PROPERTIES OF LENSES. 



11 



Fig. 8. 



through a medium (such as a lens or prism), Fig. 8, 

 whose sides are not parallel, it is divided into its 

 component colours, or dispersed. 



Fig. 9. 



Now since all the different rays into which a pencil 

 of white light can be divided, have different foci, 

 {e.g. the point where the red rays come to a focus 

 is more distant than that of the violet), the inter- 

 mediate colours forming other foci V 1 2 3 4 R Fig. 9 

 between them, are all unequally dispersed and the 

 resulting image will be coloured at its edges. 



There are several methods of remedying these 

 aberrations, some of them diminish Spherical and 

 Chromatic aberration at the same time. 



Spherical Aberration may be destroyed by giving 



