How does a mirage turn air into an apparent landscape?

A mirage can make a distant scene seem to shift rather than merely blur. Loudon recounts an occasion when the French coast appeared from Hastings, raised above the sea for nearly an hour before gradually sinking from view^[1]. In the Fata Morgana described in the account, a spectator facing a calm sea sees rapidly changing, multiplied images that resemble columns, arches, castles, palaces, trees, plains and animals. The account identifies them as objects in the Bay of Naples that would not ordinarily be visible from Sicily; it says they may also appear less distinctly in the air, or with rainbow-coloured fringes when the air is slightly hazy^[2][3].

Loudon’s 1848 explanation is that a suddenly heated surface warms the air immediately above it, making that lower layer less dense than the air above. Light passing between layers of different density bends, which the account describes as rays turning back and producing the altered view^[4]. To illustrate this, Loudon describes Brewster holding a heated iron over water, then replacing it with an iron bearing ice: the upper air cooled while the lower air remained warm, and the account says the lower layer produced mirage-like effects until the temperatures equalised^[5]. That is Loudon’s historical account, not a claim here that every detail of his explanation matches modern science.