PEOPERTIES OF LENSES. 



This ratio is called the refractive index. 



Refractive Index. 



Of Air 

 Diamond 

 Flint Glass 

 ,, Crown Glass 



1-000294 

 2-44 

 1-642 

 1-550 



A' 



If the medium through which the light passes has 

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

 rays are parallel, (Fig. 1), if it has not, the tendency 

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

 the faces meet. 



Lenses are of six forms; double convex 1, plano- 

 convex 2, converging meniscus 3, double concave 4, 

 plano-concave 5, diverging meniscus 6. 



