MIRAGE, mi-rfizIr' (Fr.. from mirer, to gaze). A phenomenon extremely common in certain lo calities. and due to existing in the at mosphere. As a result of a deviation of the ray.; of li ;Id caused by refraction and reflection. ob. jeets seen is Oh the eye appear in unusual positions and often molt iple or inverted. (Me cause of as oceurs in a desert. is a diminution of the density of the air ilea r t he sorfare t he ea rt 11, often produced by the radialitm of heat from the rt h. t he de•nse•r strat1nn being thus placed abort•, instead of, as is usually the ease. below the rarer. Nov, ran•. of light from a distant object. situated in the usermedium (i.e. a little above the earth'. level), coining in a direetion nearly par allel to the earth'. .nrfare, meet the rarer medium at a very obtuse• angle. and (see 1.4nur) instead of passing into it, they are reflected hack to the dense medium, the common surface of the two media as a mirror. The image produced by the reflected rays will appear in retied, and below the real object, just as an image reflected in water appears when observed from a distance. If the object is a cloud or por tion of sky, it will appear by the reflected rays as lying on the surface of the earth. :1:1(1 bearing a strong resemblance to a sheet of water: also, as the reflecting surface is irregular, and con stantly varies its position, owing to the constant communication of heat to the upper stratum. the
reflected image will be constantly varying, and will present the appearance of a water surface ruffled by the wind. This form of mirage is of common occurrence in the arid deserts of Lower Egypt. Persia. Turkestan, etc. In the case of mirage at sea the denser layers of air are next to the surface of the water, and the reflection takes place from the rarer atmosphere above. Conse quently we have the object appearing in the air suspended and inverted. Sometimes images of ob jeets are seen not above one another. but side by side. caused by the existence of bodies of air of different densities in proximity.
In particular states of the atmosphere reflec tion of a portion only of the rays takes place at the surface of the dense medium. and thus double images are formed, one by reflection, and the other by refraction—the first inverted and the second erect. The phenomena of mirage are fre quently much more strange and complicated, the images being often much distorted and magnified, and in some instances occurring at a considerable distance from the object. as in the ease of a tower or (thumb seen over the sea, or a vessel over dry land, etc. The particular farm of mirage known as looming is very frequently observed at sea, and consists in an excessive apparent elevation of the object. Consult Lrhr•bach der miselica !'hysiL• ( Brunswiek, 1896).