CONTENTS. Tl 



FAQB 



LETTER III. 



Subject of spectral illusions Eecent and interesting case of 

 Mrs. A. Her first illusion affecting the ear Spectral 

 apparition of her husband Spectral apparition of a cat 

 Apparition of a near and living relation in grave-clothes 

 seen in a looking-glass Other illusions affecting the ear 

 Spectre of a deceased friend sitting in an easy-chair 

 Spectre of a coach and four filled with skeletons Ac- 

 curacy and value of the preceding cases State of health 

 under which they arose Spectral apparitions are pictures 

 on the retina The ideas of memory and imagination are 

 also pictures on the retina General views of the subject 

 Approximate explanation of spectral apparitions . . 120 



LETTER IV. 



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 Aerial 

 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 Philipstal and others Dr. 

 Young's arrangement of lenses, &c., for the phantas- 

 magoria Improvements suggested Catadioptrical phan- 

 tasmagoria for producing the pictures from living objects 

 Method of cutting off parts of the figures Kircher's 

 mysterious handwriting on the wall His hollow cylindrical 

 mirror for aerial images Cylindrical mirror for reforming 

 distorted pictures Mirrors of variable curvature for pro- 

 ducing caricatures 187 



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 in- 

 creasing the effect of this exhibition Method of reading 



