IV CONTENTS. 



LETTER III. 



Subject of spectral illusions Recent 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 3 affecting 

 the ear Spectre of a deceased friend sitting in an easy- 

 chair Spectre of a coach-and-four filled with skeletons 

 Accuracy 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 imagi- 

 nation are also pictures on the retina General views of 

 the subject Approximate explanation of spectral appa- 

 ritions ........ Page 37 



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 Cel- 

 lini Description and effects of the magic lantern Im- 

 provements 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 handwriting on 

 the wall His hollow cylindrical mirror for aerial images 

 Cylindrical mirror for re-forming distorted pictures 

 Mirrors of variable curvature for producing carica- 

 tures . 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 



