LIGHT. 



93 



an arc of a circle or any other curve, held in the 

 divergent beam of light, as shown in the figure, and 

 resting one edge upon a white wall or a piece of 

 white paper, will exhibit fine caustic curves, which 

 will change as the strirj is more or less bent. The 

 brighter the surface that reflects, the brighter will the 

 curves c c appear. Large rings, silvered and polished 

 on the inside, are sometimes used for this ; but a strip 

 of tin will answer well. 



CONVEX MIRRORS. 



The back of a concave mirror, such as already 

 mentioned, forms a very good convex mirror. Hold 

 that in the beam of light, in the same way as the con- 

 cave mirror was held, and note the result. Objects of 

 any size are usually much distorted when seen by 

 reflection in a convex mirror, as witness your own 

 countenance when looking into one. 



These distortions can be projected, though with 

 much loss of light, by strongly illuminating the object 

 o, and with an objective focus the reflection upon the 



Fig. 71. 



screen. In this way very humorous distortions of the 

 human countenance may be photographed by using 

 the camera at c. 



