MIRRORS OF VARIABLE CURVATURE. 95 



Fig. 12, which is copied from an old one which 

 we have seen in use. 



Fig. 12. 



The method above described is equally appli- 

 cable to concave cylindrical mirrors, and to those 

 of a conical form ; and it may also be applied to 

 mirrors of variable curvature, which produce 

 different kinds of distortions from different parts 

 of their surfaces. 



By employing a mirror whose surface has a 

 variable curvature like ABC, Fig. 13, we obtain 

 an instrument for producing an endless variety 

 of caricatures, all of which are characterised by 

 their resemblance to the original. If a figure 

 M N is placed before such a mirror, it will of 

 course appear distorted and caricatured ; but even 

 if the figure takes different distances and posi- 

 tions, the variations which the image undergoes 

 are neither sufficiently numerous nor remarkable 

 to afford much amusement. But if the figure 

 MN is very near the mirror, so that new distor- 

 tions are produced by the different distances of 



