170 



LETTERS ON NATURAL MAGIC. 



the picture with small holes, place it on the opening 

 A B C D so that its surface may be cylindrical. Let a 

 candle or a bright luminous object, the smaller the better, 

 be placed at S, as far behind the picture A B C D as the 

 eye is afterwards to be placed before it, and the light 

 passing through the small holes will represent on a hori- 

 zontal plane a distorted image of the picture A' B' C' D', 

 which when sketched in outline with a pencil, and shaded 

 or coloured, will be ready for use. If we now substitute 

 a polished cylindrical mirror of the same size in place of 



Fig. 12. 



M N, then the distorted picture when laid horizontally at 

 A ; B' C' D' will be restored to its original state when seen 

 by reflection at A B C D in the polished mirror. It 

 would be an improvement on this method to place at 

 A B C D a thin and flexible plate of transparent mica, 

 having drawn upon it with a sharp point or painted upon 

 it the figure required. The projected image of this 

 figure at A' B' C' D' may then be accurately copied. 



The effect of a cylindrical mirror is shown in Fig. 12, 

 which is copied from an old one which we have seen in 

 use. 



The method above described is equally applicable to 

 concave cylindrical mirrors, and to those of -a conical form, 



