“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 ship on the water by 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 excessive apparent 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 hanging high 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.