LETTER V.. Miscellaneous Optical Illusions--Conversions of Cameos Into

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