KIECHEB'S MYSTEEIOUS HANDWRITING. 89 



necessary. This, however, though impracticable 

 with solid glass, may be easily obtained by means 

 of two large pieces of plate glass made into a 

 prismatic vessel and filled with water. Two of 

 the glasses of a carriage window would make a 

 prism capable of doubling the whole of the bust 

 of a living person placed as an object at AB, 

 Fig. 7, so that two perfectly similar phantasms 

 might be exhibited. In those cases where the 

 images before the lens L L are small, they may 

 be doubled and even tripled by interposing a 

 well-prepared plate of calcareous spar, that is, 

 crossed by a thin film. These images would 

 possess the singular character of being oppositely 

 coloured, and of changing their distances and 

 their colours, by slight variations in the positions 

 of the plate.* 



In order to render the images which are formed 

 by the glass and water prisms as perfect as pos- 

 sible, it would be easy to make them achromatic, 

 and the figures might be multiplied to any extent 

 by using several prisms, having their refracting 

 edges parallel, for the purpose of giving a simi- 

 larity of position to all the images. 



Among the instruments of natural magic which 

 were in use at the revival of science, there was 

 one invented by Kircher for exhibiting the mys- 

 terious hand- writing 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 



* See Edin. Encyclopaedia, Art. OPTICS, Vol. xv., p. 611. 



