94 LETTERS ON NATURAL MAGIC. 



distorted, that the eye cannot trace in it the 

 resemblance to any regular figure, and the greatest 

 degree of wonder is of course excited, whether 

 the original image is concealed or exposed to 

 view. These distorted pictures may be drawn 

 by strict geometrical rules ; but I have shown in 

 Fig. 1 1 a simple and practical method of executing 

 them. Let M N be an accurate cylinder made of 

 tin-plate or of thick pasteboard. Out of the 

 farther side of it cut a small aperture abed ; and 

 out of the nearer side cut a larger one ABCD, 

 the size of the picture to be distorted. Having 

 perforated the outline of the picture with small 

 holes, place it on the opening ABCD, 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 ABCD 

 as the eye is afterwards to be placed before it, 

 and the light passing through the small holes will 

 represent on a horizontal 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 M N, then the distorted picture, when 

 laid horizontally at A'B'C'D', will be restored 

 to its original state when seen by reflexion 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 



