166 LETTERS ON NATURAL MAGIC. 



Kircher for exhibiting the mysterious handwriting on the 

 wall of an apartment from which the magician and his 

 apparatus were excluded. The annexed figure represents 

 this apparatus, as given by Schottus. The apartment in 

 which the spectators are placed is between L L and G H, 

 and there is an open window in the side next L L, 

 G H being the inside of the wall opposite to the window. 

 Upon the face of the plane speculum E F are written the 

 words to be introduced, and when a lens L L is placed at 

 such a distance from the speculum, and of such a focal 

 length that the letters and the place of their representa- 

 tion are in its conjugate foci, a distinct image of the 



Fig. 9. 



writing will be exhibited on the wall at G H. The letters 

 on the speculum are of course inverted, as seen at E F, 

 and when they are illuminated by the sun's rays S, 

 as shown in the figure, a distinct image, as Schottus 

 assures us, may be formed at the distance of 500 feet. In 

 this experiment the speculum is by no means necessary. 

 If the letters are cut out of an opaque card, and illumi- 

 nated by the light of the sky in the day, or by a lamp 

 during night, their delineation on the wall would be 

 equally distinct. In the daytime it would be necessary 

 to place the letters at one end of a tube or oblong box, 

 and the lens at the other end. As this deception is per- 

 formed when the spectators are unprepared for any such 



