CATADIOPTRICAL PHANTASMAGORIA. 165 



the spectators would be quite overpowering. The lifeless 

 head might then be made to recover its vitality, and be 

 safely replaced upon the figure. If the head A of the 

 living object A B, Fig. 7, is covered with black cloth, the 

 head of a person or of an animal placed above A might be 

 set upon the shoulders of the figure A B by the refraction 

 of a prism. 



When the figure a 6, Fig. 8, is of very small dimensions, 

 as in the magic lantern, a small prism of glass would 

 answer the purpose required of it ; but in public exhibi- 

 tions, where the image a b must be of a considerable size, 

 if formed by a concave mirror, a very large prism would 

 be 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 A B, 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 possible, 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 similarity 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 

 * See Edin. Encyclopaedia, Art. OPTICS, vol. xv. p. 61 1. 



