wonder amid this distortion of the natural, this wreck of perspective, that distance is such a proverbially unknown quantity. It is the one thing the desert dweller speaks about with caution. It may be thirty or fifty miles to that picacho—he is afraid to hazard a guess. If you should go up to the top of your mountain rangeand look at the valley beyond it, the distance across might seem very slight. You can easily see to where another mountain range begins and trails away into the distance. Perhaps you fancy a few hours’ ride will take you over that valley-plain to where the distant foot-hills are lying soft and warm at the bases of the mountains. You may be right and then again you may be wrong. You may spend two days getting to those foot-hills.

Dangers of the desert.Immensity of valley-plains.

Dangers of the desert.

Immensity of valley-plains.

This deception of distance is not infrequently accompanied by fatal consequences. The inexperienced traveller thinks the distance short, he can easily get over the ground in a few hours. But how the long leagues drag out, spin out, reach out! The day is gone and he is not there, the slight supply of water is gone and he is not there, his horse is gone and he himself is going, but he is not there. The story and its ending are familiar to those who live near the desert, for every year some mining or exploring party is lost. If there are any survivors they usually make the one report: “The distance seemed so short.” But there are no short distances on the desert. Every valley-plain is an immense wilderness of space.

Shadow illusions.Color-patches on mountains.

Shadow illusions.

Color-patches on mountains.

There is another illusion—a harmless one—thathas not to do with perspective but with shadow and local color. The appearance is that of shadows cast down along the mountain’s side by the ridges or hogbacks. Any little patch of shadow is welcome on the desert, particularly upon the mountains which are always so strongly flooded with light. But this is only a counterfeit presentment. The ridges have no vegetation upon them to hold in place the soil and rocks and these are continually breaking away into land-slips. The slips or slides expose to view streaks of local color such as may be seen in veins of iron and copper, in beds of lignite or layers of slate. It is these streaks and patches of dark color that have broken away and slipped down the mountain side under the ridges that give the appearance of shadows. They have the true value in light, and are fair to look upon even though they are deception. The weather-beaten rocks of a talus under a peak may create a similar illusion, but the shadow effect loses a velvety quality which it has when seen under the ridges.

Illusion of lava-beds.Appearance of cloud-shadow.

Illusion of lava-beds.

Appearance of cloud-shadow.

The illusion of a cloud-shadow resting upon the foot-hills or in the valley, is frequently produced by the local color of lava-beds. Lava may be of almost any color, but when seen closeto view it is usually a reddish-black. At a distance, however, and as a mass, its beds have the exact value of a cloud-shadow. Any eye would be deceived by it. The great inundations of lava that have overrun the plains and oozed down the foot-hills and around the lomas (particularly on the Mojave) look the shadow to the very life. The beds are usually hedged about on all sides by banks of fine sand that seem to stand for sunlight surrounding the shadow, and thus the deception is materially augmented. Many times I have looked up at the sky to be sure there was no cloud there, so palpable is this lava shadow-illusion.

Mirage.Definition.

Mirage.

Definition.

But perhaps the most beautiful deception known to the desert is the one oftenest seen—mirage. Everyone is more or less familiar with it, for it appears in some form wherever the air is heated, thickened, or has strata of different densities. It shows on the water, on the grass plains, over ploughed fields or gravel roads, on roadbeds of railways; but the bare desert with its strong heat-radiation is primarily its home. The cause of its appearance—or at least one of its appearances—is familiar knowledge, but it may be well to state it in dictionary terms: “An optical illusion due toexcessive bending of light-rays in traversing adjacent layers of air of widely different densities, whereby distorted, displaced, or inverted images are produced.”[5]

Need of explanation.

This is no doubt the true explanation of that form of mirage in which people on Sahara see caravans in the sky trailing along, upside down, like flies upon the ceiling; or on the ocean see ships hanging in the air, masts and sails downward. But the explanation is very general and is itself in some need of explanation. Perhaps then I may be pardoned for trying to illustrate the theory of mirage in my own way.

Refraction of light-rays.Dense air-strata.

Refraction of light-rays.

Dense air-strata.

The rays of light that come from the sun to the earth appear to travel in a straight line, but they never do. As soon as they meet with and pass into the atmospheric envelope they are bent or deflected from their original direction and reach the earth by obtuse angles or in long descending curves like a spent rifle ball. This bending of the rays is called refraction, which must not be confounded with reflection—a something quite different. Now refraction is, of course, the greatest where the atmosphere is the densest. The thicker the air the more acute the bending of the light-ray. Hence the thick layersof air lying along or a few feet above the surface of the earth on a hot day are peculiarly well-fitted to distort the light-ray, and consequently well-fitted to produce the effect of mirage. These layers of air are of varying densities. Some are thicker than others; and in this respect the atmosphere bears a resemblance to an ordinary photographic or telescopic lens. Let us use the lens illustration for a moment and perhaps it will aid comprehension of the subject.

Illustration of camera lens.

You know that the lens, like the air, is of varying thicknesses or densities, and you know that in the ordinary camera the rays of light, passing through the upper part of the lens, are refracted or bent toward the perpendicular so that they reach the ground-glass “finder” at the bottom; and that the rays passing through the lower part of the lens go to the top of the “finder” The result is that you have on the “finder” or the negative something reversed—things upside down. That, so far as the reversed image goes, is precisely the case in mirage. The air-layers act as a lens and bend the light-rays so that when seen in our “finder”—the eye—the bottom of a tree, for example, goes to the top and the top goes to the bottom.

The bent light-ray.

But there is something more to mirage than this reversed image. The eyes do not see things “in their place,” but see them hanging in the air as in the case of ships and caravans. To explain this, in the absence of a diagram, we shall have to take up another illustration. Suppose a light-ray so violently bent by the heat lying above a sidewalk that it should come to us around a street corner, and thereby we should see a man coming up a side street that lies at right angles to us. He would appear to our eyes to be coming up, not the side street, but the street we are standing in. The man, to all appearances, would not be “in his place.” We should see him where he is not.

Ships at sea.Ships upside down.

Ships at sea.

Ships upside down.

Now suppose again instead of the light-rays bending to right or left (as in the street-corner illustration), we consider them as bending skyward or earthward. Suppose yourself at sea and that you are looking up into the sky above the horizon. You see there a ship “out of its place,” hanging in the air in an impossible manner—something which is equivalent, or at least analogous, to looking down the street and seeing the image of the man around the corner. You are looking straight into the sky, yet seeing a ship below the verge. The light-rayscoming from the ship on the water describe an obtuse angle or curve in reaching the eye. The rays from the bottom of the ship, lying in a dense part of the air-lens, are more acutely bent than those from the masts, and hence they go to the top of the photographic plate or your field of vision, whereas the rays from the ship’s masts, being in a thinner atmosphere, are less violently bent, and thus go to the bottom of your field of vision. The result is the ship high in air above the horizon-line and upside down.

Wherein the illusion.“Looming” of vessels, islands, and cities.

Wherein the illusion.

“Looming” of vessels, islands, and cities.

The illusion or deception consists in this: We usually see things in flat trajectory, so to speak. Light comes to us in comparatively straight rays. The mind, therefore, has formulated a law that we see only by straight rays. In the case of mirage the light comes to us on curved, bent, or angular rays. The eyes recognize this, but the mind refuses to believe it and hence is deceived. We think we see the ship in the air by the straight ray, but in reality we see the shipon the waterby the bent ray. It is thus that ships are often seen when far below the horizon-line, and that islands in the sea below the ocean’s rim, and so far away as a hundred miles, are seen looming in the air. “Looming” is the word that describes the excessiveapparent elevation of the object in the sky and is more striking on sea than land. Captains of vessels often tell strange tales of how high in the air, ships and towns and coasts are seen. The report has even come back from Alaska of a city seen in the sky that is supposed to be the city of Bristol. In tropical countries and over warm ocean-currents there are often very acute bendings of the light-rays. Why may it not be so in colder lands with colder currents?

Reversed image of mountains.Horses and cattle in mirage.

Reversed image of mountains.

Horses and cattle in mirage.

The form of mirage that gives us the reversed image is seen on the desert as well as on the sea; but not frequently—at least not in my experience. There is an illusion of mountains hanging peak downward from the sky, but one may wander on the deserts for months and never see it. The reality and the phantom both appear in the view—the phantom seeming to draw up and out of the original in a distorted, cloud-like shape. It is almost always misshapen, and as it rises high in air it seems to be detached from the original by currents of air drifted in between. More familiar sights are the appearances of trees, animals, houses, wagons, all hanging in the air in enlarged and elongated shapes and, of course, reversed. I have seen horses hitched to a wagon hanginghigh up in the air with the legs of the horses twenty feet long and the wagon as large as a cabin. The stilted antelope “forty feet high and upside down” is as seldom seen in the sky as upon the earth; but desert cattle in bunches of half a dozen will sometimes walk about on the aërial ceiling in a very astonishing way.

Illusion of rising buttes.

Yet these, too, are infrequent appearances. Nor is the illusion of buttes rising from the plain in front of you often seen. It happens only when there are buttes at one side or the other, and, I presume, this mirage is caused by the bending of the light-rays to the right or left. It presents certainly a very beautiful effect. The buttes rise up from the ground, first one and then another, until there is a range of them that holds the appearance of reality perhaps for hours, and then gradually fades out like a stereopticon picture—the bases going first and the tops gradually melting into the sky. When seen at sunset against a yellow sky the effect is magnificent. The buttes, even in illusion, take on a wonderful blue hue (the complementary color of yellow), and they seem to drift upon the sky as upon an open sea.

Other causes for mirage.Water-mirage.The lake appearance.How produced.

Other causes for mirage.

Water-mirage.

The lake appearance.

How produced.

The bending of the light-rays to either sideinstead of up or down, as following the perpendicular, may or may not be of frequent occurrence. I do not even know if the butte appearance is to be attributed to that. The opportunity to see it came to me but once, and I had not then the time to observe whether the buttes in the mirage had sides the reverse of the originals. Besides, it is certain that mirage is caused in other ways than by the bending of light-rays. The most common illusion of the desert is the water-mirage and that is caused by reflection, not refraction. Its usual appearance is that of a lake or sea of water with what looks at a distance to be small islands in it. There are those with somewhat more lively imagination than their fellows who can see cows drinking in the water, trees along the margin of the shore (palms usually), and occasionally a farm-house, a ship, or a whale. I have never seen any of these wonderful things, but the water and island part of the illusion is to be seen almost anywhere in the desert basins during hot weather. In the lower portions of the Colorado it sometimes spreads over thousands of acres, and appears not to move for hours at a stretch. At other times the wavering of the heat or the swaying of the air strata, or a change in thedensity of the air will give the appearance of waves or slight undulations on the water. In either case the illusion is quite perfect. Water lying in such a bed would reflect the exact color of the sky over it; and what the eyes really see in this desert picture is the reflection of the sky not from water but from strata of thick air.

Objects in the water.

This illusion of water is probably seen more perfectly in the great dry lake-beds of the desert where the ground is very flat and there is no vegetation, than elsewhere. In the old Coahuila Valley region of the Colorado the water comes up very close to you and the more you flatten the angle of reflection by flattening yourself upon the ground, the closer the water approaches. The objects in it which people imagine look like familiar things are certainly very near. And these objects—wild-fowl, bushes, tufts of swamp grass, islands, buttes—are frequently bewildering because some of them are right side up and some of them are not. Some are reversed in the air and some are quietly resting upon the ground.

Confused mirage.The swimming wolf.

Confused mirage.

The swimming wolf.

It happens at times that the whole picture is confused by the light-rays being both reflected and refracted, and in addition that the rays from certain objects come to us in a direct line.The ducks, reeds, and tufts of grass, for instance, are only clods of dirt or sand-banked bushes which are detached at the bottom by heavy drifts of air. We see their tops right side up by looking through the air-layer or some broken portion of it. But in the same scene there may be trees upside down, and mountains seen in reflection, drawn out to stupendous proportions. In the Salton Basin one hot day in September a startled coyote very obligingly ran through a most brilliant water-mirage lying directly before me. I could only see his head and part of his shoulders, for the rest of him was cut off by the air-layer; but the appearance was that of a wolf swimming rapidly across a lake of water. The illusion of the water was exact enough because it was produced by reflection, but there was no illusion about the upper part of the coyote. The rays of light from his head and shoulders came to me unrefracted and unreflected—came as light usually travels from object to eye.

Colors and shadows in mirage.

But refracted or reflected, every feature of the water-mirage is attractive. And sometimes its kaleidoscopic changes keep the fancy moving at a pretty pace. The appearance and disappearance of the objects and colors in the mirageare often quite wonderful. The reversed mountain peaks, with light and shade and color upon them, wave in and out of the imaginary lake, and are perhaps succeeded by undulations of horizon colors in grays and pinks, by sunset skies and scarlet clouds, or possibly by the white cap of a distant sierra that has been caught in the angle of reflection.

Trembling air.

But with all its natural look one is at loss to understand how it could ever be seriously accepted as a fact, save at the first blush. People dying for water and in delirium run toward it—at least the more than twice-told tales of travellers so report—but I never knew any healthy eye that did not grow suspicious of it after the first glance. It trembles and glows too much and soon reveals itself as something intangible, hardly of earth, little more than a shifting fantasy. You cannot see it clear-cut and well-defined, and the snap-shot of your camera does not catch it at all.

Beauty of mirage.

Yet its illusiveness adds to, rather than detracts from, its beauty. Rose-colored dreams are always delightful; and the mirage is only a dream. It has no more substantial fabric than the golden haze that lies in the canyons at sunset. It is only one of nature’s veilings whichshe puts on or off capriciously. But again its loveliness is not the less when its uncertain, fleeting character is revealed. It is one of the desert’s most charming features because of its strange light and its softly glowing opaline color. And there we have come back again to that beauty in landscape which lies not in the lines of mountain valley and plain, but in the almost formless masses of color and light.

Footnotes[5]Century Dictionary.

[5]Century Dictionary.

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