THE ACTION OF LIGHT 



coloured rays varying from violet to red. The 

 reason for this is that all the light rays composing 

 white light are not bent equally as they pass from 

 one medium to another. The violet rays are bent 

 the most, the indigo next, blue next, down to red, 

 which is least bent. Once more, considering the 

 double convex lens as made up of a number of 

 prisms, let us represent, by a diagram, the course 

 of parallel rays of white light through it. 



L 



AA^ represent the parallel rays of white light 

 falling on the lens, LL^. The blue rays are bent 

 more than the red, so the principal focus of the 

 former is at C and of the latter at D. The conse- 

 quence of this difference in bending of the various 

 coloured light rays would be most serious in micro- 

 scopic work were not means devised to overcome 

 it. Objects for instance at C in our diagram would 

 appear blue, at D they would appear red, whilst at 

 EE^ though no single colour would predominate 

 they would be illumined with many coloured rays, 

 though less strongly than at C or D. 



This chromatic aberration, as it is called, depends 

 amongst other things on the nature of the glass used 

 in lens construction. It has been found, however, 



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