FATA MORGANA. 649 



observed in cold climates, where the tiny ice particles are so abundant in the 

 air. These phenomena were recognized by the ancients, and halos round 

 the sun can be observed by means of darkened glasses. We annex, an 

 illustration of a mock sun and moon seen on the continent of Europe. 

 Readers of Mr. Whymper's " Scrambles in the Alps " will remember the 

 gorgeous, and to the guides mysterious, fog-bow or sun-bow seen as the 

 survivors of the first and most fatal ascent of the Matterhorn in 1865 were 

 tremblingly pursuing their descent over the upper rocks of that mountain. v 



The MIRAGE, or Fata Morgana, is a very curious but sufficiently 

 common phenomena, and in the Asiatic and African plains it is frequently 

 observed. When the weather is calm and the ground hot, the Egyptian 

 landscape appears like a lake, and the houses look like islands in the midst 

 of a widely-spreading expanse of water. This causes the mirage, which is 

 the result of evaporation, while the different temperatures of the air strata 

 cause an unequal reflection and refraction of light, which give rise to the 

 mirage. Travellers are frequently deceived, but the camels will not quicken 

 their usual pace until they scent water. 



The Fata Morgana and the inverted images of ships seen at sea are 

 not uncommon on European coasts. Between Sicily and Italy this effect is 

 seen in the Sea of Reggio with fine effect. Palaces, towers, fertile plains, 

 with cattle grazing on them, are seen, with many other terrestrial objects, 

 upon the sea the palaces of the Fairy Morgana. The inverted images of 

 ships are frequently perceived as shown in the illustration (fig. 729), and 

 many most extraordinary but perfectly authentic tales have been related con- 

 cerning the reflection and refraction of persons and objects in the sky and 

 on land, when no human beings nor any of the actual objects were within 

 the range of vision. 



It will be well to explain this phenomenon, and the diagrams will 

 materially assist us in so doing, for the appearances are certainly startling 

 when realized for the first time. The Spectre of the Brocken we see mimics 

 our movements, and we can understand it. But when apparently solid 

 buildings appear where no buildings have been erected, when we see as 

 has been perceived soldiers riding across a mountain by a path, or ledge, 

 perfectly inaccessible to human beings even on foot, we hesitate, and think 

 there is something uncanny in the sight. Let us now endeavour to explain 

 the mirage. 



Suppose that in the annexed diagram the space enclosed between the 

 letters A, B, C, D, be a glass vessel full of water. The ship is below the 

 horizon, the eye being situated at E the glass vessel of course representing 

 the atmosphere charged with moisture. The eye at E will perceive the top 

 of the mast of the ship, S, and we may imagine a line drawn from E to s. 

 Then put a (short focus) convex lens at a just above this (imaginary) line, 

 and a concave one, b, just over it. Through the former an inverted ship 

 will be seen, and an erect one through the latter at s' and s" respectively. 

 We now have the effect in the air just as reproduced in nature by the dif- 



