Science used as an instrument of imposture--Deceptions with plane and concave mirrors practised by the ancients--The magician’s mirror--Effects of concave mirrors--Aërial images--Images on smoke--Combination of mirrors for producing pictures from living objects--The mysterious dagger--Ancient miracles with concave mirrors--Modern necromancy with them, as seen by Cellini--Description and effects of the magic lantern--Improvements upon it--Phantasmagoric exhibitions of Philipstall and others--Dr. Young’s arrangement of lenses, &c., for the Phantasmagoria--Improvements suggested--Catadioptrical phantasmagoria for producing the pictures from living objects--Method of cutting off parts of the figures--Kircher’s mysterious hand-writing on the wall--His hollow cylindrical mirror for aërial images--Cylindrical mirror for re-forming distorted pictures--Mirrors of variable curvature for producing caricatures 56 LETTER V. 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 LETTER VI. 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 LETTER VII. 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 157 LETTER VIII.