90 LETTERS ON NATURAL MAGIC. 



01 ^ s 

 Fig. 9. 



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 

 representation are in its conjugate foci, a distinct 

 image of the writing will be exhibited on the wall 

 at GH. 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 illuminated 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 day-time 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 

 performed when the spectators are unprepared for 

 any such exhibition, the warning written in lumi- 

 nous letters on the wall, or any word associated 

 with the fate of the individual observer, could not 

 fail to produce a singular effect upon his mind. 



