Miscellaneous optical illusions—Conversions of cameos into intaglios, or elevations into depressions, and the reverse—Explanation of this class of deceptions—Singular effects of illumination with light of one simple colour—Lamps for producing homogeneous yellow light—Methods of increasing the effects of this exhibition—Method of reading the inscription of coins in the dark—Art of deciphering the effaced inscription of coins—Explanation of these singular effects—Apparent motion of the eyes in portraits—Remarkable examples of this—Apparent motion of the features of a portrait, when the eyes are made to move—Remarkable experiment of breathing light and darkness
98
Natural phenomena marked with the marvellous—Spectre of the Brocken described—Analogous phenomena—Aërial spectres seen in Cumberland—Fata Morgana in the Straits of Messina—Objects below the horizon raised and magnified by refraction—Singular example seen at Hastings—Dover Castle seen through the hill on which it stands—Erect and inverted images of distant ships seen in the air—Similar phenomena seen in the Arctic regions—Enchanted coast—Mr. Scoresby recognizes his father’s ship by its aërial image—Images of cows seen in the air—Inverted images of horses seen in South America—Lateral images produced by refraction—Aërial spectres by reflexion—Explanation of the preceding phenomena
127
Illusions depending on the ear—Practised by the ancients—Speaking and singing heads of the ancients—Exhibition of the Invisible Girl described and explained—Illusions arising from the difficulty of determining the direction of sounds—Singular example of this illusion—Nature of ventriloquism—Exhibitions of some of the most celebrated ventriloquists—M. St. Gille—Louis Brabant—M. Alexandre—Capt. Lyon’s account of Esquimaux ventriloquists
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