Strobridge, In Miners' Mirage Land (Los Angeles, 1904); H.
3 Mirage and similar phenomena and the aurora are common.
North-west is the Store Vildmose, a swamp where the mirage is seen in summer.
MIRAGE (a French word, from mirer, to look at, se mirer, to be reflected), an optical illusion due to variations in the refractive index of the atmosphere.
A common type of mirage is the appearance of an isolated lake frequently seen in hot sandy deserts, as in the Sahara, Turkestan, &c. The explanation is as follows: The sand, being abnormally heated by the solar rays, causes the neighbouring air to expand, consequently its density, and therefore its refractive index, is diminished, and attains a minimum value in the lowest layers.