KEFRACTION IN THE EYE 453 



FI A = 23.266 mm. 



F z A = 31.095 mm. 



f z A*= 2.179mm. 



The first principal point, HI C, is 

 23.266 x 2.179 ' _, 



31.095-2.179 



terior surface of the cornea. 



The second or posterior principal point of the 

 eye, H z 0, is the virtual image of s formed by the 

 lens. It also is found by formula (3 b). 



F^B = 50.617 mm. 



F Z B = 50.617 mm. 



ftB}= 3.547 mm. 



The second principal point, H z C, is 

 50.617 X 3.547 

 50617 3547 ~ ^* mm> Before tne posterior 



principal point of the lens ; this point lies 5.924 

 mm. behind the cornea ; hence H 2 C lies 5.924 

 3.814 = 2.11 mm. behind the anterior surface 

 of the cornea. The distance between the two 

 principal points is 2.11 1.75 = 0.36 mm. 



Nodal Points. The nodal points are virtual 

 images of the point o, which divides the distance 

 between the nodal points of System A and Sys- 



* The distance of the object s from the refracting surface, 

 in this case, the cornea. 



t The distance of the object s from the anterior principal 

 point of the crystalline lens. 



