REFRACTION IN THE EYE 451 



objects) is 50.617 mm. The anterior focal dis- 

 tance is the same, for the lens is bounded by 

 media of equal density. 



CARDINAL POINTS OF THE EYE (SYSTEM C) 



Examine construction drawings of System A 

 (the cornea) and System B (the lens). System C 

 must be a combination of A and B. 



Note : 1. With System C as with System A 

 the first and last media have different refractive 

 powers. Therefore the principal points cannot 

 coincide with the nodal points. 2. The relation 

 between the nodal point k of System A and 

 the nodal points K\ and K z of System B is such 

 that the nodal points of System C will lie near 

 the posterior surface of the crystalline lens. 

 3. The principal point hi of System A lies on 

 the anterior surface of the cornea, and the prin- 

 cipal points Hi and H 2 of System B lie in the 

 lens. Hence those of System C must lie in the 

 aqueous humor. 4. In System C the collecting 

 power of System B is added to that of System 

 A. The focal distances in System C will there- 

 fore be less than those of A or B. 



Principal Surfaces. The principal surfaces are 

 found from the point s. If a perpendicular be 

 drawn at s the image of that perpendicular formed 



