PROPERTIES OP LENSES. 



Fig. 1. 



If the medium through which the light passes has 

 parallel faces, the emergent B'A' and incident rays 

 BA are parallel, (Fig. 1), if it has not, the ten- 

 dency of the ray is to bend away from the angle at 

 which the faces meet. 



Lenses are of six forms ; double convex 1, piano 

 convex 2, converging meniscus 3, double concave 4, 

 piano concave 5, diverging meniscus 6. 



Fig. 2. 



13 3 4 



miii 



